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Dowload PDF - Image Communication on Short Waves

1. Mode Bandwidth Number ot Level of Transmission speed bps subcarriers MSC FEC QAM 4 QAM 16 QAM 64 A 2 3 kHz 53 normal 1480 2710 4170 low 1900 3470 5340 2 5 kHz 57 normal 1760 3220 4960 low 2260 4130 6360 B 2 3 kHz 45 normal 1070 1950 3000 low 1370 2500 3850 2 5 kHz 51 normal 1270 2320 3570 low 1630 2970 4580 E 2 3 KHz 29 normal 690 1270 1950 low 890 1620 2500 2 5 kHz 31 normal 820 1510 2320 low 1060 1930 2970 Table 10 2 The parameters of HamDRM modes and their transmission speed Parameter selection of HamDRM modes affects the transmission performance and hence the transmission speed which depends on the settings see table 10 2 The two corresponding stations should not communicate with each other in the same mode E g station X has a considerable local interference so station Y sends in a more resistant mode but Y hasn t this problem so X can easily transmit in a faster but less resistant mode If the transfer of some segments fails completely it is not lost at all because your QSO partner can send bad segment report BSR and you can resend bad segments again It s important to send BSR in same mode The repeated segments can be received third station too and if have not all segments received it can complete 119 10 DSSTV TRANSMISSION SYSTEMS whole data When band conditions are really bad and part of resend fails again it is possible to generate the new
2. Mode Transfer VIS Color Scan line ms Speed Resolution name time 16 bit sequence Sync Y R Y B Y Ipm MP115 115s 320x256 0x2923 YCrCb 9 0 223 0 223 0 223 0 133 037694 MP140 140s 320x256 0x2a23 YCrCb 9 0 270 0 270 0 270 0 110 091743 MP175 175s 320x256 0x2c23 YCrCb 9 0 340 0 340 0 340 0 87 591241 MR73 73s 320x256 0x4523 YCrCb 9 0 138 0 69 0 69 0 419 140761 MR90 90s 320x256 0x4623 YCrCb 9 0 171 0 85 5 85 5 340 618791 MR115 115s 320x256 0x4923 YCrCb 9 0 220 0 110 0 110 0 266 489007 MR140 140 s 320x256 0x4a23 YCrCb 9 0 269 0 134 5 134 5 218 858289 MR175 175s 320x256 0x4c23 YCrCb 9 0 337 0 168 5 168 5 175 361683 ML180 180s 640x496 0x8523 YCrCb 9 0 176 5 88 25 88 25 330 305533 ML240 240 s 640x496 0x8623 YCrCb 9 0 236 5 118 25 118 25 248 292986 ML280 280 s 640x496 0x8923 YCrCb 9 0 277 5 138 75 138 75 212 276667 ML320 320s 640x496 0x8a23 YCrCb 9 0 317 5 158 75 158 75 185 960019 Narrowband modes Mode Transfer Color Scan line ms Speed Resolution N VIS name time sequence Sync Y R Y B Y lpm MP73 N 738 320 x 256 0x02 YCrCb 9 0 140 0 140 0 140 0 210 526316 MP110 N 115s 320 x 256 0x04 YCrCb 9 0 212 0 212 0 212 0 139 860140 MP140 N 140s 320x256 0x05 YCrCb 9 0 270 0 270 0 270 0 110 091743 Sync R G B MC110 N 110s 320x256 0x14 R G B 8 0 143 0 143 0 143 0 137 142857 MC140 N 140s 320x256 0x15
3. Figure 7 10 The configuration of accurate timing with RMW re ception in MMSSTV A A a 106 For the f 11024 45 Hz the deviance in ppm is A 0 55 A L 106 7 108 ppm 50 ppm F 11025 00 PPP Pp 7 3 1 Transmit timing offset There is necessity to configure transmit timing TX offset after the precise config uration of reception sample rate when received SSTV images are not slanted It is important for your own transmission because inaccurate transmit timing causes image slant on reception side Some programs makes possible to monitor outgoing SSTV signals so with this feedback it is practicable to check the T X offset deviance between reception and transmission sample rate The feedback can be internal or external Eztenal feedback needs to connect Line Out and Line In with cable and it requires a sound card with full duplex mode enabled By this way you can set T X offset precisely on your own The internal feedback doing almost the same but no external cables is needed But some sound cards support only software feedback so you will find zero deviance but it is not real fact Then the TX offset setting must be done with external feedback or with opposite station help You need to disable any automatic corrections of received signals in this way 75 7 COMPUTER OPERATIONS Anyway you need to make dry run QSO before your first CQ This helps you to uncover possible problems with TX offs
4. 107 9 INTRODUCTION TO DIGITAL SLOW SCAN TV PNG 1 016 Bytes JPEG 1 quality 1 378 Bytes Figure 9 6 The detail of image with unproper compression provements There are used more sophisticate mathematical methods The DCT is not used but discrete wavelet transformation DWT Wavelet transformation is one of methods for frequency domain representation of signal and has some advan tages over DCT A functions with defined wave shape are used instead of sinuses and cosinuses Thanks to new transform method the compress ratio is better about 20 to 30 The images with sharp edges and color gradients have lower distortion Users of new format appreciate the most a better compression ratio and higher image quality when using the lossy compression DCT in JPEG format requires the division of the image into small 8 x 8 blocks while JPEG2000 uses the whole image The RGB color coding is used And in addition the user has the choice to mark area of interest These areas are part of the image where is required to set lower or higher compression ratio For use in DSSTV is advantageous fault tolerance of the data stream Only a small portion of the image displays poorly in the case of 108 INTRODUCTION TO DIGITAL SLOW SCAN TV 9 faulty transmission other sections carried well are not affected For older JPEG the image part following the fault data of stream used to be completely discarded 14 628 B 7 310B Ra
5. Parameters of the RS n k are defined as follows gt s number of bits in one informational symbol gt k number of s bit symbols in data block n number of bits in codeword RS n k is able to correct nok errors in k information symbols Often used code is RS 255 223 it uses 223 8 bit symbols for creation of 255 symbols of codeword There is 32 symbols dedicated for error correction RS 255 223 is able to repair up to 16 erroneous 8 bit symbols 9 3 Data compression The image with resolution 320x240 with a color depth of 16 million colors 256 takes 230 400 Bytes 320x240x3 without compression This file would be trans mitted fortyone minutes by RDFT with speed 92 Bytes per second This time is really scary in comparison with analog SSTV It is really necessary to reduce the file size and reduce the time required for transmission The data compression is widely used in such cases where the data capacity of communication channels or storage media and memory is limited The compression is the process where the physical data block size is reduces to a certain level Input data is compressed using the compression algorithm and 99 9 INTRODUCTION TO DIGITAL SLOW SCAN TV then stored on media or transmitted via communication channel The data are decompressed in its original form when a media is read or a signal received One of the important parameters of compression algorithms is lossy While the progr
6. Y and B Y Due to this the color modes are compatible with their B amp W variants So a 12s color mode can be displayed by 8s monitors etc From a total of 8 modes 4 are intended for color transmission Half of the color modes use YCrCb in a 4 2 0 format The scan line contains only one chrominance signal and colors are obtained from the average of two adjacent lines in the original image The other two modes use the 4 2 2 format and send all color information in one scan line The original Robot system uses asynchronous transfer To receive the image it is needed to detect the vertical sync VIS code And for proper reception of the image the sync pulse must be detected This process is a major disadvantage P LIS df 2300 ND HB 1900 U gt b U o aj U u e 500 1200 0 50 100 150 200 250 300 Time t ms Figure 4 2 Two scan lines of Robot 36 Color when color bars are sent The scan line is composed of the starting sync followed by a short 3 0ms gap of 1500 Hz and then the image part with luminance and chrominance The chrominance 33 4 FORMATS OF SLOW SCAN TV TRANSMISSION differential signals begin with additional sync pulses The 1500Hz sync is before R Y and the second 2300Hz is before B Y Due to the additional sync with a different sync frequency it is possible to re synchron
7. can be clearly reconstructed from a sequence of evenly spaced samples with a sampling frequency f greater than double f f gt Py M You can see the importance of Shannon s theorem in the example below The signal in figure 7 2a expresses the dependency between time t and amplitude A Using Fourier s analysis we can find see chapter 3 1 1 that the signal contains two harmonic components showed in 7 2b A A a Surveyed signal b Spectral components Figure 7 2 Example of signal By using Fourier s transformation the signal can also be expressed as a dependency between amplitude A and frequency f signal spectrum Both frequency compo nents are evident f and fy fmax in the signal in fig 7 3 For explicit signal reconstruction the condition f gt 2f maz must be satisfied see fig 7 4 If a sampling frequency is lower then 2 then the higher frequency components are lost This error is called aliasing For the sampling of common narrow band signals like SSTV RTTY PSK31 or WEFAX which are transferred via SSB channel with a bandwidth of about 2500 3 000 Hz a sample rate of 11 025 Hz is enough 7 2 2 Analog to digital conversion The next way of an analog signal continues to the analog to digital A D converter The current value of signal converted into digital data in this device Some A D converters works with a resolution 8 or 16 bits according to type or settings of a sound card The resolution of A D conv
8. gt Kilometric waves 30 kHz 300 kHz Centre frequency fo gt Frequency corresponding to black fy 150 Hz gt Frequency corresponding to white f 150 Hz 146 12 List of professional stations There is list of HF professional stations Be sure to tune in USB mode for 1 9 kHz lower Time values are given in UTC Coordinated Universal Time 12 1 Europe 12 1 1 Athens Greece Ident Frequency lpm IOC Power Note SVJ4 4 481 0 kHz 120 576 8kW 08 45 10 44 SVJ4 8 105 0 kHz 120 576 8kW 08 45 10 44 Broadcast time 08 45 10 44 12 1 2 Hamburg Pinnenberg Germany Ident Frequency lpm IOC Power Note DDH3 3 855 0 kHz 120 576 10 kW DDK3 7 880 0 kHz 120 576 20 kW DDK6 13 882 5 kHz 120 576 20 kW Broadcast time 04 30 11 45 15 20 22 00 12 1 3 Roma Italy Ident Frequency lpm IOC Power Note IMB51 4 777 5 kHz 120 576 5 kW IMB55 8 146 6 kHz 120 576 5 kW IMB56 13 597 4 kHz 120 576 5 kW 147 12 LIST OF PROFESSIONAL STATIONS Broadcast time continuous 12 1 4 Moscow Russia Ident Frequency lpm IOC Power Note 3 830 0 kHz 90 120 576 288 5 008 0 kHz 90 120 576 288 6 987 0 kHz 90 120 576 288 7 695 0 kHz 90 120 576 288 RCC76 10 980 0 kHz 90 120 576 288 RDD78 11 617 0 kHz 90 120 576 288 RCC76 10 980 0 kHz 90 120 576 288 Broadcast time continuous 12 1 5 Murmansk Russia Ident Frequency lpm IOC Power Note RBW41 5 336 0 kHz 90 120 576 RBW41 6 445 5 kHz 90 120 576 main f
9. 2300 y Caa ND E 1900 a o ES 1500 E 1200 3400 3600 3800 4000 4200 4400 Time t ms Figure 4 7 The digital synchronization header of AVT 90 mode VIS 68 normal variant The first three bit of each 8bit word identifies the mode gt 010 AVT 24 gt 011 AVT 94 AVT 188 AVT 125 BW gt 101 AVT 90 The last five bits are used as a count down before image transmission Actually these five bits are important for an accurate set of image initiation and synchro nization They vary between all 32 binary combinations during transmission At least one binary code must be properly detected At the beginning all bits are in 0 states with 1 in inverted parts When the countdown starts all five bit sequences run e g for AVT 24 010 00000 101 11111 010 00001 101 11110 010 00010 101 11101 010 11101 101 00010 010 11110 101 00001 010 11111 101 00000 41 4 FORMATS OF SLOW SCAN TV TRANSMISSION When the count down gets to zero the image scan lines are sent AVT recep tion depends on the first eight seconds of synchronization for some implementations without the ability to synchronize later Although the AVT modes are quite reli able noise could cause a loss of the whole image Sometimes it is not possible to receive a digital header due to interference even if the interference later disappears However the origi
10. C Alpha weighting Help Reset Cancel Ie Figure 13 7 Convolution matrix parameters in GIMP 13 3 2 Noise reduction Thanks to noise reduction it is possible to improve partially received SSTV or WE FAX images by smoothing It can be done several ways Since SSTV transmission takes a relatively long time the noise levels are often uneven affected by random interference and transmission conditions so you can by tool Selection mark affected areas where apply the filter 13 3 2 1 Spatial average filtering The simplest way to reduce noise is average filter with convolution kernel H4 ij ii H 5 1 1 1 111 The next useful matrices for averaging are Hy and Hg they aren t using neighbor pixel with same weight but near pixels have greater coefficients then farther The values of the coefficients are based on binomial series 168 COMPUTER IMAGE PROCESSING 13 14 6 4 1 T 2 2 1 4 16 24 16 4 x 3 2 Ha gt 5 24 36 24 6 3 4 16 24 16 4 14 6 4 1 The disadvantage of averaging filters is that smoothing distorts sharp color gradients and due to it thin lines and other details are distorted Received image Averaging H Binom filter 3 x 3H Binom filter 5 x 5H Figure 13 8 Next filters for noise reduction in GIMP are in menu Filters gt Blur E g Gaussian blur is useful for SSTV noise reduction the user can set a radius of a blur For image preparation can be used Selective
11. E g for QAM 16 levels are 3 1 1 3 The signal which can be presented like S t A cos 2r ft g has 16 combinations of amplitudes A and phases gy The block diagram of QAM modulator see in fig 10 10 Now we describe how QAM 16 modulates data sequence N 40 13 5 2 10 7 6 5 1 15 The result is fig 10 12 The information words with 4bit length are divided on two parts in mapping circuit and first 2bit combination is coded in pulse amplitude modulation PAM into one of four levels The way how to code input bit quaternion io i1 qo q is defined by constellation diagram fig 10 11 E g for input 0 it is ty y 00 dudi 00 and this corresponds to I 3 Q 3 the next value 13 in binary 1101 corresponds 294 11 output I 3 and for q9q 01 output Q 1 etc The results of PAM are pulses with given amplitudes and they are filtered with low pass filter for the bandwidth reduction and for in phase path J and similarly for quadrature path Q The J and Q are input signals for modulators with carrier 122 DSSTV TRANSMISSION SYSTEMS 10 frequency f This way there is a phase of 90 between them Output signal is made by joining of both paths together S t I cos 2n ft Qg sin 27 ft o D cca 4 1111 0111 1011 0011 lo 1 0 1 0 K d 1 0 0 Figure 10 11 The constellation diagram for QAM 16 with bit order 49 44 qo q used in DRM 10 2 3 Orthogonal frequency division multip
12. modulator RGB multiplexer AID converter ET NTSC PAL video to RGB input converter RF output for TV receiver system clock display controller SSTV FM signal SSTV input gt gt zero detector E COMPUTER FM modulator output interface for computer and fronit pone printer contro Figure 6 5 Block scheme of stand alone SSTV FSTV converter Robot 1200C was modified with optional EPROMs and a timing circuit so it can be used for operations in various SSTV modes Its production ended in 1992 but during the nineties there were clones available on the market FH 21P in Germany SUPERSCAN 2001 in the United Kingdom LM 9000C and Ribbit 1200C These machines can still be used for SSTV operations and many old school operators own them They are also sometimes available in Ebay auctions 6 5 SUPERSCAN 2001 The production of SUPERSCAN started shortly after the end of Robot 1200C pro duction Its designer Jad Bashour had worked with Martin Emmerson SUPER SCAN is actually a much improved 1200C and includes improved modifications to the original 1200C The price of this unit was about 750 and with additional modules the price could exceed 1000 62 SSTV EQUIPMENT 6 Figure 6 6 The front panel of SUPERSCAN 2001 Main features of SUPERSCAN 2001 gt Total compatibility with all classic SSTV systems gt S
13. An example of OFDM spectrum is in fig 10 13 as spectrum of each subcarrier is considered the spectrum of rectangular signal which is expressed by sin a a function The subcarriers has exact distances so maximal level of spectrum of each subcar rier is null in maximal levels of other subcarriers so they are mutually orthogonal 10 2 3 1 OFDM transfer The modulator block diagram is in fig 10 14 Input data stream comes to ser ial parallel converter and it is cyclically distributed to a larger number of parallel 124 DSSTV TRANSMISSION SYSTEMS 10 Amplitude A Frequency f Figure 10 13 The frequency spectrum of orthogonal carrier waves components The parallel component transmitted simultaneously creates a com plete OFDM symbol Components are also modulated to the orthogonal system of N subcarriers the frequencies are distributed to ensure their orthogonality Subcar rier waves in our case use modulation QAM 4 QAM 16 or QAM 64 but for some other applications there are used multiphase BPSK or QPSK A signal processor provides modulation of huge number of subcarriers in our case it is software which implements algorithms for inverse discrete Fourier transform DFT Because DFT algorithm has big computing complexity there is used its faster variant FFT Fast Fourier Transform The inverse FFT FFT 1 transform input data from frequency domain to time domain The process on a receiver side vice versa us
14. Scottie S1 60 0x3C 0111100 Scottie S2 56 0x38 0111000 Scottie DX 76 Ox4C 1001100 Wraase SC 2 180 55 0x37 0110111 Table 3 2 The VIS codes of popular modes 2300 p 1900 1500 Frequency f Hz 1300 1200 1100 0 100 200 300 400 500 600 700 800 900 Time t ms Figure 3 12 The vertical synchronization of Martin M1 the VIS code value is 44 27 Formats of slow scan TV transmission 4 1 Black and white SSTV systems The earlier modes of SSTV transmission were displayed on long persistent monitors with radar CRT The duration of transmission for each image frame took 7 2 to 8 seconds and when the last line was received the first line was still visible It was possible to see the whole picture in a darkened room Both 7 28 and 8s modes were used in the same period The 7 2s frame speed mode was used in Europe while the 8s were used in America The synchronization of signals is derived from the electrical mains 50 or 60 Hz If an image was syn chronized at 60 Hz and received on 50 Hz equipment it was still readable but the image was a little distorted For long distance QSOs it was possible to change the oscillator to achieve European or American synchronization The disadvantages of 8s SSTV are low image resolution and a loss of synchroniza tion due to signal interference The loss of synchronization coul
15. Wraase DL2RZ Each of them introduced an SSTV converter which used each company s own transmission system The systems are different in the usage of colour coding scan line formats and synchronization methods Their converters provide several modes Mode denotes a format of image transmission its resolution and transfer speed As often happens the professional device did not fully satisfy ham radio users So new systems with more modes were implemented into the converter firmware And they were also re implemented into other devices to ensure compatibility Sometimes a new genuine system was designed to overcome imperfections found in the classic predecessors The number of those systems has grown unbelievably Recently they were new systems created for better utilization of modern computer potentials Modern per sonal computers with the necessary equipment are full successors of SSTV con verters The advantage of computers is especially bigger memory and better image resolution 12 MODERN SSTV FEATURES 3 If we were to count the number of all SSTV modes we would find approximately 70 So it is possible to transfer SSTV images via seventy different modes which are mutually different in transmission time resolution colour coding etc The vast majority of them are absolutely unique and incompatible You might be a little scared by the previous paragraphs but let me reassure you that only a few modes are actually used Europ
16. 20 45 17 151 2 NMC Pt Reyes California USA 120 576 17 430 0 9VF 252 Kyodo News Agency Singapore 60 576 07 40 10 10 14 15 18 15 18 060 00 VMW Wiluna Australia 120 576 21 00 11 00 18 236 09 BAF33 Beijing China 120 576 18 261 0 GYA Northwood Persian Gulf Base 120 576 08 00 18 00 18 560 0 BMF Taipei China 120 576 18 940 0 BDG Shanghai China 120 576 20 469 0 VMC Charleville Australia 120 576 19 00 09 00 22 527 0 NMC Pr Reyes California USA 120 576 18 40 23 56 22 542 0 JJC Kyodo News Agency Japan 60 576 meteo maps 120 Ipm 160 15 Computer image processing This chapter focuses on a preparation of our broadcast contents image and photo editing before the transmission There are available many programs for image editing from complex editors for bitmap images to simple viewers with few editing functions Some SSTV programs have also image editing functions The selection of suitable program depends on a user and his needs and although a control of programs can be slightly different the procedures described later are so general that it would not be a problem to achieve results using your favorite editor The appropriate editor is generally any program for editing of raster bitmap images such as GIMP Paint Shop Pro Adobe Photoshop Pixel32 Less suitable are vector image editors such as Corel Draw Inkscape etc There are described some basic principles and functi
17. 7 420 0 kHz 120 576 BDF 11 420 0 kHz 120 576 BDG 18 940 0 kHz 120 576 Broadcast time 00 10 01 30 18 10 20 30 12 3 4 New Delhi India Ident Frequency lpm IOC Power Note ATP57 7 404 9 kHz 120 576 10 kW 14 30 02 30 ATP65 14 842 0 kHz 120 576 10 kW 02 30 14 30 Broadcast time continuous 12 3 5 Tokyo Japan Ident Frequency lpm IOC Power Note JMH 3 622 5 kHz 120 576 5 kW JMH2 7 305 0 kHz 120 576 5 kW JMH4 13 597 0 kHz 120 576 5 kW Broadcast time continuous 12 3 6 Pevek Chukotka peninsula Ident Frequency lpm IOC Power Note 148 0 kHz 90 576 Broadcast time 05 30 07 30 11 30 13 30 14 30 16 30 150 LIST OF PROFESSIONAL STATIONS 12 3 7 Taipei China Ident BMF BMF BMF BMF BMF Frequency lpm IOC Power Note 4 616 0 kHz 5 250 0 kHz 8 140 0 kHz 13 900 0 kHz 18 560 0 kHz 120 120 120 120 120 516 516 516 516 516 10 kW 10 kW 10 kW 10 kW 10 kW Broadcast time 00 40 10 10 13 10 22 10 12 3 8 Seoul Republic of Korea Ident HLL1 HLL2 HLL3 HLL4 HLL5 Frequency lpm IOC Power Note 3 585 0 kHz 5 857 5 kHz 7 433 5 kHz 9 165 0 kHz 13 570 0 kHz 120 120 120 120 120 576 576 576 576 576 3 kW 3 kW 3 kW 3 kW 3 kW Broadcast time 00 00 10 40 12 00 22 40 12 3 9 Bangkok Thailand Ident Frequency lpm IOC Power Note HSW64 7 396 8 kHz 120 576 3kW Broadcast time 00 50 06 00 07 20 10 20 13 00 17 00 23 00 12 3 10 Kyodo News Agency Japan
18. A Multi operators 85 8 HAM RADIO IMAGE OPERATIONS all bands B One operator all bands legal in Russia C One operator all bands D One operator one band E listener A CQ image should contains CQ RUSTEST Transmit RSV and the number of QSOs beginning with 001 Russian stations trans mit RSV zone and number of QSOs Scoring 6 points for each QSO plus 2 points for QSO with MsstvS member additional points for QSO with station from MsstvS scoring list Final score total sum of points plus additional points Send log sep arately for each band must include band date time in UTC call sign messages sent and received Stations with multiple operators must deliver list of names and signatures for all operators The log send to 24th April Organizer Russian SSTV Contest Manager Krenkel of CRC Russia P O Box 88 Moscow Russia 8 4 3 NVCG SSTV Contest The contest is organize Nishi Nippon Visual Communication Group and takes up 9 days in July Score is 2 points for two way SSTV QSO with NVCG member they used M letter in report e g 595M and 1 point for another QSO Only one QSO with same station is counted regardless of band The multiplier is the total number of different prefixes Send log to Susumu Tokuyasu JA6GN 3 1 6 Jyousei Sawaraku Fukuoka 814 0003 Japan or email sstv contest nvcgQwak bbiq jp 8 4 4 Danish SSTV Contest The contest is organized by Danish SSTV Group Takes place first weekend in May f
19. BSR so the amount of transfered data will be lower in next resent The DRM transfer consist of three channels MSC SDC and FAC Each channel is dedicated for transmission of certain data or service information and also for each is used different coding and modulation scheme MSC Main Service Channel contains data for all services of DRM multiplex The multiplex can contain one to four services and each can transfer data or service information FAC Fast Access Channel is support channel It uses QAM 4 and broadcast callsign DRM mode identification band spectrum occu pancy interleaving mode of MSC and SDC modulation FAC channel with service information transfer packet with 40 bit size VVVVVVY V V D D D 2 bit FRAME ID identifies a frame in a superframe value 0 1 2 1 bit Spectrum Occupancy 2 3 2 5 kHz 1 bit Interleaver Depth 400 ms 2s 1 bit MSC Mode QAM 16 QAM 64 1 bit Protection Level amount of FEC used 1 bit Audio Data if audio is used then follows gt 2 bit audio codec LPC unused SPEEX gt 1 bit text flag if data is used then follows gt 2 bity Packet ID gt 1 bit extended MSC mode QAM 4 21 bits Label consisting of 3 x 7 bit ASCII characters 9 char acters in superframe 1 bit dummy 8 bit CRC used polynomial G x x8 z z z 1 SDC Service Description Channel contains information of MSC decod ing scheme and broa
20. Ma rine Worldwide Radiofacsimile Broadcast Schedules which is published by the Na tional Oceanic and Atmospheric Administration s NOAA and it s freely available to download Radiofacsimile Worldwide Marine Broadcast Schedules http www nws noaa gov om marine rfax pdf Another excellent source of information for those who are interested in receiving of meteorological data is the website of the World Meteorological Organizations W M O Besides general information about meteorology there are lists of frequencies and schedules not only for the fax but also for other professional stations which use for distribution radio teletype RT TY NAVTEX and other types of digital modes World Meteorological Organization http www wmo ch 11 4 Satellite imagery retransmission Following list is compiled from It s the list of stations retransmitting meteo satellites imagery All listed stations transmit in 1201pm and IOC 576 138 FACSIMILE RADIOFAX 11 UTC 00 34 00 48 01 01 01 10 01 20 01 43 01 54 02 00 03 51 05 06 06 35 06 49 07 10 07 20 07 37 08 00 09 06 09 08 09 43 09 51 10 22 11 17 11 30 12 32 12 48 13 10 13 20 14 00 14 03 14 14 15 03 16 45 Station Hawai USA Hawai USA Halifax Canada Tokyo Japan Taipei China California USA California USA Lousiana USA Massachusetts USA Alaska USA Hawai USA Hawai USA Tokyo Japan Taipei China California USA Lousiana USA Hawai USA Califo
21. Picture Transmission signal see section 11 2 1 44 FORMATS OF SLOW SCAN TV TRANSMISSION 4 4 3 2 Pasokon TV These synchronous modes were released with Pasokon T V interface from John Langer WB5OSZ These modes retain essential SSTV parameters They also used color coding to transmit the individual color components in the order of red green blue with the format 1 1 1 There are three modes in the Pasokon system They have different transmission times 3 5 or 7 minutes so the image quality differs Each mode has a default timing for scan lines gt Pasokon P3 4800 Hz gt Pasokon P5 3200 Hz gt Pasokon P7 2400 Hz The scan line starts with a sync of 20 time units then there is a 5 unit black gap followed by the red component It has 640 units so there is one unit for each pixel There are 5 unit black gaps between color components and at the end of the scan line before the sync of the next line These gaps should help improve the detection of syncs Pasokon P7 has the best image quality and longest tramsmission time which takes nearly seven minutes If we split such an image into four equal parts the image quality of one of them would correspond to that produced by the Martin M1 or Scottie S1 modes The upper 16 lines are used for gray scale and the remaining 480 for your own image There are also two other modes with 4804 16 lines The P5 has a transfer time of almost 5 minutes with lower image qualit
22. SSTV use even parity This means that the number of logical ones must be even in the whole 8bit code If the number of ones in 7 bits is odd then the parity bit is set to one If the number is even the parity bit is zero Since the information part of code has 7 bits it takes 128 values Each bit is 30ms long so the modulation speed is 33 3 bauds The frequency 1300 Hz means the state of logical zero and 1100 Hz logical one The first half of code least significant bits LSB specifies the type of mode BW colour resolution The second half most significant bits MSB contains information about the system Robot Martin AVT The last bit is reserved for parity error checking The meaning of bits table 3 1 is valid for a system based on Robot Research standard As the number of new modes have expanded the bit combination has no additional meaning The comprehensive table of all VIS code is on page 53 There is a vertical synchronization in fig 3 12 with a value of 10101100 44 decimal The parity bit is 1 and first three bits 010 distinguish the Martin system The vertical and horizontal resolution can be determined from the value of the second nibble 1 256 lines and 1 320 columns the last two bits with value 00 mean colour transmission 3 6 3 Additional synchronization data Some SSTV software append a signal with additional data to the synchronization e g call sign identification which can then be decoded and used as a
23. Their effects are not negligible The intensity of this effect depends also on the frequency of signal Generally it is always possible to identify a range of frequencies that a particular transmission path can transfer well and outside this frequency range the transmission is too poor The signal bandwidth does not depend only on the frequency range used for modulation in our case 1 500 Hz to 2 300 Hz but also on the signal spectrum Fourier analysis is used to determine the spectrum bandwidth The analysis can express any waveform in the form of the sum of a large number of sine waves harmonic components 13 3 MODERN SSTV FEATURES Limited bandwidth has the effect that the harmonic components lying inside this band will be transferred more or less without blemish and other harmonic components pass with a huge distortion or not at all more in chapter 7 2 1 1 page 67 Bandwidth can be seen as a characteristic of the transmission path given by the range of the signal spectrum The basic rule for the required bandwidth is called Nyquist rate Its definition is that optimal bandwidth equals a half of modulation speed It is true that the necessary bandwidth increases with the amount of transferred information per time unit 3 1 2 Modulation techniques of analog SSTV An SSTV broadcast is usually carried out using single sideband SSB amplitude modulation with a common ham radio transceiver Frequencies above 2 500 Hz are stro
24. We see that more frequent symbols with high probability of occurrence have shorter code than sporadic symbols Our message after encoding 1111011001101001100110010000101 0011001101000110010000101111011 1110110100011110001100110010000 The message length was reduced from 102 to 93 bits For decoding the binary tree on 9 2 can be used again We will start in the root and go along edges 1 1 1 1 0 until we arrive to lead here symbol T then we return to the root and go along 1 1 0 and we arrive to leaf H By this way we continue until the whole message 102 INTRODUCTION TO DIGITAL SLOW SCAN TV 9 is decoded Because Huffman coding is has unique prefires for each code and this prefixes is not start of another codeword the decoding can not do mistake Other compression algorithms using dictionary methods These methods are based on fact that some words in the input file occur more frequently Repeating words are stored in the dictionary These words are replaced with their correspond ing code words in output file Among the representatives of this type of compression belongs LZW Lempel Ziv Welch as used in the ZIP compression or GIF or a variant of the TIFF formats 9 3 3 Lossless data compression Many applications needs for their requirements that data aren t impaired if they are compressed E g for binary programs and data Lossless compression has its justification in the field of computer graphics and image storage too Lo
25. but only in FM channels on VHF The image quality is comparable to the Robot 36 Color mode 4 4 3 Modes MP MR ML These modes were created by Makoto Mori JE3HHT the author of MMSSTV software Some of these modes became quite popular because of the success of MMSSTV The author created modes with both standard and high resolutions They use YCrCb colors and extended VIS code Some modes use a narrower band for syncs and video signals Martin M1 MP115 Figure 4 9 The comparison of modes in real conditions on the 3 7MHz band The change he made to the traditional VIS specification extends the code by 8 extra bits so a 16 bit code is sent instead The first 8 bits LSB are the same for each mode with a value of 35 0x23 that identifies the system While the remaining bits MSB distinguish a particular mode Odd parity is used as a simple check 48 FORMATS OF SLOW SCAN TV TRANSMISSION 4 2300 1900 UD T R e E E S 1500 s 1300 BE 1200 1100 0 200 400 600 800 1000 1200 Time t ms Figure 4 10 The 16 bit VIS code of MP115 mode with a 0x2923 value VIS used in narrowband modes has a very little in common with the original stan dard Initially during vertical synchronization N VIS pulses of 1900Hz and 2300Hz in 100 ms are sent followed by a start bit of 1900 Hz see fig All code bits have a duration of 22 ms
26. de coded A peak power with 100W transceiver is about 20 25 W 9 1 Digital communication basics Before I describe the transmission systems we look at some important concepts of data communication What interests us most is the speed which is possible to transmit information we distinguish between the speed of transmission and modulation Symbol rate v express the number of changes a of carrier signal per second It is measured in unit Baud Bd or Symbols per second S s Symbol rate does not say anything about how much information transmitted on signal carrier Um l a Bd Bit rate v indicates the amount of information transferred per sec ond It is expressed in bits per second bps Bit rate says nothing about how fast the signal carrier changes Up V4 log m bps where m is the number of modulation states We know from previous chapters that an important feature of communication channel is a limited bandwidth B Relation between symbol rate and bandwidth shows Nyquist rate Un 2 B Ideally the symbol rate should be twice the bandwidth Substituting the formula for the symbol rate we get vy 2 B log m 95 9 INTRODUCTION TO DIGITAL SLOW SCAN TV Let s look on the relationship between symbol rate and bit rate because these two term are often use interchangeably E g packet radio on VHF has bit rate 1200 bps and the used modulation is AFSK Audio Frequency Shift Keying Frequencie
27. discrete convolution then 0 1 etc For each pixel is from neighborhood pixels their numerical luminance values multiplied by kernel values added together and resulting value is stored in target image on same position as source Then the matrix moves to next pixel and computation is repeated The target image changes in way defined by values of convolution kernel e g matrix H in fig 13 6 use pixel and its neighborhood of 3 x 3 size and computes weighted mean from these nine pixel with kernel 1 i i git 90 2 75 1 74 ZEETC gt 2 47 4 764 2 754 99 1 51 2 76 1 74 The result is an image smoothing and noise reduction Other matrices are used to increase sharpness edge detection or to create a relief In the GIMP the filter is in menu Filters Generic Convolution Matriz The important parameters are also divisor which adjusts the values in the matrix and offse is used to adjust the colors See fig 13 7 how to set matrix values and parameters Furthermore you can choose the color channels and behaviour of calculation on border pixels it is also possible to determine the divisor and offset automatically 167 13 COMPUTER IMAGE PROCESSING w Convolution Matrix x M Preview Matrix Border d o o o o Extend e a ja s e ow 1 l1 d 0 EEEE os H 6 fo J o 3 Jf Je SCE o jio Jlo Jlo Jfo Divisor 2 offset 128 Normalise
28. fig 9 4 You can notice little distortion for quality about 50 mainly in areas with sharp color gradients Lossy compression of JPEG is not suitable for all types of images It is good for natural images but it is problematic for computer generated graphics like schematic diagrams 3D renders etc where there are many sharp color gradients The example of bad chose of compression see in fig 9 6 The file size of both images is almost same While for lossless PNG we cannot see any distortion in the right image stored in JPEG format with compression set to the closest file size to PNG we see that a DCT transform cannot handle sharp edges and the bias around them makes image heavily distorted There is also an option for storage data in progressive mode In progressive mode in first step the DC coefficients of all image blocks are transferred then first AC co efficients second AC coef etc This allows a low detail preview after receiving only a portion of the data and during a reception more and more details are displayed The progressive mode is very useful for slow DSSTV transfer 106 INTRODUCTION TO DIGITAL SLOW SCAN TV 9 Quality 4096 15 970 B 9 564 B Quality 1096 Quality 396 4 277 B 2474 B Figure 9 4 The file size as result of JPEG compression loss degree Figure 9 5 The detail of image saved in 10 quality 9 3 4 2 JPEG2000 When compared with original JPEG standard the new JPEG2000 has many im
29. help to adjust contrast of image luminace is spread over all range For the result of histogram equalization see pic 13 3 162 COMPUTER IMAGE PROCESSING 13 3500 3000 2500 2000 1500 Number of pixels 1000 500 0 50 100 150 200 250 Pixel intensity Figure 13 2 The image histogram for 256 brigtness values 0 50 100 150 200 250 0 50 100 150 200 250 Figure 13 3 Positive influence of histogram equalization on image contrast In the GIMP the tool for histogram adjustment is in menu Colors Levels In case of low contrast image in pic 13 3 the input levels were set on edges of growing values but the GIMP can make also automatic equalization with dialog 13 4 163 13 COMPUTER IMAGE PROCESSING Adjust Color Levels IS Background 24 lena std low contrast bmp U Presets o Channel Value Reset Channel e Input Levels Adjust Color Curves v Background 32 lenna_bw bmp IR Presets E O Channel Value c Reset Channel RE Deu zs Output Levels jo o 5j 255 All Channels Auto Z Z SIS He CB Edit these Settings as Curves k Sac Smooth Preview M Preview SZM SEE PER Help Reset Cancel ok se Reset Cancel ok Figure 13 4 The second important tool is curve adjustment its the on
30. in high noisy level the reception is impossible The DSSTV traffic can be found on band near the centre of SSTV activity Also hamspirit rules should be observed and we should be considerate to another traffic on the band Sometimes it takes a little tact to explain to uninformed station that the strange rattling sound is the digital signal from your QSO partner A CQ call can be done by sending picture on free frequency HamDRM during transmission broadcast station id so is you don t receive complete data you can see what station is transmitting After the end of transmission you can call the station by voice For reception confirmation or short message transfer there is used waterfall mes sages messages displayed in tuning indicator Principle of these messages is de scribed in next section 10 5 and example of some message see in fig 10 15 Figure 10 15 The confirmation of successful re ception displayed in tuning indicator The reports are same as for the phone operation in the RS readability and strength code The V View value representing image quality of digital transmission is losing 127 10 DSSTV TRANSMISSION SYSTEMS its importance Readability is measured on a scale of 1 to 5 so level 5 stands for for a perfect error free transfer level 4 is 4 still acceptable with occasional failure segments and potentially it s needed to increase the number of instances Report the worst level 1 if can not receive any di
31. in German Darmstadt and then they are processed and they are distributed via EuroBird 9 The Meteosat 9 provides image of Earth globe every 15 minutes the Meteosat 8 sends data every 5 minutes Rapid Scanning Service but only European part of globe is sent In addition to these data via EUMETCAST are broadcast further meteorological products such as NOAA and MetOp HRPT imagery and processed data from other satellite sensors infrared microwaves 11 4 2 Essential Services The unencrypted data from Meteosat 9 and Meteosat 7 are transmitted every six hours also GOES and MTSAT 1R is available every 3 hours Satellite Interval Transmittion times UTC Meteosat 9 HRIT LRIT 6 hours 05 45 11 45 17 45 23 45 Meteosat 7 6 hours 00 00 06 00 12 00 18 00 GOES 9 10 12 MTSAT 1R 3 hours 00 00 03 00 06 00 09 00 12 00 15 00 18 00 21 00 Table 11 2 Essential services data 11 5 Hamradio facsimile operations The facsimile operation did not spread as SSTV in the past years The reason for this is using of complex mechanical scanners and recorders and also a relatively long time of image transfer A little development came with the computer software and cheap interfaces but it is very rare to heard amateur fax on bands The use of facsimile fits for very high resolution images which is better than any SSTV mode The number of lines for image is not given but aspect ratio 4 3 should be used Hamradio op
32. lossless image just choose PNG The algorithm used in PNG is called deflate This method is enhanced in some ways the image lines are firstly processed by filter which tries to find a similar neighborhood for each pixel After processing there is a large number of data with zero value or a value close to zero for same or similar values so compression 103 9 INTRODUCTION TO DIGITAL SLOW SCAN TV algorithms finds in data areas with same value so it can shrinks the length of the resulting file 9 3 4 Lossy compression The principle of lossy compression takes advantage of the processing equipment in the case of the human eye it is unable to process certain information so it actually would be an extra piece of information omitted A widely used method for lossy image compression format is JPEG Joint Pho tographic Experts Group The JPEG is the standard established by the ISO and ITU released in 1992 later upgraded in 1997 A successor is upgraded format JPEG2000 It was developed by JPEG committee since 1995 was released in De cember 2000 and further revised in 2003 but it is not so widespread as its prede cessor 9 3 4 1 JPEG compression JPEG usually does not use RGB color coding but use YCrCb see chapter 3 5 2 because th human eye perceives brightness and colors with different sensitivity The storage of YCrCb colors mostly in the ration 4 2 0 reduces size of file but itself is not enough The image is further tran
33. modulation speed is 45 45 Bd Logic one has 1900 Hz and logic zero 2100 Hz The code word length is 24 bits and it is divided into four groups of 6 bits bits are sent in the following order Each group has the following meaning gt Group 0 5 0 101101 D Group 1 15 10 010101 gt Group 2 25 20 N VIS D Group 3 35 30 010101 xor N VIS For example MP73 N has N VIS 000010 0x02 and the whole code word is 101101 010101 000010 010111 MP modes use the same principle as PD modes The sync takes 9 0 ms followed by a short 1500 Hz gap of 1 0 ms then odd scan line Y brightness is sent followed by the R Y and B Y chrominance signals The chrominance signals are the average of two neighborhood scan lines The scan line is ended by the even Y luminance signal These sequence is repeated 128 x MP modes also have narrowband variants MPxx N and their video signals oc cupy frequencies from 2044 to 2300 Hz The MR and ML modes use YCrCb color coding in 4 2 2 format same as the Robot 72 Color mode Horizontal syncs are same as in MP modes The scan line begins with luminance Y then 0 1 ms gap is sent followed by R Y a gap and B Y the line then ends with a 0 1ms gap These gaps should have the same 49 4 FORMATS OF SLOW SCAN TV TRANSMISSION 2300 pomo jm 3499 iR PARE 7 1500 Frequency f Hz 1200 0 500 10
34. operations to only one user If you have station equipped for satellite communication you can try also SSTV You can also monitor experimental SSTV transmission from International Space Station and receive SSTV signals with your 2m FM transceiver see section 8 6 3 Space communications provides few problems The first of these is Doppler effect named after the famous Austrian physicist which reflects changes in wavelength of the signal between the observer and the signal source on a moving object In practice this means that if the satellite is closer to your position the signal appears to have a shorter wavelength and the receiver must tune to higher frequencies when the satellite is moving away it s exactly the opposite 88 HAM RADIO IMAGE OPERATIONS 8 Other problem is variance of signal quality due to satellite rotation that causes a leakage signal The antenna with circular polarization should be used for these purposes Frequency band Designator 21 30 MHz H 144 146 MHz 435 438 MHz 1 26 1 27 GHz 2 40 2 45 GHz 5 6 GHz 10 4 GHz 24 GHz DIA Sal OI wn oe ci lt 47 GHz Table 8 5 Uplink and downlink bands Frequency bands of linear relays are shown in table 8 5 These frequencies de scribe satellite relay operating modes It is fixed by satellite design on chosen by control center The designator like U V describes uplink 435 438 MHz U and downlink 1
35. the receiver which was turned by the clock machine The picture were printed with fat on a tinfoil sheet Figure 11 1 Bakewell s image telegraph 130 FACSIMILE RADIOFAX 11 A honor for the first fax service however belongs to Giovanni Caselli Italian catholic priest and physicist In 1856 he built device named panthelegraph With pantele graph could be sent images or texts Caselli received enthusiastic support from the French emperor Napoleon III The emperor personally visited his workshop in 1860 and enabled him an access to teleg raphy lines The first commercial fax service started in 1865 in Paris and it was connecting some major cities of France Indeed the transmission was very slow and the fees were high so there was only few clients The service wasn t profitable and had to be stopped In 1901 a German scientist Dr Arthur Korn invented the principle of the pho toelectric reading and began to transfer some positive photographic slides on a transparent substrate These slides were illuminated point by point and row by row and light passed through transparent slide influence the selenium cell The cell changes its resistance depending on the light intensity and transform image pixel shade to electric current The receiver contained light relay a device with early gas discharge lamp The intensity of light exposed present point on photographic paper and it varied according to current flowed form receiver
36. 00 1500 2000 Time ms Figure 4 11 Vertical synchronization and scan line of the MP110 N narrowband mode frequency as the last pixel of the previous color component The MLxx group has a high resolution of 640x496 The MC N modes are narrowband but they use RGB color coding Horizontal pulses last 8 0 ms and are followed by a 0 5 ms gap of 2044 Hz The order of color components is red green blue 4 4 4 Martin HQ The Martin HQ system from Martin Emmerson s workshop was released at the end of 1996 These modes were developed for Robot 1200C SUPERSCAN 2001 and other compatible converters with the EPROM version 4 6 or 1 6 Unlike previous Martin modes they use Y CrCb color coding The transmission time of chrominance signals is half of luminance format 4 2 2 There are 6 signals sent between two doubled syncs The first three signals create an odd scan line luminance Y R Y B Y And the next three signals contain even scan line luminance Y Y R Y B The opposite polarity of chrominace compensates for possible color distortion when signals are not tuned precisely The HQ1 mode has 90 seconds for image transmission and HQ2 has 112 seconds Unfortunately the author refused to disclose the exact specification of the system so this improved system is not commonly found 50 FORMATS OF SLOW SCAN TV TRANSMISSION
37. 00 pixels The speed of transmission is given by rotation of cylinder round per minute rpm and it is equivalent to number of lines per minute lpm Professional stations use most often 120 Ipm in eastern European countries and in post soviet states it is 90 lpm news agencies use 60 lpm and meteo satellites 240 lpm The most common fax images synoptic maps are transmitted only in black and white but some images like retransmission of weather satellite images are in gray scale 134 FACSIMILE RADIOFAX 11 z so e 15 jg if tai is i o i la 4 4 a Ta a x Mini E m P TE SES a 1020 Aaa 1 1025573 5 4 BODENDRUCK GME HPA VI FR 22 07 05 SOUTC PROG VDM 20 07 05 13 UTC 30H z Z DX 7 632885 DEUTSCHER WETTERDIENST b 7 L ol amp hi WO Figure 11 5 Typical synoptic map transmitted on HF by lamie here from station DDH3 line speed 120 lpm and IOC 576 Name IOC lpm APT start d APT stop d Note Wefax 288 288 120 90 60 675 Hz 3s 450 Hz 13s Wefax 576 576 120 90 60 300 Hz 3s 450 Hz 13s Ham Color 204 360 200 Hz 5s 450 Hz 5s color Ham 288b 240 240 120 675 Hz 5s 450 Hz 5s Color 240 288 240 200 Hz 3s 450 Hz 5s color FAX 480 204 480 500 Hz 3s 450 Hz 3s Photopress 352 60 450 Hz T d minimal duration of APT signal Table 11 1 Facsi
38. 03r FEL BEARS SOO Ke eA ESS Broadcast images can contain almost everything do not forget to send your own image or photograph of hamshack your equipment and QTH You can also add descriptive texts It is suitable to get a video digitizer or small webcam and broadcast live images I do not recommend send images which may be distorted during transmission like fractals stereograms and contain a lot of details which is lost due to analog transmission Keep in mind that some picture topics might embarrass your QSO partner Texts in picture should by written by some nice readable font Choose a color that has enough contrast with the image background It is good practice to add contrast edge to letters Note that conditions on the opposite side is not always perfect and it should be hard to decipher small letters in noisy image 81 8 HAM RADIO IMAGE OPERATIONS 8 1 The reporting system The message about report contains info about readability signal strength and picture quality report The report message is transerred as a three letter code RSV Readability Strength Video see table 8 2 Readability shows quality of signal reception in 5 degrees Signal strength describes strength of received signal in 9 degrees Tool to determine the strength is measuring instrument called S meter which is part of most receivers Ab solute deviation of his pointer is not very good indica tion because by the S meter we
39. 040 0 GYA Northwood The United Kingdom 120 576 8 105 0 SVJ4 Athens Greece 120 576 08 45 10 44 8 121 9 BAF36 Beijing China 120 576 8 140 0 BMF Taipei China 120 576 8 146 6 IMB55 Roma Italy 120 576 8 457 8 VFA Inuvik Canada 120 576 02 00 16 30 8 459 0 NOJ Kodiak Alaska USA 120 576 8 461 9 3SD Beijing China 120 576 8 467 5 JJC Kyodo News Agency Japan 60 576 meteo maps 120 Ipm 8 503 9 NMG New Orleans Louisiana USA 120 576 8 677 0 CBV Valparaiso Playa Ancha Chile 120 576 8 682 0 NMC Pt Reyes California USA 120 576 9 110 0 NMF Boston Massachusetts USA 120 576 9 165 0 HLL4 Seoul Republic of Korea 120 576 158 LIST OF PROFESSIONAL STATIONS 12 Freq Ident Station Ipm IOC Note kHz Call sign 9 459 0 ZKLF Wellington New Zealand 120 576 9 982 5 KVM70 Honolulu Hawaii USA 120 576 05 19 15 56 10 116 9 BAF4 Beijing China 120 576 10 536 0 CFH Halifax Nova Scotia Canada 120 576 10 555 00 VMW Wiluna Australia 120 576 10 980 01 RCC76 Moscow Russia 90 120 576 IOC 288 10 980 00 RCC76 Moscow Russia 90 120 576 IOC 288 11 030 0 VMC Charleville Australia 120 576 11 086 5 GYA Northwood The United Kingdom 120 576 06 00 20 00 11 090 00 KVM70 Honolulu Hawaii USA 120 576 11 420 0 BDF Shanghai China 120 576 12 412 5 NOJ Kodiak Alaska USA 120 576 12 745 5 JJC Kyodo News Agency Japan 60 576 meteo maps 120 lpm 12 750 0 NMF
40. 048 pixels per second in binary notation this gives a nice rounded number The other two modes have somewhat atypical resolutions in comparison with other SSTV modes but these resolutions are normal system resolutions on Amiga computers It is AVT 94 with 320x200 and AVT 188 with the same line speed but twice the scan lines 320x400 The image is displayed in an aspect ratio of 4 3 in both cases For some SSTV systems scan converters the detection of vertical sync is a must So the VIS code is repeated three times for accurate reception VIS is necessary for image reception when no line sync is sent and later synchronization is not possible The original AVT software however does not need to receive VIS but relies more on the digital header After a series of VIS code there is a digital header see fig 4 7 which contains synchronization data It is a sequence of 32 frames of 16 bits Each frame contains only 8 bits of information but it is sent twice first in normal form and second inverted Normal and inverted parts can be compared for error detection Each 40 FORMATS OF SLOW SCAN TV TRANSMISSION 4 frame starts with a 1900Hz pulse while data modulation uses 1600 Hz for the rep resentation of logical zeros and 2200 Hz for logical ones Narrow band variants use 1700 Hz for zeros and 2100 Hz for ones Both variants use a modulation speed of exactly 2048 20 102 4 Bd so the data pulse has a length of 9 766 ms TUE
41. 15 140 256 320 109 389 MC180 N RGB 0x16 180 256 320 85 167 MP73 YCrCb 0x25234 73 256 320 210 526 MP115 YCrCb 0x29234 115 256 320 133 038 MP140 YCrCb 0x2a234 140 256 320 110 092 MP175 YCrCb 0x2c23 175 256 320 87 591 MP73 N YCrCb 0x02 73 256 320 210 526 MP110 N YCrCb 0x04 115 256 320 139 860 MMsSTrv MP140 N YCrCb 0x05 140 256 320 110 092 MR73 YCrCb 0x45234 73 256 320 419 141 MR90 YCrCb 0x46234 90 256 320 340 619 MR115 YCrCb 0x49234 115 256 320 266 489 MR140 YCrCb 0x4a239 140 256 320 218 858 MR175 YCrCb 0x4c232 175 256 320 175 362 MR180 YCrCb 0x85231 180 496 640 330 306 MR240 YCrCb 0x86234 240 496 640 248 293 MR280 YCrCb 0x89234 280 496 640 212 277 MR320 YCrCb 0x8a234 320 496 640 185 960 TV 1 RGB 104 320 256 320 84 383 MSCAN TV 2 RGB 105 320 256 320 134 530 P3 RGB 113 203 496 640 146 565 Pasokon P5 RGB 114 305 496 640 97 710 PT RGB 115 406 496 640 13 282 PD 50 YCrCb 93 50 256 320 309 151 PD 90 YCrCb 99 90 256 320 170 687 PD 120 YCrCb 95 126 496 640 235 997 PD PD 160 YCrCb 98 161 400 512 149 177 PD 180 YCrCb 96 187 496 640 159 101 PD 240 YCrCb 97 248 496 640 120 000 PD 290 YCrCb 94 289 616 800 128 030 Proskan J120 RGB 100 120 240 320 128 046 54 LIST OF SSTV MODES 5 System Mode Colors VIS code Duration s Lines Columns lpm Color 12 YCrCb 0 12 120 160 600 000
42. 3 6 Decomposition of colour image to basic components 3 5 Colour transmission 3 5 1 Additive colour model Every colour can be decomposed into three primary colours red green and blue The additive colour model produces other colours by combining these three primary colours During image transmission the image is decomposed into these independent colour components on the transmitting side Then they are gradually transferred and on the receiving side the components are re composed into a colour image If it is possible to detect about 64 frequency levels in the 800 Hz video channel then each colour component contains 64 brightness levels And the resulting colour image then contains 64 x 64 x 64 256144 colours If a demodulator can distinguish 256 levels it is possible to transfer over 16 millions 256 colours Colour SSTV transmission can meet the most demanding requirements of colour depth Some colour SSTV systems also use a property of human vision which is a different sensitivity to the primary colour components In this case the image scan lines are not divided into three equal parts for each colour component Because the eye is most sensitive to green the largest part of the line takes just this part and the remainder are filled with red and blue parts For example the ratio is 4 2 2 for G R B 20 MODERN SSTV FEATURES 3 f kHz Figure 3 7 Decomposition of colour image into RGB signals The addi
43. 3 7MHz band Line syncs and inner scan line gaps have a similar duration at all four speeds but the number of lines and horizontal resolution for each mode is different Al though the syncs aren t necessary for transmission they are still transmitted at the beginning of each scan line in order to synchronize the converter at any time during the reception It is important because it consumes a lot of broadcast time and the station does not have to wait for the start of a new frame but a receiver can get synchronization at any time during transmission The Martin system allows us to work with four different modes speeds The most popular version is the Martin M1 with 256 lines per frame in two minutes Other modes of the Martin system have either half the line or half the horizontal resolution of the best quality M1 The mode M4 has the lowest quality and 128 lines Modes Martin M1 and M2 are often used between European stations 37 4 FORMATS OF SLOW SCAN TV TRANSMISSION Mode Transfer Color Scan line ms Speed Resolution name time sequence Sync G B R Ipm Martin M1 114s 320x256 G B R 4 862 146 432 146 432 146 432 134 3947532 Martin M2 58s 160x256 G B R 4 862 13 216 13 216 73 216 264 5525975 Martin M3 57s 320x128 G B R 4 862 146 432 146 432 146 432 134 3947532 Martin M4 29s 160x128 G B R 4 862 13 216 13 216 73 216 264 5525975
44. 4 190736 00 SPC PROGNOSIS T 72 1936 122 SFC PROGNOSIS T472 zm 10748 00Z SFC PROGNOSIS T 96 1948 122 SFC PROGNOSIS T 96 0800 00Z SFC PROGNOSIS T 120 2000 122 SFC PROGNOSIS T 120 10812 002 THICKNESS GPH ANALYSIS 2012 12 THICKNESS GPH ANALYSIS m 10824 002 SIG WINDS T 48 2024 122 SIG WINDS T 48 m 10836 00Z SIG WINDS T 72 2036 122 SIG WINDS T 72 0848 DOZ SIG WINDS T 96 2048 122 SIG WINDS T 96 150900 062 SFC ANALYSIS 2100 18Z SFC ANALYSIS 10912 002 THICKNESS GPH ANALYSIS 2112 122 THICKNESS GPH ANALYSIS m 10924 002 THICKNESS GPH T 24 2124 122 THICKNESS GPH T 24 9936 002 850MB SPOT WINDS 7424 2136 122 850MB SPOT WINDS T 24 0948 00Z 700MB SPOT WINDS T 24 2148 122 700MB SPOT WINDS T 24 11000 06Z SFC ANALYSIS 2200 18Z SFC ANALYSIS 11012 062 SFC PROGNOSIS T 24 2212 182 SFC PROGNOSIS T 24 1024 06Z REDUCED VIS T 24 2224 18 REDUCED VIS T 24 11036 062 850MB WBPT PPTN T 24 2236 182 850MB WBPT PPTN T 24 11048 06Z OAT AND TD CONTOUR T 24 2248 18Z OAT AND TD CONTOUR T 24 11100 062 SFC ANALYSIS 2300 182 SFC ANALYSIS 1112 062 SFC PROGNOSIS T 24 2312 18Z SFC PROGNOSIS T 24 11124 062 SEA AND SWELL T 24 2324 182 SEA AND SWELL T 24 11136 002 THICKNESS GPH T 24 2336 122 THICKNESS GPH T424 m 11148 00Z GALE WARNING SUMMARY 2348 122 GALE WARNING SUMMARY Fas E FREQS a a m p 2618 5KBZ 4610 OKEZ W8040 0KHZ _ m 8110885 5KHZ m Figures 11 1 6 The station schedule of GYA 136 FACSIMILE RADI
45. 44 146 MHz V E g Fuji OSCAR 29 FO 29 operates in mode V U the uplink is in the range of 146 000 to 145 900 kHz CW LSB and downlink 435 800 to 435 900 kHz CW USB Note that relay inverts signal frequency LSB to USB Other satellites carry on board the single channel FM transmitter such as the pop ular AO 27 with uplink 145 850 kHz FM and downlink 436 795 kHz FM It is required to monitor own SSTV signals on downlink when working on linear relays Some sound cards support full duplex operation so the computer can also send and receive in same time Then the operator changes the transmit frequency so that receiving frequency appears to be same just follow the position of the syncs on spectroscope This way compensates the Doppler effect During years there were many satellites used for SSTV operations like FO 29 VUSat OSCAR 52 beacon 145 936 kHz AO 51 SO 50 etc But satellite lifetime is limited in time board batteries getting weaker and ground control center switching off transponder and waits for their recharge from solar panels You can find actual informations and satellite statuses on website of Amateur Satellite Corporation i e AMSAT 89 8 HAM RADIO IMAGE OPERATIONS http www amsat org 8 6 1 SSTV from Mir station Days of the orbital station Mir are already numbered but as a reminder there is description of the experiences with SSTV transmission which took place in Manned Amateur Radio Experiment MAREX i
46. 45 05 00 Broadcast time 00 00 04 00 09 00 16 00 21 00 23 00 beginning every whole hour 12 6 4 Honolulu Hawaii USA Ident Frequency lpm IOC Power Note KVM70 9 982 5 kHz 120 576 5 kW 05 19 15 56 KVM70 11 090 0 kHz 120 576 5 kW KVM70 16 135 0 kHz 120 576 5 kW 17 19 03 56 Broadcast time continuous by frequency 156 LIST OF PROFESSIONAL STATIONS 12 12 7 List by frequency Freq Ident Station Ipm IOC Note kHz Call sign 122 5 CFH Halifax Nova Scotia Canada 120 576 148 0 Pevek Chukotka peninsula 90 576 2 054 0 NOJ Kodiak Alaska USA 120 576 2 618 5 GYA Northwood The United Kingdom 120 576 20 00 06 00 2 628 0 VMC Charleville Australia 120 576 09 00 19 00 3 241 0 BDF Shanghai China 120 576 3 247 4 ZKLF Wellington New Zealand 120 576 09 45 17 00 3 253 0 VFF Iqaluit NWT Canada 120 576 21 00 23 30 3 253 0 VFR Resolute NWT Canada 120 576 00 10 09 00 3 585 0 HLL1 Seoul Republic of Korea 120 576 3 622 5 JMH Tokyo Japan 120 576 3 830 0 Moscow Russia 90 120 576 IOC 288 3 855 0 DDH3 Hamburg Pinnenberg Germany 120 576 4 228 0 CBV Valparaiso Playa Ancha Chile 120 576 4 235 0 NMF Boston Massachusetts USA 120 576 02 30 10 28 4 271 0 CFH Halifax Nova Scotia Canada 120 576 4 298 0 NOJ Kodiak Alaska USA 120 576 4 316 0 JJC Kyodo News Agency Japan 60 576 meteo maps 120 lpm 4 317 9 NMG New Orleans Louisiana USA 120 576 4 346 0 NMC Pt Reyes Califo
47. 82 12786 17151 2 22527 NE GOES IR NMC 8682 12786 17151 2 22527 Pacific GOES IR NMF 4235 6340 5 9110 12750 CBV 4228 8677 17146 4 139 11 FACSIMILE RADIOFAX UTC Station Ident Frequencies kHz Note 17 06 Alaska USA NOJ 2054 4298 8459 12412 5 GOES IR 18 35 Hawai USA KVM70 9982 5 11090 16135 East pacific GOES IR 18 49 Hawai USA KVM70 9982 5 11090 16135 SW pacific GOES IR 19 02 California USA NMC 8682 12786 17151 2 22527 Tropical GOES IR 19 10 Tokyo Japan JMHx 3622 5 7795 13988 5 MTSAT 19 20 Taipei China BMF 4616 8140 13900 18560 GMS 19 30 Playa Ancha Chile CBV 4228 8677 17146 4 20 00 Lousiana USA NMG 4317 9 8503 9 12789 9 17146 4 Tropical GOES IR 21 00 Hawai USA KVM70 9982 5 11090 16135 Pacific GOES IR 21 13 California USA NMC 8682 12786 17151 2 22527 Pacific GOES IR 21 43 Hawai USA KVM70 9982 5 11090 16135 Tropical GOES IR 21 51 Massachusetts USA NMF 4235 6340 5 9110 12750 23 17 Alaska USA NOJ 2054 4298 8459 12412 5 GOES IR 23 25 Playa Ancha Chile CBV 4228 8677 17146 4 It depends on your own position if you have interest in reception of images from these stations For long distance stations should not be reception conditions so good every day Their images for me in Europe is not interesting for weather forecast but there are images of hurricanes typhoons and other unusual weather phenomena 11 4 1 Meteorologic satellites If you are interest
48. 995 Montalbano John KA2PYJ The ViewPort VGA Color SSTV System 73 Aug 1992 Nozdrovicky L Z klady telev zie Slovensk vydavate stvo technickej literat ry 1962 Null Linda Lobur Julia The Essentials of Computer Organization and Architecture Jones and Bartlett Publishers 2003 Nov sm ry v SSTV Amat rsk r dio vol 7 8 1986 Pagel Paul N1FB Radioware SSTV Explorer QST Apr 1994 Pitt Doug Basic NBTV Techniques 1998 Prinz Richard OE1RIB Kamera Shield auf Arduino Basis f r ein SSTV Sendemodul Funka mateur vol 10 2012 Prosise Jeff Bitmapov soubory pohled dovnit PC Magazine nor 1997 Ramon Carine ON7LX HF Managers Handbook IARU 2003 Rensen Marius HF FAX Station List 2002 Schick Martin K KA4IWG Color SSTV and the Atari Computer QST Aug 1985 Seger Ji Jak se lid dorozumivali Albatros 1987 Taggart Dr Ralph E WB8DQT A New Standard for Amateur Radio Fascimile QST Feb 1993 Taggart Dr Ralph E WB8DQT Digital Slow Scan Television QST Feb 2004 Taggart Dr Ralph E WB8DQT The ARRL Image Communications Handbook ARRL 2002 Taggart Dr Ralph E WBSDQT The Romscanner QST Mar 1986 U S Department Of Commerce Worldwide Marine Radiofacsimile Broadcast Schedules NOAA 2010 Vester Ben K3BC An Inexpensive SSTV System QST Jan 1994a Vester Ben K3BC An Inexpensive SSTV System continues to Grow QST Dec 1994b Vit V Televizn technika b
49. Boston Massachusetts USA 120 576 14 00 22 28 12 786 0 NMC Pt Reyes California USA 120 576 12 789 9 NMG New Orleans Louisiana USA 120 576 12 831 9 3SD Beijing China 120 576 13 510 0 CFH Halifax Nova Scotia Canada 120 576 13 538 0 ZSJ Cape Naval South Africa 120 576 13 550 5 ZKLF Wellington New Zealand 120 576 13 570 0 HLL5 Seoul Republic of Korea 120 576 13 597 00 JMH4 Tokyo Japan 120 576 13 597 4 MB56 Roma Italy 120 576 13 882 5 DDK6 Hamburg Pinnenberg Germany 120 576 13 900 0 BMF Taipei China 120 576 13 920 0 VMC Charleville Australia 120 576 14 366 9 BAF8 Beijing China 120 576 14 436 0 GYA Northwood Persian Gulf Base 120 576 nep etr it provoz 14 842 00 ATP65 New Delhi India 120 576 02 30 14 30 15 015 00 VMW Wiluna Australia 120 576 16 025 9 BAF9 Beijing China 120 576 159 12 LiST OF PROFESSIONAL STATIONS Freq Ident Station lpm IOC Note kHz Call sign 16 035 0 9VF 252 Kyodo News Agency Singapore 60 576 07 40 10 10 14 15 18 15 16 135 0 KVM70 Honolulu Hawaii USA 120 576 117 19 03 56 16 340 1 ZKLF Wellington New Zealand 120 576 21 45 05 00 16 903 9 3SD Beijing China 120 576 16 971 0 JIC Kyodo News Agency Japan 60 576 meteo maps 120 lpm 17 069 6 JIC Kyodo News Agency Japan 60 576 meteo maps 120 lpm 17 146 4 CBV Valparaiso Playa Ancha Chile 120 576 17 146 4 NMG New Orleans Louisiana USA 120 576 12 00
50. C ADXA CQ DX Award and many more can be obtained with indication of used communication mode and some additional variants like QRP There are few diplomas for exclusive two way QSO using slow scan television listed bellow 8 3 1 IVCA DX Achievement Award DXAA The award is issued to amateurs and listeners for two way SSTV contact recep tion with 50 countries from DXCC list Additional stickers are for every more 25 countries 8 3 2 DANISH DX SSTV AWARD The award can be obtained by radio amateurs and listeners for confirmed contacts with 50 different ARRL s DXCC countries A QSL list must contain call time date band mode SSTV and country and confimed by two licensed amauteurs and signed by applicant All bands legally used in applicant s country are accepted but no contacts via repeaters It is possible to get additional stickers for contacts with 100 countries and 1 OZ station silver 150 2 gold and 200 diamant The fee for basic award is 8 or 10 Award manager S K Mogensen OZ6SM Rundhgjvej 8 DK 7970 Redsted Dan mark email oz6sm nypost dk http www ddxg dk awards sstvaward htm 8 3 3 Russian SSTV Award This award is sponsored by the CRC of Krenkelya and the Moscow section SSTV to popularize the use of SSTV in Russia and other countries of the CIS Earn 75 points by contacting Russian and CIS stations on the SSTV mode on or after 1 March 84 HAM RADIO IMAGE OPERATIONS 8 1998 Contacts with mem
51. C 1 mode is the 24s mode with 128 lines so the image quality is not better than the 8s mode but the colors improve the picture The system was soon upgraded for modes with longer transmission First the number of lines was doubled to 256 and the transfer extended to 48 seconds The last SC 1 96s mode has better horizontal resolution for good image quality The professional converter Wraase Electronics SC 1 was most popular in Germany but its market share was lower in comparison to the Robot converters produced in the same period 4 2 2 Robot color system The Robot modes are named according to the converters in which they were im plemented They are scan converters Robot 400C 450C and 1200C They were produced in San Diego by Robot Research Inc 32 FORMATS OF SLOW SCAN TV TRANSMISSION 4 Mode Transfer Color Scan line ms Speed Resolution name time sequence Sync G B R 1pm Wraase SC 1 24 Color 24 s 128x128 G B R 6 0 54 0 54 0 54 0 333 3 Wraase SC 1 48Q Color 48s 256x128 G B R 6 0 108 0 108 0 108 0 175 4 Wraase 5C 1 48 Color 48 s 128x256 G B R 6 0 54 0 54 0 54 0 333 3 Wraase SC 1 96 Color 96 s 256x256 G B R 6 0 108 0 108 0 108 0 175 4 Table 4 2 The Wraase SC 1 scan line timing They do not use RGB color coding as SC 1 but YCrCb Scan lines consist of a luminance signal Y followed by differential chrominance signals R
52. Color 24 YCrCb 4 24 120 160 300 000 Color 36 YCrCb 8 36 240 320 400 000 Robot Color 72 YCrCb 12 72 240 320 200 000 B amp W 8 BW 128 8 160 120 900 000 B amp W 12 BW 5 6 Y 12 320 240 600 000 B amp W 24 BW 9 10 11 24 320 240 300 000 B amp W 36 BW 13 14 15 36 320 240 200 000 S1 RGB 60 110 256 320 140 115 S2 RGB 56 71 256 320 216 067 Scottie 93 RGB 52 55 128 320 140 115 S4 RGB 48 36 128 320 216 067 DX RGB 76 269 256 320 57 127 Scottie DX2 RGB 80 136 256 320 112 905 SP 17 BW BW 125 17 256 128 895 520 Vester RGB 86 414 480 512 74 832 Color FAX 8 BW 17 18 19 8 120 128 11000 000 16 BW 21 22 23 16 120 256 500 000 24 BW 25 26 27 24 256 128 930 520 Wraase SCI 32 BW 29 30 31 32 240 256 500 000 24 RGB 16 24 128 128 900 000 48 RGB 20 48 128 256 489 102 48Q RGB 24 48 256 128 900 000 96 RGB 28 96 256 256 500 000 30 RGB 51 30 128 320 249 595 Wraase SC2 60 RGB 59 60 256 320 249 600 120 RGB 63 120 256 320 126 175 180 RGB 55 180 256 320 84 383 Notes a VIS code order Normal Narrow mode QRM mode Narrow QRM gt b Scottie DX and AVT 188 were created at the same time and accidentally share the same VIS code c VIS codes for each color component red green blue The green component is comonly used for BW images d Uses 16 bit VIS see sec 4 4 3 55 5 LIST OF SSTV MODES e Uses another digital code N VIS see sec 4 4 3 gt f Uses odd parity 56 SSTV Equ
53. Dr Korn designed the first phototelegraph device in 1902 and already in March 1904 he managed to reproduce photo transfered form Munich to Nuremberg The transfer of postcard size photo took 24 minutes In 1907 major cities Berlin Munich Paris and London were linked and his devices were bought by newspaper agencies and the first phototelegraphic service was founded The transfer was simplified by using of an electric photocell Thanks to the photocell the transfer speed increased and the preparation of transparent slides wasn t necessary The photocell is so sensitive that it is influenced by reflected light and some photos could be scanned directly The photocell was used for the first time by American captain Richard H Ranger for test transmission between Cleveland and New York In November 30th 1924 was wirelessly transfered photo of the British royal couple from London to New York The first phototelegraphic service between America and Europe was established in May 1st 1926 11 2 The fax mode The modern facsimile fax is used for transmitting images in the high resolution usually 1810 dots per line with image size up to several thousand lines An rela tively long time of transmission is used due to small bandwidth In dependency on image size and transmission speed it takes from 3 to 20 minutes 131 11 FACSIMILE RADIOFAX 11 2 1 Image transmission A typical mechanical transmitter consist of cylinder rotated by crystal c
54. Gaussian Blur it can filter continuous areas and edges leaves unaffected but for received images is not suitable 169 13 COMPUTER IMAGE PROCESSING 13 3 2 2 Median filter The term median is the middle value in list of numbers here luminance values The image filter works with pixel neighborhood e g with 3 x 3 size then sort their values and takes the median i e middle value of the sequence Pixels 21 22 20 21 19 231 19 21 20 21 22 20 Sorted 19 19 20 20 21 21 21 22 231 21 19 231 Average 43 Median 21 19 21 20 Table 13 1 none We see that if we use the averaging then significantly skewed value 231 which can be caused by noise greatly affects the result In contrast the median is not influenced by extreme deviations The disadvantage of median filtering is that it sometimes distorts the thin lines and sharp gradient in the image Median 3 x 3 Median 5 x 5 Figure 13 9 The results of noise reduction with median filter 170 COMPUTER IMAGE PROCESSING 13 In GIMP the median filter is in Filters Enhance Despeckle There are several options for filter settings The radius from 1 for 3 x 3 neighborhood to 20 for 41 x 41 and the black level 1 255 and white 0 256 The pixels darker or brighter than these two levels will be removed filter passes every level for the extreme values and 256 Moreover it is still possible to select adaptive median when GIMP tries to determin
55. ISSION SYSTEMS signal consist of two tones 1180 and 1520Hz These frequencies are labeled on spectroscope so you can fine tune and align the frequency peeks with the marks ROET Tune Fa _OK2MNM Tunning signal Spectroscope with and station id data transmission Figure 10 6 The tuning spectrospoce in DIGTRX Following operations must be done for transmission and reception of images 1 Original data file is processes in case of images the resolution and compression level are set Then is generated WAV audio file which contains a audio signal for radio transmission The time spent to signal generation is derived from input file size and computer configuration It can took form a second or two 2GHz and faster CPUs up to several minutes on slower systems 400 MHz 2 The audio file is played and transmitted The reception station records sound and store it on a hard drive 3 The software process recorded WAV file and reconstructs original file This step is also computationally very demanding and the time needed for decoding depends not only on the volume of data and processor speed but also on how much is necessary to use the error correction algorithm This step may take several minutes on a slow computer on a 2GHz machine it takes 15 seconds Barry Sanderson KBAVAK developed programs for RDFT encoding These pro gram are command line driven and it is available as open source under GNU GPL license So p
56. Ident Frequency lpm IOC Power JJC JJC JJC JJC JJC JJC 4 316 0 kHz 8 467 5 kHz 12 745 5 kHz 16 971 0 kHz 17 069 6 kHz 22 542 0 kHz 60 60 60 60 60 60 516 516 576 576 576 576 5 kW meteo 10 kW meteo 15 kW meteo 15 kW meteo 15 kW meteo 15 kW meteo 151 Note maps 120 Ipm maps 120 Ipm maps 120 Ipm maps 120 Ipm maps 120 Ipm maps 120 Ipm 12 LIST OF PROFESSIONAL STATIONS Broadcast time 01 45 07 45 11 00 11 30 13 35 22 15 12 3 11 Kyodo News Agency Singapore Ident Frequency lpm IOC Power Note 9VF 252 16 035 0 kHz 60 576 10 kW 07 40 10 10 14 15 18 15 9VF 252 17 430 0 kHz 60 576 10 kW 07 40 10 10 14 15 18 15 Broadcast time 07 40 10 10 14 15 18 15 12 3 12 Northwood Persian Gulf Base Ident Frequency lpm IOC Power Note GYA 6 834 0 kHz 120 576 10 kW 18 00 08 00 GYA 14 436 0 kHz 120 576 10 kW nep etr it provoz GYA 18 261 0 kHz 120 576 10 kW 08 00 18 00 12 4 South America 12 4 1 Rio de Janeiro Brazil Ident Frequency lpm IOC Power Note PWZ 33 12 665 0 kHz 120 576 1 kW PWZ 33 16 978 0 kHz 120 576 1 kW Broadcast time 07 45 08 50 16 30 17 35 12 4 2 Valparaiso Playa Ancha Chile Ident Frequency lpm IOC Power Note CBV 4 228 0 kHz 120 576 1 kW CBV 8 677 0 kHz 120 576 1kW CBV 17 146 4 kHz 120 576 1 kW Broadcast time 11 15 23 25 152 LIST OF PROFESSIONAL STATIONS 12 12 5 North America 12 5 1 Halifax Nova Scotia Canada Ident Frequency Ipm IOC P
57. MARTIN BRUCHANOV OK2MNM Image Communication on Short Waves www sstv handbook com Contents 1 Preface 2 Slow scan television 24 2 The beginnings Image transmission 3 Modern SSTV features 3 1 3 1 1 31 2 3 2 3 3 3 4 3 5 3 5 1 3 5 2 3 6 3 6 1 3 6 2 3 6 3 Signal modulation Bandwidth Modulation techniques of analog SSTV Image resolution Line speed Black amp white transmission Colour transmission Additive colour model Composite colour model Synchronization Horizontal synchronization Vertical synchronization VIS code Additional synchronization data 4 Formats of slow scan TV transmission 4 1 4 1 1 4 1 2 4 2 4 2 1 4 2 2 4 2 3 4 2 4 4 2 4 1 4 2 5 4 2 6 4 3 4 3 1 4 3 2 4 3 3 Black and white SSTV systems Modes for digital converters BW transmission with computer software Color SSTV modes Wraase SC 1 Robot color system The Martin synchronous system Scottie Scottie DX special mode for long distance transfers Amiga Video Transceiver Wraase SC 2 High resolution transmission FAX480 Pasokon TV PD modes 12 13 13 14 15 16 16 20 20 21 24 24 24 25 28 28 28 29 30 32 32 35 38 39 39 43 44 44 45 46 4 4 Experimental modes 4 4 1 MSCAN TV 4 4 2 Kenwood FAST FM 4 4 3 Modes MP MR ML 4 4 4 Martin HQ 5 List of SSTV modes 6 SSTV Equipment 6 1 Transceiver 6 2 Station equipment for visual communication 6 3 Historical tidbits 5 0 1 SSTV monito
58. OFAX 11 For first experiments with facsimile reception are suitable strong local stations Here in Europe it is the German station DDHx which is active on frequencies 3855 0 7880 0 a 13882 5 kHz As already announced station always receive in USB mode and tune it 1900 Hz below Therefore DDH3 tune on 3853 1 kHz Its speed is 120 lpm and IOC 576 TIZL EDW Figure 11 7 Test chart of DDH3 transmitted daily in 11 10 UTC Another station is an Englich GYA broadcasting from Northwood 120 576 on frequencies 2618 5 4610 0 8040 0 11085 5 kHz active are at least two channels simultaneously From long distance stations cab be received almost daily Tokyo station JMH4 Of the three transmitters is the best JMH4 on 13597 0 kHz with 5 kW output power Besides the usual synoptic chart there are available satellite imagery too TOKYO JAPAN RE 2822 5KHZ Cr L y ARRR ld x KR RR Figure 11 8 Test chart from JMHA available daily at 13 00 UTC Next Tokyo station is JJC it is Kyodo News Agency Transmission speed is 601pm and IOC 576 sometimes 1201pm when weather charts are posted The station broadcast simultaneously on several frequencies 12745 5 16971 0 17069 6 22542 0 kHz by listening find the active frequency Interestingly the owner of JJC station was 137 11 FACSIMILE RADIOFAX in 1997 thinking about closure if they find some other way for news distribution It didn t sto
59. ONS 7 Reception from TRX Line In Microphone Transmission to TRX gt Line Out Speaker Out Figure 7 6 Basic interface between transceiver and sound card fii Master Volume EN zj x Options Help Master Volume Wave SW Synth CD Player Line In Balance Balance Balance Balance Balance amp J 4 e J 4 amp J 4 amp J 8 amp H d Volume Volume Volume Volume Volume T T T S E S Mute all Mute Mute Mute Mute SoundMAX HD Audio Figure 7 7 Software volume control After the audio mixer configuration it is useful to save your sound card settings you can restore it every time before operations A program QuickMiz is can easily store your settings because some other program can change it http quickmix softpedia com 71 7 COMPUTER OPERATIONS 7 2 4 PTT control The PTT Push To Talk button switch between reception and transmission For its control there are several possibilities 1 Manual PTT switching This handy method is not very elegant but for the first experiments can be used 2 Automatic switching can provide TRX with a VOX feature when the TRX is automatically keyed by signal in the input An disadvantage of this method may be that its reaction is not immediate so in case of digital modes the beginning states of transmission or SSTV vertical synchronization can be lost Keep in ming that operating system often produc
60. Pasokon TV Slow Scan TV Interface 73 Amateur Radio Today July 1995b Glanc Antonin OK1GW Amat rsk televize Amat rsk radio vol 6 7 8 1971 Glidden Ramon L W5NOO Getting Started with Slow Scan Television QST Sep 1997 GNU Image Manipulation Program User Manual Gola Miroslav ing OK2UGS P ij ma faksimile v pismu KV 40 Praktick elektronika A Radio vol 4 5 1999 Goodman Dick WA3USG SSTV with the Robot 1200C Scan Converter and the Martin Emmerson EPROM Version 4 0 73 Amateur Radio Today Jul 1991 Harlan Gene WB9MMM Slow Scan TV with the Sound Blaster QEX May 1993 Hioki Takashi JF1GUQ Pasokon TV Mobile Ham Amateur Radio Magazine Feb 1993 174 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 4T 48 49 50 51 52 53 54 55 56 57 58 59 61 Hubenak Ji RNDr Za zen pro p jem faksimile po ta em PC AT Amat rsk R dio vol 6 1994 Jordan Karel Ing Radioamat rsk dru ice st edn rada radioklubu Svazarmu 1983 Karmasin Karel OK2FD SSTV a PC AMA magaz n duben 1997 Langner John WB2OSZ SSTV The AVT System Secrets Revealed CQ TV vol 149 1990 Langner John WB2OSZ Slow Scan Television It isn t expensive anymore QST Jan 1993 Langner John WB2OSZ Color SSTV for the Atari ST 73 Amateur Radio Dec Jan 1989 1990 Langner John WB2OSZ Slow Scan TV Questions and Answers Radio Fun Feb 1
61. R G B 8 0 180 0 180 0 180 0 109 389243 MC180 N 180s 320x256 0x16 R G B 8 0 232 0 232 0 232 0 85 166785 Table 4 10 The parameters of MMSSTV modes 51 FORMATS OF SLOW SCAN TV TRANSMISSION Frequency f Hz 2300 T 1900 1500 1200 0 100 200 300 400 500 600 700 800 900 Time ms Figure 4 12 Two scan lines of Martin HQ modes when color bars are sent 52 List of SSTV modes System Mode Colors VIS code Duration s Lines Columns lpm AVT 24 RGB 64 65 66 67 31 128 128 960 000 l AVT 90 RGB 68 69 70 71 98 240 256 480 000 Amiga Video AVT 94 RGB 72 73 74 75 102 200 320 384 000 Transceiver AVT 188 RGB 76 77 78 79 196 400 320 384 000 AVT 125 BW BW 80 81 82 83 133 400 320 192 000 FA X480 BW 85 138 480 512 224 497 FAST FM YCrCb 904 13 240 320 1118 881 MI RGB 44 114 256 320 134 395 M2 RGB 40 58 256 320 264 553 Martin M3 RGB 36 57 128 320 134 395 M4 RGB 32 29 128 320 264 553 HO YCrCb 41 90 240 320 85 055 Martin HQ HQ2 YCrCb 42 112 240 320 68 680 53 LIST OF SSTV MODES System Mode Colors VIS code Duration s Lines Columns lpm MC110 N RGB 0x14 110 256 320 137 143 MC140 N RGB 0x
62. RS232 interface Some programs also support similar switching circuit as described before but on parallel port LPT 7 2 5 Eliminate supply noise A computer and a TRX can have slightly different electrical potential and in this case the direct connection causes annoying noise in communication channel It is possible to remove noise witch galvanic separation of both devices The path of 72 COMPUTER OPERATIONS 7 audio signal should go throught galvanic transformer and PTT control switch with opto isolator e g 4N25 4N33 etc Maybe you will need to change R2 to lower value when the opto isolator is not switched properly when serial port signal is on T1 1 1 O 1 5 e O 2 6 TRX GND PC GND 12 1 1 O wi 28 Line Out TX O 2 6 TRX GND PC 6 BTT 1N4004 OK1 L A e COM TRX GND p DTR 4 PC GND Figure 7 8 The galvanic separation of transceiver and sound card 7 3 Timing oscillator configuration There is description of synchronous free run SSTV system in section 3 6 1 Hori zontal synchronization pulses syncs are detected only at the beginning of reception and after synchronization a reception device stops detect syncs and receive with free run scan Due to this there are excessive requirements for accurate timing of corresponding stations If the timing slightly differs then images are distorted inaccurate timing causes image slant You can see i
63. Resolution test 20 Photography 10 at 0 M k Hy a EMP Z D PCM TW TU E 20 Yi i dli E u M Mw muU ii l W 60 70 0 1000 2000 3000 4000 5000 Frequency f Hz Figure 3 1 The SSTV frequency spectre for two various images trans ferred in Martin M1 mode 50x38 120x90 Figure 3 2 Image quality depends on resolution 3 2 Image resolution Resolution is a feature that tells what amount of details is possible to store in an image see fig 3 2 The resolution has two parameters horizontal resolution the number of image columns x number of image lines he vertical resolution In television technology the more important parameter is the vertical resolution number of lines and it is defined by the selection of the SSTV mode To get the horizontal resolution is more complicated As has been described in previous text the image is broadcast through the SSB channel on short waves and the maximal bandwidth is limited 15 3 MODERN SSTV FEATURES The SSTV is an analog mode and cannot transfer images without loss The image is not exactly the same on the reception side as on the transmission side Even if the communication channel is without any interference or noise the image is still distorted due to transmission speed and limited bandwidth The faster the transmission speed is the greater the distortion result Therefore it is very difficult to say what the horizontal resolut
64. T 24 0036 182 OAT AND TD CONTOUR T 24 1236 06Z OAT AND TD CONTOUR T 24 m 0048 122 SHIP ICE ACCRETION 1248 00Z SHIP ICE ACCRETION 0100 MAIN SCHEDULE 1300 MAIN SCHEDULE 0124 QSL REPORT 1324 QSL REPORT 0136 OCEAN FRONTS 1336 OCEAN FRONTS 01487182 300MB GPH 100 111348 062 300MB CPH Fate Hy ete Sh ae ea 0212 SYMBOLOGY 1400 002 SEA SURFACE TEMP T 12 0236 00Z SFC ANALYSIS 1436 122 SFC ANALYSIS 0300 002 SFG ANALYSIS 1500 122 SFC ANALYSIS 0348 042 GALE WARNING SUMMARY 1548 16Z GALE WARNING SUMMARY 0400 002 SFC ANALYSIS 1600 12 SFC ANALYSIS m 0412 00Z OAT AND TD CONTOUR T 24 1612 122 OAT AND TD CONTOUR T 24 0424 002 850MB WBPT PPTN T 24 1624 122 850MB WBPT PPTN T 24 ER 0436 002 SFC PROGNOSIS T 24 1636 122 SFC PROGNOSIS T 24 0448 062 SCEXAS TAFS 1648 182 SCEXAS TAFS 0500 00Z SFC ANALYSIS 1700 122 SFC ANALYSIS a 10512 002 SFC PROGNOSIS 7424 1712 122 SFC PROGNOSIS T 24 0524 00Z SFC PROGNOSIS T 48 1724 122 SFC PROGNOSIS T 48 0536 062 SCEXAS TAFS 1736 182 SCEXA TAFS 0548 06Z GALE WARNING SUMMARY 1748 18Z GALE WARNING SUMMARY 10600 002 SFC ANALYSIS 1800 12 SFC ANALYSIS 10612 002 SFC PROG T 24 1812 12 SFC PROG T 24 l m Deze DDZ JMC TIZ KSS r FREE o S Ai ae a 10636 002 JMC T 24 1836 122 JMC T 24 10648 072 SCEXA TAFS 1848 192 SCEXA TAFS 0700 07Z SPARE SCEXA TAFS 1900 192 SPARE SCEXA TAFS 0712 00Z SIG WINDS T424 912 122 SIG WINDS T4245 557 gt 0724 002 SFC PROGNOSIS T448 1924 122 SFC PROGNOSIS T
65. Table 4 4 The Martin scan line timing 4 2 4 Scottie These modes were created by Eddie T J Murphy GM3SBC He modified the orig inal firmware of Wraase SC 1 Martin Emmerson also implemented Scottie modes to Robot 1200C later on Scottie has the same improvements as the Martin system does but its scan line composition and scan timing are different After vertical synchronization the sequence of scan lines is a 1 5ms short gap of 1500 Hz then a green component a 1 5ms short gap again a blue component then a horizontal sync another gap and lastly a red component This unusual order is the result of the system adaptation to SC 1 where the additional sync was used right before the red component Syncs are permanently sent for any time synchronization during reception The Scottie relies on exact timing like the Martin although the original version for SC 1 was not fully synchronous and syncs were still processed by the converter But in newer systems the modes are implemented for free run reception so the system is equivalent to the Martin The implementation of Scottie in Robot 1200C slightly differs because the first scan line includes an additional 9 0ms sync at the beginning of the scan line right after vertical synchronization All other modes implemented in Robot 1200C have sync at the beginning of the scan line but the Scottie has the sync in the middle of the scan line which then caused color distortion Perhaps some other im
66. age processing is done in a real time digitizer and images are stored in memory with a resolution of 416x256 with 2 million colors With an optional EM 70 module the video memory capacity can be doubled Tasco TSC 70P working with PAL video signal you need to have a television with video inputs or a color TV monitor Control equipment is made via an infrared remote control WR 70 or via a RS232 serial interface Using EB 232VP software images can be moved at 115 kbit s speed between the converter and the computer The desktop PC can be equipped with an optional ISA card EB 70P that triples the speed of data exchange For greater convenience the converter can be controlled by a computer program i e HIRES 70P or WINTSC The converter weighs 450g 60g remote control with dimensions of 140mm width x 140mm length x 25mm height and it is powered by DC 11 15 V with a consumption smaller than 250 mA It is specifically designed for mobile or portable operations and can be used with miniature television such as EV 5xx from CASIO with small LCD display 7 cm it weighs about 195 g 64 SSTV EQUIPMENT 6 6 7 Interactive Visual Communicator VC H1 The VC H1 was produced by Kenwood It is a device intended for mobile SSTV operations The dimensions are similar to hand held transceivers 7x3 5x17 cm The unit has a built in CCD Camera 1 8 LCD color monitor and a microphone Its memory allows the storage of an uncompressed image in the i
67. ains 8 symbols S E L H A T R The message can be expressed with code words of 3bit length Its whole length is 3 34 102 bits For Huffman coding we need to determine number of each symbol and their prob abilities There is used binary tree it is a data structure often used in programming The symbols are sorted by their frequency and then each symbol represents a tree leaf and its weight is given by symbol occurrence In first step join two leafs with the 101 9 INTRODUCTION TO DIGITAL SLOW SCAN TV S E L H A T R 8x 7x 6x 5X 4x 2x 1x 1x 0 235 0 206 0 176 0 147 0 118 0 059 0 029 0 029 Table 9 3 none lowest weight in our case T and R and create a node The node weight is sum of weights T and R In the next step join leafs or nodes with the lowest weight and proceed as long as there is only one node the root of binary tree Now go from the root toward leafs by the edges and each edge label by 0 or 1 if the edge goes up or down in tree terminology to left or right subtree The constructed tree with labeled edges see on fig 9 2 To find the code of each symbol pass all ways from the root towards the leaves The path going along the edges of 0 0 ends in S the path going along 1 1 1 0 ends in A Symbol Code S 00 E 10 L 010 011 H 110 A 1110 T 11110 R 11111 Figure 9 2 The results of Huffman encoding
68. al which can then be transmitted over a voice channel by a communication transceiver on shortwave bands With an expansion of radio broadcast digitalization digital SSTV was also developed and uses advanced technologies like data compression error correction codes and discrete multi tone modulations for relatively fast narrow band data transfer Another option for shortwave image transmission is radiofaz the predecessor of what is now commonly known as office fax Radiofax is mostly used by meteorolog ical stations for the broadcast of synoptic maps and satellite images Or by press agencies for the broadcast of news and photographs in the past on longwave and shortwave bands Synoptic maps should be transferred in high quality so image transmission takes about 10 minutes or more on average Despite the pervasiveness of Internet technology this broadcast method is still widely used 1 PREFACE For a long time the integral part of our hamshacks has been the personal computer An essential part of a PC the sound card inputs signals into the PC And then specialized software converts the signal to data and vice versa The data that is of interest in this book will be that of transmitted images I hope this book will spur those who are interested in these fascinating modes of communication to get immediately active in the field In Zd f nad S zavou April 11 2013 Martin OK2MNM Slow scan television Slow scan television SSTV i
69. al synchro nization it is not required to detect horizontal sync Thanks to this synchronous systems are much more resistant to interference Scan line sync are still transmitted and then reception could start any time during transmission The disadvantage of free run scan is in complying to the very precise line speed of the corresponding parties The line speed must be absolutely same If the values are different there is an unpleasant effect on the picture slant For more information on this subject see section 7 3 3 6 2 Vertical synchronization VIS code Vertical synchronization is used to detect the start of transmission The receiving device can automatically begin the image scan after vertical sync 24 MODERN SSTV FEATURES 3 The Robot Research company developed a new form of vertical synchronization called Vertical Interval Signaling VIS All modern SSTV systems adopted the VIS and use these longer syncs and digital headers for automatic SSTV mode recognition The VIS contains digital code the first and last bits are the start and stop bits with 1200 Hz frequency The remaining 8 bits provide mode identification and con tain one parity bit Each bit is transmitted in order from the least significant bit 1900 Hz 1900 Hz bit 7 1 stop sync 1 image scan line 10 x 30 ms PF 300 ms Figure 3 11 Structure of VIS with value 42 Parity is used for simple error checking
70. alls should include CQ FAX TEST Report the RST and the number of connections from 001 Any QSO is a point valued multipliers are countries WAE DXCC and districts W VE and JA QSO with a same station are valid on more bands The 143 11 FACSIMILE RADIOFAX log should be sent within 2 weeks after the contest to Werner Ludwig DF5BX Post Box 1270 D 49110 Georgsmarienshuette Germany email df5bx darc de 11 6 International facsimile standard recommedation 1 Drum speed 60 90 120 240 revolutions per minute if speeds greater then 120 rpm are used they should be multiples of 60 rpm 2 Diameter of drum 152 mm in the case of flat bed scanners this will be length of the scanning line including the dead sector 3 Index of co operation IOC gt 576 for minimum black or white picture elements of 0 4 mm and 288 for minimum picture elements of 0 7 mm 4 Length of drum the length of the drum should be at least 550mm 5 Spanning density Scanning density IOC diameter of drum It is approximately 4 lines per mm for index 576 2 lines per mm for index 288 6 Direction of scanning at the transmitter the plane developed in the case of drum transmitter of the message area is scanned along lines running from left to right commencing in the left hand corner at the bottom and this is equivalent of scanning over a left hand helix 7 Dead sector 4 5 96 0 5 96 of the length of the scanning line The signal
71. ams or text must by stored in perfect form but in case of sound images or animations we can settle with the omission of certain details then we re talking about lossy compression method 9 3 1 Information entropy When Clause E Shannon was engaged in applied mathematic of communication theory during 1940s he started with definition of informational value of message content The message which is repeated often is less informative than the message which occurs sporadically So the often repeated message is more likely than the unique The probability in mathematic is expressed by real numbers in range from 0 for a completely unlikely events to 1 for the phenomena that occur surely Shan non defined the amount of information z for the message z with the probability of occurrence p z as follows I z log p z The graph of negative logarithm see on fig 9 1 if the message content is less likely that its information value is higher l p zi Figure 9 1 The relation between information con tent I z and its probability p z Information entropy H is defined as average rate of information value I x N H _plz I z pla log p z bit 100 INTRODUCTION TO DIGITAL SLOW SCAN TV 9 We show the entropy meaning in example We need to transfer messages a ao dg and probability of their occurrence is same p 1 8 0 125 The entropy of source is 8 Lt d H p a lo
72. ant amplitude in input circuits and then continues into an analog digital converter Digital data is processed by the converter s microprocessor firmware Its task is to digitize every scan line of the image and store it in memory The memory capacity is equivalent to the resolution and number of colors The memory is continuously read in the FSTV scanning frequency and data goes into a digital analog converter The output analog signal is displayed on normal television The SSTV image is stored in memory until it is overwritten by the newly received image The reverse process of digitization of an FSTV image and its transmission by SSTV is similar One of the first SSTV converters was the Robot 300 model This converter con tains 69 transistors 41 integrated circuits 41 diodes and its heart is a silicon memory tube The function of this tube was the same as a cathode ray tube or vidicon The electron beam electromagnetically diffracted and focus was directed into the scan ning electrode which consisted of a dielectric memory layer used for analog image recording 61 6 SSTV EQUIPMENT The modern concept of converters began with Robot 400C and its successors 450C and especially 1200C which became available in 1986 In these years everyone who was serious about SSTV had to own one A camera and a monitor were necessary gt RGB D A x and controller NTSC PAL encoder composite video for TV monitor RF
73. arevn p enosov soustavy BEN technick literatura 1997 Vl ek K Komprese a k dov zabezpe en v mutimedi ln ch komunikac ch BEN technick literatura 2004 Vyhl ka FMS 390 1992 Sb o povolov n amat rsk ch vys lac ch stanic Ministerstvo spoj 1992 Wolfgang Larry WR1B TASCO Electronics TSC 70U Slow Scan TV System QST Apr 1997 ra Ji Bed ich Bene Felkel Petr Modern po ta ov grafika Computer Press 1998 175
74. be transfered due to the significant bandwidth reduction During experiments it was found that an image was visible for about 8 seconds on a long persistent CRT with P7 phosphor So after reception of the last scan line the first is still visible but in a while the image slowly disappeares For the best impression it was necessary to view an SSTV monitor in a darkened room Usually several same images were transmitted in a sequence Each consequent image slowly redrew the original which was still visible on the phosphor So it was possible to display images for a longer time or to record it on a tape for later playback It was found that the ideal time for the correct detection of line synchronization pulses by electronic circuits is 5 ms and for image vertical synchronization it is 10 SLOW SCAN TELEVISION 2 30 ms Vertical synchronization initiates the automatic start up of the image display on the CRT The synchronization frequency for scan lines and frames was derived from the electric mains frequency For horizontal scan 50 Hz divided by three 16 6 Hz is used And for vertical scan 1 7 2s 0 1388 Hz is used this is the mains frequency divided by 360 3x number of lines 120 The parameters are derived in the same way for countries with 60 Hz mains The video signal band was chosen in the range from 1500 Hz for black up to 2300 Hz for white Sync pulses have a frequency of 1200 Hz and because they are blacker than b
75. bers of the Moscow SSTV is valuated by 3 points and one point for contacts with CIS countries or stations not members of the Moscow SSTV 1 Send GCR list and fee of 5 10 IRC or equivalent to Verigin Dmitriy Andree vich Lyubertsy Moscovskaya oblast Novaya street 10 48 140002 Russia email ragahq online ru http olympia fortunecity com bruno 544 award msstvs rusaward html 8 4 Contests Contest Date DARC SSTV Contest 3 d weekend in March 9nd Russian SSTV Contest Saturday in April NVCG SSTV Contest 2d week of July Danish SSTV Contest 15t weekend in May DARC HF FAX Contest 3 d weekend in August JASTA SSTV Activity from 1 to 315 August Ukrainian SSTV Contest 1 Saturday in December Table 8 3 none 8 4 1 DARC SSTV Contest It takes place the 3 d weekend in March begins at 12 00 UTC on Saturday and ends at 12 00 UTC on Sunday Competing has categories operator and SWL on the bands 3 5 to 28 MHz Transmit RSV and the number of QSOs beginning with 001 each QSO is valued by a point Multipliers are WAE DXCC countries W VE and JA districts Logs should be sent within 4 weeks after the contest at Werner Ludwig DF5BX Post Box 1270 D 49110 Georgsmarienshuette Germany email df5bx darc de 8 4 2 Russian SSTV Contest Takes place in 22d Saturday in April from 00 00 MSK to 24 00 MSK UTC MSK 3 Bands 80 40 20 15 10 6 2m There are several categories
76. ble 4 1 Parameters of black and white SSTV modes The advantage of longer transmission is improved image quality The disadvan tage is that a lot of time is needed for the transfer which could be better utilized for the transmission of color images 4 2 Color SSTV modes You might find it incredible that the first color transfer was made before the era of digital converters using long persistence monitors Each color image channel was obtained using color filters which were subsequently held in front of the camera A sample result could be that the first channel transferred was blue then green and the last red Slightly more difficult was the processing on the receiver side This was because each color channel had to be photographed from the monitor screen and then the resultant color picture was combined from all three components It was a very laborious process but it was put into practice a few times Further experiments with color SSTV transmission were based on frame sequential transfer Three complete images were transferred in 8s mode and each contained one color channel together they formed one color image During broadcast a color 30 FORMATS OF SLOW SCAN TV TRANSMISSION 4 OR L f jj EUSlow Scan Robot B amp W 24 Robot B amp W 36 Figure 4 1 Comparison of Robot system s BW modes z original was progressively scanned with a BW camera through each of the color filters Received images had to be stored in a di
77. by these three parameters gt Amount indicates how much will increase the contrast of edges by the edge lightens or darkens this setting will affect most the degree of sharpening gt Radius sets how much pixels around edges will be used For smaller radius the filter affect also smaller details but for greater it may produce a bright rim around edges gt Threshold controls the minimum brightness change that will be sharpened Thanks to threshold it is possible to enhance only stronger edges and finer leave un changed 171 13 COMPUTER IMAGE PROCESSING Original image Sharpening Hy from CCD camera Sharpening Hg radius 2 5 amount 1 5 threshold 0 Figure 13 10 Results of image sharpening No wonder that unsharp mask is considered as king in improving the image The only drawback is that if you blow over it then around edges occurs distinctive bright rim and the image looks unnaturally 172 OMPUTER IMAGE PROCESSING 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 References Ad mek J K dov n SNTL 1989 Abrams Clay K6AEP Taggart Ralph WB8DQT Color Computer SSTV 73 Nov Dec 1984 American Radio Relay League The ARRL Handbook for Radio Communications ARRL 2011 Barber James L N7CXI Proposal for SSTV Mode Specifications Dayton SSTV forum 2000 Bodson Dennis W4P WEF Karty Steven N5SK FAX480 and SSTV Interfa
78. can rates but in the number of lines transferred in one minute lines per minute lpm Line speed depends on the selected mode and varies in the range from 571pm Scottie DX for high quality transmission of colour image 320x240 in nearly five minutes up to 1000 lpm for BW image 128x128 in just 8 seconds SSTV modes and their properties are described below 3 4 Black amp white transmission For a black and white BW monochromatic image broadcast only one signal is needed It represents brightness luminance Y of each image element 16 MODERN SSTV FEATURES Test pattern original Martin M2 220 us Robot 36 Color 280 us Martin M1 450 us MP115 680 js 3 MODERN SSTV FEATURES gt www 2 Martin M2 Figure 3 4 The comparison of two modes in real conditions of 14 MHz band The frequency ranges from 1 500 Hz black to 2 300 Hz white transmit image information Each frequency in this range represents specific brightness the level of gray Human vision can distinguish brightness in a wide range but can only adapt to the geometric mean value of actual brightness Around this value about 100 to 110 gray scale levels can be differentiated Based on this fact an ideal transmission could be regarded as 128 gray levels At this figure the average observer would not normally see transitions between adjacent grades If we want to transmit images in 128 gray levels this is the distance of s
79. can only compare the signal with anothers in current conditions on a band Video the quality of received image you can consider visually in 5 de grees see fig 8 2 The same method is used in ATV picture qual ity reporting system R Readability S Sig strength V Video 1 Unreadable Faint signal barely perceptible Barely perceptible 2 Barely readable occasional words Very weak Poor distinguishable 3 Readable with considerable Weak Fair difficulty 4 Readable with practically no Fair Good difficulty 5 Perfectly readable Fairly good Excellent 6 Good 7 Moderately strong 8 Strong 9 Very strong signals Table 8 2 Signal reporting with RSV code The report can expand information on interference QRM QRN or if the image is slanted add entry SLANT The example report is RSV 595 when the reception is awesome 82 HAM RADIO IMAGE OPERATIONS 8 Excellent Figure 8 2 Picture quality reporting system 8 2 SSTV not only for hams The SSTV found application in other sectors in the past mainly due to commercial production equipment destined for amateurs and image transfer by phone Perhaps the most notable applications is the use of SSTV to monitor active Vol cano 20 U S Geological Survey installed in September 1987 sensing camera and FM radio transceiver for observation of volcanic activity on Mount St Helena SSTV was used for remote medical ap
80. ces and Software QST Jul 1998 Bruchanov Martin OK2MNM Jest k SSTV AMA magazin Gervenec 1997 Cameroni Giuseppe I2CAB Morellato Giancarla I2AED Get on SSTV with the C 64 Ham radio Oct 1986 Churchfield Terry K3HKR Amiga AVT System 73 Amateur Radio Jul 1989 Cordesses Lionel Cordesses Roland F2DC Some Thoughts on Real Time SSTV Process ing QEX No 218 May June 2003 Cook S A G G5XB Hellscheiber What is it and how it works Radio Communication Apr 1981 Dewitt H William W2DD The Robot Research Inc Model 1200C Color Slow Scan Con verter CQ Jun 1988 ETSI Standard Digital Radio Mondiale DRM System Specification 2005 ETSI ES 201 980 V2 2 1 Dobe Josef Zalud V clav Modern radiotechnika BEN technick literatura 2006 Evers Hans PAOCX The Hellscheiber Rediscovery Ham Radio Dec 1979 Fanti Franco Facsimile CQ TV vol 88 1974 Fingerhut K P a V Amat rsk televize Svazarm 1983 Frejlach Karel Prem sign lu SSTV mikropocitacem ZX Spectrum Radioamat rsky zpravodaj vol 4 9 1989 Frejlach Karel Digit lni radioamat rsky provoz Autor vlastn m n kladem 1998 Ford Steve WBSIMY TV on 10 QST Apr 2001 Furukawa Bruce T Murray Thomas L McGee Kenneth A Video Surveillance of Active Volcanoes Using Slow Scan Television USGS Bulletin 1992 Geier Michael Jay KB1UM The SSTV Explorer Radio Fun vol 6 1995a Geier Michael Jay KB1UM
81. d be about 8 10 dB The selection of modulation depends on an user and an actual conditions prevailing on the band Other HamDRM features that can be set by user are following gt Interleaving is used for change of symbol sequence it is a way to arrange data in a non contiguous way to increase performance The long interleave has 2 seconds it supports better error correction but causes longer delay during decoding The short interleave take 400 ms Bandwidth can be changed to 2 3 kHz or 2 5 kHz A narrower SSB filter can be used for lower bandwidth but transfer speed is little lower Amount of instances is value that gives number of file repetitions during trans mission If there is more than one instance then all segments will be repeated and 118 DSSTV TRANSMISSION SYSTEMS 10 the error parts can be corrected automatically on reception side during second or third instance The number of instances makes transmission time longer gt Leadin is broadcast at beginning of transmission This initialization is used to receiver synchronization extra time allows better synchronization and automatic set up of reception settings Details of the mode and its parameters along with the call sign is broadcast throughout the transmission with QAM 4 modulation so it is possible to tune to signal during transmission but the complete data will be received if at least one complete instance of the transferred file is received
82. d lead to the loss of a few lines or the whole image The differences between modern SSTV modes and this old system are many but one parameter remains the same Almost all new systems use 1200 Hz frequency for sync pulses and the frequency band from 1500 Hz black to 2300 Hz white for video signals Also the old 8s mode is still supported by many SSTV programs for transmission It is important to note that 8s mode has the shortest transfer time and should be used in special conditions 4 1 1 Modes for digital converters There are many modes for B amp W image transmission which differ in transfer time and resolution Modes Wraase and Robot are implemented in modern converters The transfer was extended to 256 lines and also transmission time was prolonged to achieve better horizontal resolution Commonly used modes were the 16 second mode with 128 lines 32 second mode with 256 lines and the 64 second mode with 256 lines which provides maximal image 28 FORMATS OF SLOW SCAN TV TRANSMISSION 4 quality All these modes are related to the original 8s mode and also have image aspect ratio 1 1 The number of lines columns or both were simply multiplied twice This design was used in Wraase B amp W converters While Wraase modes were derived from the European 7 2s mode the Robot Re search developed an original system for their converters Robot modes aren t simply derived by doubling parameters but their parameters are derived from li
83. dcast service attributes during multiplexing 10 2 1 Comparison of HamDRM and RDFT There are several software products for RDFT and HamDRM but preference of users inclines to HamDRM Main reason for HamDRM popularity over RDFT are 120 DSSTV TRANSMISSION SYSTEMS 10 f 51 subcarrier signal bandwidth 1 subcarrier p TT TOfTT OT TT OT DUM TEN eee M eee ee ee aa w wow ww lt 1 ow oou lt a ZINC aa lt o3 3 lt ZI Noo lt 1 w a s a NM ui ZI No ooo wa Oo 20 X 0 f 0 X f0 0 X 0 g 2 11 0 X Of 0 Xf O0 0 gt c aa awa USA a U aaa di DEA aa wala aa sa bes a B NEROMECOLPAIMEOIER CIEN CR MEE EEEE E V 0 f 0 X 0 0fX 0 f 0 X 0 o naa ox we MEO a a a a a a a a Ma a u a l Ua IN n a a Ul ou a a i a a a a u u u oc on n n mn a YaNa n a M oaa a d n te AN a d M a a a a M oa AN a a M oa u on u u uo cO X cogis 0 Xf 0 f0 X 0 d Y 0 EC ARN DN OfX 0 f 0 X 0 g freq pilots for manual tunning Figure 10 9 Example of frame for Mode B spectrum occupancy 2 5 kHz Leg end DC carrier MCS cells X FAC cells T time pilots f frequency pilots O scattered pilots boosted scattered pilots it is possible to decode and display image during transmission transfer speed is better up to 3x HamDRM continuously broadcasts station identification so receiving operat
84. detection and correction S RA Cyclic redundancy check 0 2 2 Hamming code 9 2 3 Reed Solomon code 9 3 Data compression Bad Information entropy 93 2 Huffman coding 9 3 3 Lossless data compression 9 3 3 1 Portable Network Graphics 9 3 4 Lossy compression 9 3 4 1 JPEG compression 9 3 4 2 JPEG2000 9 3 4 3 Lossy versus lossless image compression conclusion 79 82 83 84 84 84 84 85 85 85 86 86 86 8T 8T 8T 87 90 9t 92 94 95 96 98 98 99 99 100 101 103 103 104 104 107 109 10 DSSTV transmission systems 10 1 Redundant Data File Transfer 10 1 1 RDFT operations 10 2 HamDRM system 10 21 Comparison of HamDRM and RDFT 10 2 2 Quadrature amplitude modulation QAM 10 2 3 Orthogonal frequency division multiplexing OFDM 10 2 3 1 OFDM transfer 10 38 DSSTV software selection 10 4 Making QSO 10 5 Waterfall images 11 Facsimile Radiofax 11 1 The history of image transmission 11 2 The fax mode 11 2 Image transmission 11 2 2 The reception 11 2 2 1 Facsimile transmission modes 11 3 Professional stations 11 4 Satellite imagery retransmission 11 4 1 Meteorologic satellites 11 4 2 Essential Services 11 5 Hamradio facsimile operations 11 5 1 EU FAX Diplom 11 5 2 The International HF FAX Contest by DARC 11 6 International facsimile standard recommedation 12 List of professional stations 12 1 Europe 12 1 1 Athens Greece 12 1 2 Hamburg Pinnenberg Germany 12 1 3 R
85. e analog WEFAX broadcast in 1 6GHz band was discontinued For analog WEFAX reception could be used NOAA receiver with band converter and dish or yagi antenna The follower of the analog broadcasst is new system MSG Meteosat Second Genereation it is fully operational since 2004 Digital data LRIT Low Rate Information Transmission and HRIT High Rate Information Transmission are broadcast via television transponder EuroBird9 Ku band 10 7 12 75 GHz on 11 976 82MHz EUMETCAST An extension PCI card for DVB S reception is used for data reception e g SkyStar2 card for PCT or external version for USB The data are decoded with tq TELLICAST software The disadvantage is that almost all data is distributed encrypted so it is necessary to register at Eumet sat provider and buy the hardware decoding key The price for hobby purposes is 100 software is for 60 and key is for 40 The are also higher demands on PC configuration 2GHz CPU 1 GB RAM and 36 GB hard disk The radiometer of Meteosat 8 and 9 provides images in 11 spectral channels in 3 km pixel resolution and in HRV High Resolution Visible channel it is 1 km pixel although in regard to slant projection of the Earth s surface the resolution for Europe 141 11 FACSIMILE RADIOFAX and Globe edges is lower Image data High Rate SEVIRI have a standard size 3712x3712 pixels and for HRV it is 5568x11136 pixels Data from satellite are send first to the primary station
86. e direct FFT to obtain individual subcarriers Two data stream are outputs of FFT which are converted with digital analog converters on two analog signals Then these signals are modulated to main carrier and there is a phase of 90 between them The Re signal presents amplitude com ponent and Im signal phase component Both joined together creates transmitted OFDM signal Everything on reception side goes in opposite way The received signal is amplified and converted to lower frequency Then signals Re and Im go through low pass filters to analog digital converters and data from them is processed by DSP with direct FFT and divided into individual subcarriers The output data are compiled in parallel serial converter 125 constellation mapping 10 DSSTV TRANSMISSION SYSTEMS serial parallel D A convertor convertor E Inverse Discrete pager data Fourier Transformation frequency FFT D A convertor Figure 10 14 The OFDM modulator use fast Fourier transform FFT for making a huge number of modulated subcarriers OFDM signal 10 3 DSSTV software selection There is several programs available supporting HamDRM and RDFT Software RDFT HamDRM Web page DIGTRX 3 11 http www qslnet de member py4zbz hdsstv HamDRM htm DigiACE V1 9 http homepage ntlworld com mhemmerson DigPAL http www home bellsouth net p PWP hampal EasyPAL http vk4aes com HamPAL http www home bellsou
87. e less resistant to interference than their RGB counterparts see fig 3 10 The RGB model is distorted by a low contrast or increased brightness when there is significant deviation 200 Hz from the transmitter carrier and thus provides better colours than Y CrCb Selective fading is a phenomenon where the signal comes from two paths in which one signal path is the variable and causes instability of the ionosphere layers It can be often seen in the 80m band in the morning and evening 23 3 MODERN SSTV FEATURES Figure 3 10 Color distortion of RGB when the station is improperly tuned 3 6 Synchronization 3 6 1 Horizontal synchronization There are two types of synchronization synchronous and asynchronous Older SSTV systems use asynchronous transmission This means that each in formation frame in our case a scan line will be received after the detection of horizontal sync This system detects vertical image and horizontal scan line syncs and only after proper detection will it display the received lines Asynchronous transmission has a huge disadvantage When interference happens close to the 1200 Hz frequency an SSTV device can lose several scan lines if interference remains In this respect all new SSTV systems are improved and use synchronous trans mission These systems use free run scan It is not necessary to receive vertical sync and it is possible to begin reception from any scan line After initi
88. e malicious sounds that could accidentally key the transmitter 3 Automatic PT T switch can control a computer All SSTV programs support PTT control over a simple serial port COM RS 232 circuit The circuit contains one switching transistor or opto isolator and few passive parts See schematic 7 8 for details The control signal is connected to RTS pin 7 at Cannon DB9 connector 4 at DB25 or DTR 4 at DB9 20 at DB25 selected pin can be changed by software configuration The ground is on serial port wired on pin 5 at DB9 or 7 at DB25 The big amount of handheld TRXs has a similar pin for microphone input and PTT In this case an audio signal should be galvanicaly separated by capacitor about 100nF and PTT signal is connected by resistor which resistance can by find in TRX instruction or you can connect trimming resistor about 15 kQ and test the max value when TRX switching 4 Some transceivers support control over serial port This CAT Computer Aided Transceiver interface can provide PTT switching Over CAT interface can be send commands e g for tuning mode control etc This method must be sup ported by software for example MixW can control some TRXes so it is not needed to practically touch the TRX buttons What to do if your computer is not equipped with serial port Some mother board manufacturers build only one serial port and notebook manufacturers doesn t provide any serial port If this happens you can use VOX or obtain USB
89. e of most important tools in professional graphics editors It provides the complex settings of color tone brightness and contrast The GIMP tool Adjust Color Curves pic 13 4 is in menu Colors Curves Its functionality is very similar across image editing software The work with curves is quite simple The tool window has on the x axis displayed input luminance values and on the y axis output values which are presented as gray scale The curve self is the function y f x and it transforms input values to output and by its shaping the user sets the parameters of the transformation At the beginning the transformation function is y x and therefore the output level is equal to input When you touch the curve by cursor a control point appears on the curve You can move this point in every direction and if the option Preview is switched on then the results will be shown immediately It is possible to add more control points for continuous transformation or you can set any curve shape with discontinuous transformation What you can do with it The results of transformations and the used curves is in pic 13 5 You can spread input values by histogram and improve contrast 13 54 Another use is to darken or lighten the image but there is many more options how to do this then a simple setting of levels With the curve you can focus on a range of colors can edit only midrange portion of color scale and keep black and light pixels if you ho
90. e optimal radius for given image location automatically the user parameters are ignored 13 3 3 Sharpening Often happens that images from cameras or scanners have reduced sharp edges In this case you can try to use sharpening filters for edges highlighting There are two convolution kernels for sharpening H4 and Hg with an even stronger effect 0 0 1 1 1 0 1 U 1 1 1 In the GIMP the sharpening filters are in the menu Filters Enhance The first one is Sharpen and it has similar results as kernels above and it is possible to set sharpening level and from preview select the best results The disadvantage of these filters is that it also highlights the image noise and some other unwanted details It can be seen in fig 13 10 when the filter Hj is used so there appears teeth on vertical edges caused by camera interlacing In this case it s possible to use filter called unsharp mask The unsharp mask procedure in first step apply Gaussian blur on image copy and then check the difference between blurred and original image When the difference is greater then a user defined threshold then both images are subtracted and the result is added to original image The threshold limits the sharpness of output image so small details of certain size is not sharpened Thanks to this the sharpening does not apply to noise and graininess The digital unsharp mask is great filter for enhancing sharpness Some results are influenced
91. e remaining two modes SC 2 30 with 128 and SC 2 60 with 256 lines have about half of the resolution found in SC 2 120 Mode Transfer Color Scan line ms Speed Resolution name time sequence Sync R G B lpm Wraase SC 2 30 30 256x128 R G B 5 0 58 0 117 0 58 0 249 600 Wraase SC 2 60 60 256x256 R G B 5 0 58 0 117 0 58 0 249 600 Wraase SC 2 120 120 320x256 R G B 5 0 117 0 235 0 117 0 126 175 Wraase SC 2 180 180 512x256 R G B 5 0 235 0 235 0 235 0 84 383 Table 4 7 Wraase SC 2 scan line timing 43 4 FORMATS OF SLOW SCAN TV TRANSMISSION 4 3 High resolution transmission High quality images consume a lot of memory but memory was very expensive in early computer systems High resolution images were a real luxury but over the years memory has gotten cheaper therefore modern SSTV systems now have modes for high resolution broadcast too 4 3 1 FAX480 Synchronous mode was the first high resolution mode It was first implemented in the ViewPort VGA interface and software for IBM PCs in 1993 The old VGA cards with 256 kB of memory can hold an image with a resolution 640x480 with only 16 colors This provides only gray scale images so this mode is used for only B amp W transmission The image resolution of FAX480 is 512x480 and the transmission time is 138 seconds In the early days of high resolution transmission the only way to trans mi
92. ean amateurs widely used the SSTV mode called Martin M1 but in recent times other modes Martin M2 and Scottie S2 are also in use A special mode used Scottie DX is characterized by very high image quality And the mode Robot 36 Color is undertaken in space communication Fortunately all modern converters and computer software are able to operate with these popular modes so the problem that two stations can not establish the QSO should not occur A digital vertical synchronization for automatic mode selection will be described shortly because every mode uses a digital header for its identification Thanks to this any SSTV device can automatically switch to the correct mode and begin re ception Computer software also supports mode detection by measuring the elapsed time between two successive sync impulses of image lines More details will be described in the following chapters 3 1 Signal modulation 3 1 1 Bandwidth Different communication channels whether wired or wireless have several charac teristics which define their behaviour in the transfer of effective signals These include for example attenuation Attenuation defines how much the communication channel reduces a transferred signal Another important characteristic is the bias which refers to the various distortions that occurs due to imperfections within the communication path There are several negative influences that affect signal transfer within a commu nication path
93. ed in reception of satellite imagery there is few basic informations For amateur reception it is possible to use NOAA satellites on low Earth orbit These satellites transmit in 137MHz band in WEFAX mode with amplitude modu lation so an sound card can be used as signal decoder with some dedicated software like JVComm32 or WXtoIMG For the best reception should be used a receiver with 30 kHz intermediate frequency IF width which unfortunately common receivers and TRXes don t support The narrower IF causes image distortion and receiver for wideband FM about 200 kHz is not very suitable due to more noise that affecting signal Also it is necessary to use an antenna with right handed circular polarization as turnstile antenna crossed dipoles or QFH Quadrifillar Helix Antenna Satellites NOAA MetOp and Fengyun are carrying high resolution scanners and digital transmitters HRPT High Resolution Image Transmission They broad cast on 1 6GHz band but used system is digital and for data reception must be used band converter special modem and main difficulty rests in need of antenna aiming A computer controlled rotator is needed for aiming of azimuth and elevation 140 FACSIMILE RADIOFAX 11 Figure 11 10 Restransmission of satellite image from Boston NMF station re ceived on 12 750 kHz hurricane Katrina is devastating Mexican gulf Next option is a reception of geostationary satellites of Meteosat and GOES fam ily Th
94. erall quality It means that each pixel takes a long time and this gives better noise and phase distortion immunity But these qualities are compensated by a very long image transmission time of about 4 5 minutes During this time two images with the same resolution can be sent with other RGB modes The Scottie DX mode offers high quality images but sometimes the optimal conditions for DX connections do not last long enough for the transfer of a whole picture Mode Transfer Color Scan line ms Speed Resolution name time sequence Sync G B R Ipm Scottie S1 110s 320x256 G B R 9 0 138 240 138 240 138 240 140 1148942 Scottie 52 71s 160x256 G B R 9 0 88 064 88 064 88 064 216 0667214 Scottie 53 55 8 320x128 G B R 9 0 138 240 138 240 138 240 140 1148942 Scottie S4 36 s 160x128 G B R 9 0 88 064 88 064 88 064 216 0667214 Scottie DX 269s 320x256 G B R 9 0 345 600 345 600 345 600 57 12653528 Table 4 5 The Scottie scan line timing 4 2 5 Amiga Video Transceiver AV T modes were originally intended for SSTV operations with Amiga computers AV T author Ben B Williams AA7AS developed a dedicated interface and software 39 4 FORMATS OF SLOW SCAN TV TRANSMISSION which was produced by AEA Advanced Electronic Applications Inc Although the creator claimed that this system was a revolution in SSTV transmission these m
95. erators use IOC 576 or 288 and speed 120 lpm or 240 lpm the usage of other modes depends on agreement of both parties A report is given in common RST code Readibility Strenght Tone An opportunity to receive rare facsimile amateur stations is weekend in Au gust when The International HF FAX Contest by DARC is active Those who are interested in this kind of communication mode may also try to obtain a diploma awarded by the DARC for two way contacts 3rd 142 FACSIMILE RADIOFAX 11 Figure 11 11 Hamradio facsimile from ON7BW received on 14MHz band speed 240 lpm IOC 288 11 5 1 EU FAX Diplom The diplom is award for two way facsimile contacts with European countries There are three degrees for QSO with 10 prefixes in 5 countries 20 prefixes in 10 countries and 40 prefixes in 20 countries European countries are given by WAE list Valid QSOs are from 1 1 1980 and QSL cards must have note 2 WAY FAX A confirmed list of QSL cards and 5 send to DARC FAX Manager Werner Ludwig DF5BX Post Box 1270 D 49110 Georgmarienshutte Germany 11 5 2 The International HF FAX Contest by DARC The contest is organized by the Deutscher Amateur Radio Club Ongoing 3 week end of the August starts at 8 00 UTC on Saturday and ends on Sunday at 20 00 UTC It progress on all HF bands except the WARC Assessed by two classes listeners and one operator All QSOs must be done in facsimile mode and image c
96. erter indicates the accuracy of signal 68 COMPUTER OPERATIONS 7 t Figure 7 3 The frequency spectrum of signal in fig 7 2a Figure 7 4 The signal sampled with a frequency higher than 2f mar amplitude scan in a defined range for 8 bits it is 28 256 values and for 16 it is 65 536 Constrained resolution of A D converter causes an quantization error E g for 8 bit converter processing voltage range 0 5 0 V it s the error 5 0 28 1 0 02 V The 8bit converter cannon distinguish voltage levels lower then 0 02 V So for input voltage 3 111 V it could find corresponding numeric value 100111105 3 098 V or 100111115 z 3 118 V because less significant bit is influenced by quantization error The size of the error can be decreased by greater resolution of A D converter For our purposes the 16bit resolution is acceptable A modern sound cards could be equipped with digital signal processor DSP which extend card functions e g for filtering or data compression during recording 69 7 COMPUTER OPERATIONS Figure 7 5 The sample rate does not meet the Shannon s theorem so it can lighten load of main computer CPU E g Sound Blaster Live contains programmable DSP labeled EMU10K 1 The choice of sound card type depends only on user s preferences and his intends of use Many PCs has integrated sound card directly on a motherboard 7 2 3 Interface between TRX and PC The basic interface is made of s
97. et supply noise audio level etc The TX offset issue is often pretty messy You can notice that some software running concurrent with your SSTV program can influence sound cart output and then the change of sample rate occurs Even the simple Volume Control tool can do this So it is useful to stop unnecessary program running in the background Especially programs that can influence sound card output or decreases stability of Microsoft Windows You may notice a strange behaviour if you are user of modern sound card with full duplex mode enabled with several output channels with a support of different sample rates for each channel This is for example SB Live Value I have noticed that my TX offset randomly changes I have this experiences with SB Live Value and I found that another radio amateurs has same You can try to set other sample rate than 11 025 0 Hz in this case if this doesn t load your computer too much For example try 48 000 0 Hz this value is fixed sample rate see your card user s guide and best results you can achieve with using of this value or its half or quarter 24 000 0 kHz or 12 000 0kHz When you change this value you need to recalibrate your accurate timing again To avoid these problems you can constantly monitor the outgoing signal through the external feedback with the TRX monitor enabled and before your today first transmission you will check that everything is fine It s unpleasant that problems often occur
98. etimes there should arise a moir here on the raster of changing white and black stripes Almost every image editing software give an option for used scaling method so choose linear interpolation or bilinear or bicubic A raster image for interpolation must have at least 16bit color depth on indexed images with 256 or less colors it doesn t work but you can convert them to more colors temporary and then back 13 2 Color adjustment Basic tools for the color adjustment can edit image contrast brightness color sat uration and hue The advanced tools are curves adjustment and image histogram The histogram is a representation of the distributions of colors in an image see pic 13 2 It is bar graph and there is representation of the tonal variations on the horizontal axis and the vertical axis represents the number of pixel in the particular tone In digital photography you can easily review exposure by histogram If the image is underexposed the amount of darker pixels lays on left side of graph more darker pixels vice versa for overexposed images there is high number of lighter pixels on right side It is possible to check exposure in the digital camera menu and take snapshot again of course unless the image wasn t dark or light in principle The ideal case is if the luminance is wide spread inside the luminance range For low contrast the luminance values are spread only over smaller range of luminace The histogram equalization can
99. g p z s z g 1083 3 bits 1 The observed entropy determines how the message content can be encoded for data transmission The length of message in bits is greater then or equal to the entropy without loss of information So the message can be encoded as word of 3bit length 000 001 010 Maximum entropy is reached when the probability of occurrence of each message is the same But the messages have often different probabilities in many cases In this example we need to transfer messages a 45 a07 Their probabilities are p a 0 235 p az 0 206 p a4 0 176 p a4 0 147 play 0 118 plag 0 059 p a7 0 029 p ag 0 029 Entropy of source is H Yo log p a 03235 2 09 0 206 2 28 0 176 2 50 0 147 2 76 0 118 3 08 0 059 4 08 0 029 5 08 0 029 5 08 bits H m 2 712 bits We see that the entropy of source is lower and because data bits are not divisible it is necessary to encode the message again to the words of length 3 But suspect that such an encoding is no longer optimal There is the idea to encode frequently occurring words as the message of the shorter length This idea was well counseled by David A Huffman the Shannon s student 9 3 2 Huffman coding We can show an example of Huffman coding construction The message we are going to encode if following THE SHELLS SHE SELLS ARE SEASHELLS This message cont
100. ght corner are just zeros This matrix is linearized into a sequence Thanks to zig zag reading the non zero values appear in front of the sequence and remain part is filled by unnecessary zeroes Then the sequence is divided into categories the first is DC coefficient and then other values continue and for each is determined following values number of pre ceding zeros category intrinsic value The redundant zeros are reduces by RLE coding and from some place are presented only zeros The all zeros are omitted and replaced by EOB end of block mark DC coefficient brightness and chrominance values have their codings For AC coefficients are zeroes labeled as category 0 for other integer values their categories is given by bit length of value For most common AC coefficients 1 1 it is 1 these two values can be represented by value 0 or 1 for 3 2 2 3 is length 2 and it is represented by 00 01 10 11 for 7 4 4 7 is length 3 etc The result code depends on number of preceding zeros and bit length so 0 1 no zero length 1 has 00 0 2 01 0 3 100 1 1 1 zero length 1 1100 5 1 1111010 etc The results of Huffman coding for one block se in fig 9 3 We have an option to choose the image quality for JPEG files For quality of 75 96 the distortion is not noticeable in most cases and compress ratio can be around 20 1 to 25 1 The results of different quality for image with 256 x 192 seen in
101. gital converter in three different memories When simultaneously displayed on a color monitor they created a full color image This is the reason why BW modes of Robot and Wraase families have three different VIS codes for BW transfer The codes are sent for adjustment of color components for frame sequential transmission Individual images were usually sent in the order of red green blue But the order of the channels could be changed under the agreement of corresponding stations or some images could be broadcast repeatedly With such a method it is possible to transfer only static scenes If an object moves during manual scanning of an image the color components do not correspond and the result image has colored ghosts The transfer was not always reliable due to interference and fade outs the im age component had to be sent several times And in practice it was sometimes problematic to complete all color channels To improve color transmission the line sequential transfer was developed The principle is that it transmits a single image 31 4 FORMATS OF SLOW SCAN TV TRANSMISSION and each scan line carries all three color components A receiving equipment can al ready display color images during transmission This method where the color image is transferred in one frame is referred to as SFC Single Frame color More properties of SSTV systems will be introduced in following sections with all their pros and cons and detail
102. gital data Contrary to popular SSTV operations when stations restrict only to the exchange of images the phone mode is much more used in case of DSSTV The choice of images is not limited to the usual 320 x 240 resolution but there can be used any resolution The limiting factor is only time of transmission e g in the DIGTRX software the broadcast time is already known so you can play around with the compression level resolution or number of colors and achieve a reasonable compromise Also the transmitted data file format can be any Listen on the band and you will make sure that JPEG2000 is often used but also animated GIFs or text files with ASCII art 10 5 Waterfall images For digital SSTV and RDFT or HamDRM system is used tuning indicator which displays spectrum of SSB channel The image showed by indicator is created using discrete Fourier transformation The indicator displays new samples on top and the old samples disappear at the bottom and the whole spectrogram is moving down so the indicator was nicknamed waterfall In the fig 10 6 and fig 10 8 you can see station and software identification and also messages about reception confirmation request for repeat or more complex pictures also The principle of waterfall images is based on Fourier transformation and the fact that the signal can be compiled from a huge number of harmonic waves If the proper harmonic are compiled so the resulting carrier wave has frequency
103. h conventional equipment without inter lacing support because their line speed are the same as for Wraase SC 180 TV 1 and Martin M1 TV 2 modes But in this condition the image will contain four bars with all quarter frames Figure 4 8 MSCAN TV image interlacing 4 4 2 Kenwood FAST FM This mode is built in the mobile SSTV converter Visual Comunicator VC H1 from Kenwood see section 6 7 This unit support some normal modes and the FAST FM mode 47 4 FORMATS OF SLOW SCAN TV TRANSMISSION The FAST FM mode sends video signals in the 2800 Hz black to 4400 Hz white band The vertical synchronization and VIS code format is similar to Robot s stan dard it has a value of 90 but uses odd parity the number of logical ones must be odd After the VIS code there is a digital header and then an image with a resolution of 320x240 The duration of one scan line is 53 6ms so the total transmission time for an image is 13 5 seconds The mode uses YCrCb color coding in the 4 2 0 format The brightness signal occupies 35 4ms of scan line and than there is a pulse of 3600 Hz that lasts 0 41 ms and then color signals are sent Each even scan line contains R Y and odd line R Y The scan line is ended by 0 41 ms pulse again The transmission of a whole image is ended by one second pulse of 1900 Hz Due to fast transmission the used bandwidth of FAST FM is in 1 0 to 6 2 kHz range so it cannot be used in the SSB voice channel
104. he CQ picture should contain text CQ UKR Contest Exchange report RSV and number from 001 Ukrainian stations send two letter region code too The score is 1 point for QSO with same country station 2 points for same continent QSO 3 points for QSO with other continent QSO with Ukrainian station is for 10 points Multipliers are DXCC and WAE countries and Ukrainian district for each band The score is counted separately for Ukrainian and foreign stations Logs send in usual form for each band to organizer UKR SSTV CONTEST P O Box 10 Kerch 98300 Ukraine 8 5 SSTV repeaters An SSTV repeater is radio station for relaying of SSTV signals A typical repeater is equipped with HF or VHF transceiver and computer with sound card A software must have an option to work as repeater SSTV repeaters are used by amateur radio operators for exchanging pictures If two stations can not copy each other they can still communicate through a repeater To activate repeater send the activation tone of frequency 1750 Hz when the repeater is activated it s send K in morse code The station must start send ing a picture in approximately 10 seconds After reception the received image is transmitted on the repeater s operation frequency Repeaters should operate in common SSTV modes but it depends on the software used MMSSTV JVComm32 MSCAN Some repeater are not activated by audio tone but instead by the SSTV vertical synchronization signal Some
105. he errors during transmission cause replacement of one symbol to another and Hamming distance indicates how many replacements may occur to change the codeword to another valid codeword Is is advantageous to have a Hamming distance of codewords larger as possible So if you want code that reveals just one error bit the minimum distance must be d 2 Block code with minimal distance d detects all t multiple errors for t lt d If there is too much errors that t dort gt d there should be created a new valid word so the error cannot be detected The code can correct errors for larger d if for error word is found a valid codeword with smaller Hamming distance between error and valid word The block code corrects all t multiple error when A d lt 3 These findings can be demonstrated on a simple case of 2 bit code secured with even parity Two bit code can have a total of 4 words of information and a redundant bit will be added so that the number of log ones in the codeword will be even The resulting code words have 3 bits and there are 2 8 different bit words code words are bold The minimum distance d of our parity code is equal to 2 so the code is able to detect just one error When word 011 is sent and 010 is received we know that there is an error If there are two errors and 011 changes to 000 then there is a word that belongs to a set of codewords and error isn t detected In the following sections are described some commonly u
106. hielded cables and 3 5mm jack plugs A reception cable connects sound card input Line In and TRX headphones output or output for external speaker For use of sound card microphone input can be used TRX output often labeled as AF OUT with impedance about 10kQ which gives max output voltage 100mV This output could be also used for interfacing tape deck or audio amplifier Microphone input of sound card has automatic gain controller AGC for better recording and it is possible connect dynamics microphones with impedance from 600 to 10 000 For the transmission it is possible to use Line Out with impedance about 600 Q The Line Out can be connected to microphone input of TRX or a rear panel con nector like PATCH IN Some transceivers has a feature that microphone input and rear panel input are interconnected so it is necessary disconnect the microphone during AFSK transmis sion because noise in hamshack could interfere with sound card signal Check your TRX instruction manual for particular interfacing Last thing you need to set up is audio levels of received and transmitted signal It can be made using operating system tools The level of transmitted signal should be about 2 3 of max level The signal could not be too attenuated or over excited and distorted You can detect it by monitor of outgoing signals For receiving signal you can set proper level directly on TRX and check the input level in your SSTV software 70 COMPUTER OPERATI
107. ided quality is suitable for SSTV An another option is a TV card with video input This possibility is more ex pensive because you must connect an external camera where the choices ranges from cheap CCTV black and white or color CCD cameras up to professional studio equipment 7 6 Software for Windows 7 6 1 List of programs 7 6 1 1 SSTV software Chroma Pix http www barberdsp com JVComm32 http www jvcomm de MMSSTV http mmhamsoft ham radio ch MSCAN SSTV Meteo http www mscan com Winskan SSTV32 http webpages charter net jamie 5 WO95SSTV http www barberdsp com w95sstv w95sstv htm VVVVVV TT 7 COMPUTER OPERATIONS 7 6 1 2 Digital mode software with SSTV support gt MULTIPSK http f6cte free fr index_anglais htm MixW http www mixw net 7 6 1 3 Software for dedicated interfaces This programs don t use sound card as modes but special interfaces Bonito Radiocom http www computer int com rc htm Roy 1 http www royl com dvb ham dvb 1 htm Wraase SC 4 http www wesacom de sstv 78 Ham radio image operations SSTV and radiofax broadcasting has their own rules as well as other communication modes If you already have a station equipped with some SSTV device and you are familiar with your SSTV software and have TRX interfaced with computer you can start your image operations The ideal beginning is to ask experienced operator for a first tes
108. iers in case of HamDRM An each subcarrier is modulated independently with quadrature amplitude modulation QAM and together with error correction code creates COFDM This modulation is well resistant to phase distortion attenuation selective fading and pulse interference The used modulation techniques are described later in section 10 2 2 117 10 DSSTV TRANSMISSION SYSTEMS Figure 10 8 The tuning spectroscope in DIGTRX Note three frequency peeks that is used as guidelines for proper tun ing Unlike RDFT which needs 3 partial operations coding recording of broadcast and decoding the HamDRM doesn t transmit data in whole block but the file is divided into separate segments so the image can be decoded and displayed during transmission HamDRM can be used in three basic modes The Mode A allows the fastest transmission but does not protect against the negative effects caused by selective fading The Mode B is slower than the first mode but is resistant against the negative impacts and it s much more robust The last mode is Mode E which is designed for communication through a channel with large delay and Doppler effect The QAM modulation is used with 4 16 or 64 states Modulation QAM 64 is the fastest but it needs a very good level of signal noise ratio at least 18 dB Modulation QAM 4 is slower but is more resistant to interference and requires a lower signal noise ratio about 5 6 dB Minimum SNR for QAM 16 shoul
109. ignal levels 800 Hz 128 6 25 Hz The lowest frequency is for black and the highest is for white the remaining 126 gray levels lay in the linear range between these two frequencies An issue with the transfer of more gray levels for example 256 levels is that it puts an increased demand on the demodulator The demodulator must be able to compensate for the frequency shift between the transmitter and the receiver In this case the distance between the two levels of brightness is 3 125 Hz and it is necessary to have a relatively large distance from the interference on the communication path to assure a pure transfer of all gray scale Normally we can settle for a less bright resolution where it is possible to choose the transfer of only 64 levels This requires less of the demodulator because it only needs to distinguish between 12 5 Hz steps True reproduction of colour images in gray scale is another issue Human vision cannot perceive the bright intensity of all three colour components at the same time When we watch three lights red green and blue of the same intensity the human 18 MODERN SSTV FEATURES 3 2300 Hz 1500 Hz A image scan line Figure 3 5 The scan line of BW image 1200 Hz perception considers the green light the brightest Red and blue are not as bright in our perception But a BW television camera only scans the level of intensity and therefore the resulting image would look like all
110. ing 150 150 150 151 151 151 151 152 152 152 152 152 153 153 153 153 153 154 154 154 154 155 155 155 155 156 156 157 161 161 162 165 165 168 168 170 171 Preface There are various methods used in transferring messages through radio waves With miscellaneous communication modes that are suitable for use under different condi tions varying in speed of transmission modulation or data protocol And many of them are used by radio amateurs to connect worldwide on short waves connections over satellite relays or message downloads from local packet ra dio BBS on very short waves The book you are about to read is about image transmission The most common method to transfer images is television broadcasting Fast Scan Television An analog FSTV broadcast can be produced in amateur conditions too Both picture and sound transmitted on amateur bands can be received via a regular TV set or by a satellite tuner in the case of frequency modulation These connections are held only on ultrashort or microwave bands because the signal needs a large bandwidth and thus the signal can be transported only through relatively small distances However the issue of this book is image transmission on short waves The most popular narrow band mode for image transmission is SSTV Slow scan Television Unlike the classic TV it can broadcast only static images with lower resolution An SSTV image is converted to an audio sign
111. ing device identifies which component it is currently receiving An important feature of using only one sync before beginning the color scan line sequence is that a converter will not replace the individual color components and degrade the color information In time intervals where the line sync is not transmit ted the gaps are filled with a reference level of black at 1500 Hz for 0 572 ms The second improvement has a substantial effect on image reception Unlike the Robot or SC 1 the detection of horizontal syncs is not necessary during reception And the broadcast between stations is fully synchronized The results of the use of such a system are sharper images and more contrasted edges Although the transmission conditions on the lower HF bands often do not allow the transfer of the image in 10096 quality old systems relying on line sync usually lose synchronization in such conditions The Martin system was originally implemented as a modification of the Robot 1200C converter and it preserves the transmission of the header gradation scale 36 FORMATS OF SLOW SCAN TV TRANSMISSION 4 2300 r1 TT T4 E 1900 E e O g S F 1500 By 1200 L 0 50 100 150 200 250 300 350 400 450 Time ms Figure 4 5 Scan line of Martin M1 when color bars are sent Robot 36s Color Martin M1 Figure 4 6 A comparison of systems in real conditions on the
112. ing the discrete Fourier transform So it s possible to modify image by using low or high pass filters or highlight certain components to affect the final look For specific case we can return to chapter 3 2 page 15 there is described how the SSTV transmission is affected by bandwidth The limited bandwidth caused the distortion of fine grid in resolution test pattern pic 3 3 Fine grid and sharp gradients in the image represent a high frequency components and limited bandwidth acted as a bandpass filter which suppressed the higher frequencies Also an image noise is represented by high frequency components and the low pass filter can be used for its reduction Vice versa a high pass filter is designed to highlight the edges and sharpening 13 3 1 Convolution matrix As one of the methods of linear filters is used the higher mathematic procedure discrete convolution A way the image is processed is given by convolution kernel which is given by matrix typically with dimensions 3 x 3 or 5 x 5 but also others The kernel moves pixel by pixel along lines and columns of the source image and computes pixel values see fig 13 6 It moves from first pixel on the position 0 0 165 COMPUTER IMAGE PROCESSING 13 Figure 13 5 COMPUTER IMAGE PROCESSING 13 Source Image Pixel values Output pixel value Convolution kernel 69 Figure 13 6 Computation of
113. ion in Hz because most SSB transceivers have smallest tunning step 10 Hz it is not possible to tune accurately The next parameter is clock rate difference it is caused by inexact sample rates 113 10 DSSTV TRANSMISSION SYSTEMS n o d B5 a g lt 250 590 820 1050 1280 1510 1740 1970 2200 2500 2750 3000 Frequency f Hz Figure 10 3 RDFT frequency spectrum RDFT Subcarrier RS code Redun Maximum Band Bit rate Symbol mode number dancy errors width rate Wyman 11 8 306 274 10 96 16 1840 Hz 866 bps 122 5 Bd Wyman 12 8 306 242 20 96 32 1840 Hz 165 bps 122 5 Bd Wyman 13 8 306 178 40 64 1840 Hz 563 bps 122 5 Bd Wyman 14 8 306 92 70 107 1840 Hz 291 bps 122 5 Bd Table 10 1 RDFT communication modes of sound cards and there is also small difference on receiver and transmitter side Both these parameters are dynamically found during transmission and they are used in demodulation process gt The next part is CODEBLOCK it is sequence of data frames of transferred file with redundancy symbols for error correction The transfer ends with TRAILER it contains mode identification like the first part The average bit rate of transfer is about 736 bps 92 bytes per second The input of demodulator are samples of RDFT signal the output are some phase states of each subcarrier The bloc
114. ion of an SSTV image is Most of the modes carry images with 240 lines and the image is displayed in a 4 3 aspect ratio on a screen We can then say that the number of columns is 240 x 4 3 320 This value then corresponds to a theoretical resolution but not a real image resolution The test chart fig 3 3 is used to qualify the horizontal resolution of images The resolution pattern contains alternating stripes of black and white in various densities from very rough to fine There is a comparison of this image with normal photography in fig 3 1 All SSTV modes in figure 3 3 have 320 columns But as we can see not all can transfer the image in actual quality The note in brackets describes the approximate time needed for the transfer of one pixel While with the Martin M2 we can hardly distinguish the second fine grid the M1 mode with double transmission time can transfer it without problems but its finest pattern is distorted Compare it to the real picture in fig 3 4 The last two modes listed have longer times of transmission and can transfer the finest details Unfortunately it is hardly compensated for by the slow speed of transmission 3 3 Line speed One of the most important parameters that is suitable for SSTV mode selection is the total time required to transfer an image Due to present transmission speeds SSTV is becoming similar to radio facsimile Therefore the mode parameters are not defined by horizontal and vertical s
115. ipment 6 1 Transceiver SSTV images can be received via a standard communication transceiver or receiver that covers the HF amateur bands and supports SSB modulation or a VHF trans ceiver with FM There is no need for further modifications although the IF filter should not be narrower than 2 5 kHz a width of 3 kHz is recommended The SSTV signal is taken from the audio output or headphone jack that is plugged into the SSTV decoding device For transmission a common HF or VHF transceiver with an SSTV signal con nected to the microphone jack should be used The band in which you are determines the usage of LSB or USB which is the same as in voice transmission No transmitter modifications are necessary But when operating SSB it is impor tant to realize that the broadcast of very loud speech can be achieved at approx imately of output power so the load of the output amplifier is fairly low and there is no danger of overheating But SSTV signals transmitted via a voice channel create a 100 load due to the presence of an auxiliary carrier SSTV transmission is not dangerous but it is advised to adhere to some safety measures 6 2 Station equipment for visual communication 1 Computer system a sound card or other special hardware interface and software 57 6 SSTV EQUIPMENT oL wm 0o00 O00 U o video SSTV digitizer modem Figure 6 1 SSTV station equipped for computer operations Curre
116. itter is a Moscow station RWM operating on frequencies 4 996 0 9 996 0 14 996 0 kHz with 8 kilowatts power So it can be nicely received in Eu rope Asia region Select CW mode and tune your receiver directly to one of station frequencies The unmodulated carrier is transmitted between 0 and 8 minute of an hour telegraphy identification goes from 9 minute and then the timing signal will continue Pulses in intervals 1 60 and 1Hz goes between 10 and 20 minute and 10Hz pulses goes between 20 and 30 minute This is repeated every 30 minutes The reception of WWV station is the next possibility This station broadcast timing pulses and announcement on frequencies 2 500 0 5 000 0 10 000 0 15 000 0 20 000 0 KHz and uses double sideband DSB modulation You can receive it with AM mode selected The WWV operates from the North America Fort Collins in Colorado The used power ranges from 2 5 to 10 kW There is yet another way with WEFAX station reception because these stations must have accurate timing too due to synchronous transfer The deviance error you should measure use to be expressed like absolute value of actual frequency e g f 11024 45 Hz or like deviance from f the A 0 55 Hz Some program this measure in parts per million ppm unit The ppm deviance can be computed 74 COMPUTER OPERATIONS 7 Calibrating the Sound Card with a Time Standard Broadcast Station button Clock 1 1024 45 Glock 1 1025 00 4 Acc
117. ize 4 2 0 formats after an interruption The chrominance syncs are separated from the scan line with 1500Hz gap that lasts 1 5 ms 2300 prend a F5 N 1900 H gt E 3 E T S 1500 M j 1200 0 50 100 150 200 250 300 Time t ms Figure 4 3 The scan line of Robot 72 Color when the color bars are sent The main disadvantage of the Robot modes lies in color coding because the receiver must be perfectly tuned to the SSTV signal Otherwise the image hue is distorted when the deviation is greater than 50 Hz For this reason Robot Research intro duced the transmission of gray gradation scale at the beginning of image transfer and the receiver device can auto tune for video signal The whole frame has 256 or 128 lines of which the first 16 or 8 lines are reserved just for gradation scale Some converters and PC software add some basic station info such as call sign and this part of the frame is called header The memory storage capacity of the Robot 1200C converter allows it to store an image with a resolution 256x240 pixels or four images with 128x120 and they are displayed in a 4 3 aspect ratio The fastest mode of the Robot family and the fastest color SSTV mode is the 12s mode It contains 120 lines transmitted in the 4 2 0 format Another mode is 24s with a 256x120 resolution and 4 2 2 color format The o
118. k circuit of demodulator is in fig 10 2 The delay block provides a delay of one symbol period Subtracting the angle values separated in time by one symbol period is the differential portion of this differential phase demodulator The average block averages 24 adjacent differences and divides by the unit phase step to produce the final demodulator output This averaging helps reduce the intersymbol interference produced by the low pass filters 114 DSSTV TRANSMISSION SYSTEMS 10 tuning receiver parameter demodulator extractor formater and outer encoder RS 306 x binary data file inner encoder amp transmitter modulator outer binary decoder data file inner decoder RS 8 4 Figure 10 4 RDFT communication channel lt low pass filter subcarrier frequency arctan sin x low pass filter delay L average Figure 10 5 The RDFT demodulator block diagram 10 1 1 RDFT operations The audio level of sound card is the most important setting on TX side It must be inside linear range it is usually the middle half of its dynamic range On RX side should be sound card level adjusted too The input signal should not be overdriven it causes unwanted nonlinearities The stations should be very precisely tuned to each other for making successful contact The station before the data transfer should send tunning signal This 115 10 DSSTV TRANSM
119. kBits compression 100 96 4 352 B Windows Bitmap RLE 100 3 984 B TIFF komprese LZW 100 3 850 B JPEG 25 3 766 B GIF 100 96 1 569 B JPEG 196 1 978 B Portable Network Graphics 100 1 111 B Table 9 4 Comparison of file sizes for different graphic formats 111 10 DSSTV transmission systems 10 1 Redundant Data File Transfer This communication mode uses phase shift keying PSK modulation The simplest PSK modulation changes subcarrier between two phase states BPSK biphase shift keying and these states corresponds to level of logical zero or one This is used for example for teletype mode PSK31 Data PSK Figure 10 1 Two phased digital PSK mod ulation RDFT uses similar principle but much more extended The signal is composed from eight subcarriers from 590 Hz to 2200 Hz with 230Hz steps Each subcarrier uses nine modulation states eight informational states and one state with no change meaning The data from inner encoder are used for phase assignment The first step in modulation process is to take a cosine of modulation angle plus 1400Hz subcarrier angle In next steps the energy around 1400 Hz is isolated and translated onto right subcarrier Then the subcarriers are compiled together and resulting spectrum of signal is in fig 10 3 The signal contains two levels of error coding The outer coding scheme use RS code 306 z where z is set by level of error control see tab 10 1 The s
120. kW NMG 8 503 9 kHz 120 576 4 kW NMG 12 789 9 kHz 120 576 4 kW NMG 17 146 4 kHz 120 576 4 kW 12 00 20 45 Broadcast time 00 00 08 45 12 00 20 45 12 5 8 Boston Massachusetts USA Ident Frequency lpm IOC Power Note NMF 4 235 0 kHz 120 576 4 kW 02 30 10 28 NMF 6 340 5 kHz 120 576 4 kW NMF 9 110 0 kHz 120 576 4 kW NMF 12 750 0 kHz 120 576 4 kW 14 00 22 28 154 LIST OF PROFESSIONAL STATIONS 12 Broadcast time 02 30 10 28 14 00 22 28 12 5 9 Inuvik Canada Ident Frequency lpm IOC Power Note VFA 8 457 8 kHz 120 576 1 kW 02 00 16 30 Broadcast time 02 00 16 30 12 6 Australia and Oceania 12 6 1 Charleville Australia Ident Frequency lpm IOC Power Note VMC 2 628 0 kHz 120 576 1 kW 09 00 19 00 VMC 5 100 0 kHz 120 576 1 kW VMC 11 030 0 kHz 120 576 1kW VMC 13 920 0 kHz 120 576 1kW VMC 20 469 0 kHz 120 576 1 kW 19 00 09 00 Broadcast time continuous 12 6 2 Wiluna Australia Ident Frequency lpm IOC Power Note VMW _ 5 755 0 kHz 120 576 1 kW 11 00 21 00 VMW 7 535 0 kHz 120 576 1 kW VMW 10 555 0 kHz 120 576 1 kW VMW 15 615 0 kHz 120 576 1 kW VMW 18 060 0 kHz 120 576 1 kW 21 00 11 00 Broadcast time continuous 155 12 LIST OF PROFESSIONAL STATIONS 12 6 3 Wellington New Zealand Ident Frequency lpm IOC Power Note ZKLF 3 247 4 kHz 120 576 5 kW 09 45 17 00 ZKLF 5 807 0 kHz 120 576 5 kW ZKLF 9 459 0 kHz 120 576 5 kW ZKLF 13 550 5 kHz 120 576 5 kW ZKLF 16 340 1 kHz 120 576 5 kW 21
121. lack then they do not affect the image information All frequency components of SSTV are inside the low frequency band and it is possible to transfer them via voice channels Other SSTV modes came out from this original standard and in most cases they differ only in scan speed and in the addition of color transmission 11 Modern SSTV features A milestone between methods of old and modern SSTV image transmission is with out doubt the usage of semiconductor memory chips The creation of the first converters between fast and slow scan television signals was credited to the exis tence of permanent image storage in memory Consequently image transmission could be improved because the usage of long persistence CRTs which had been a major constraining fact was now eliminated Due to it some new formats with longer transmission time were developed They brought more quality to black and white transmission and helped to develop colour image transmission There was a trend in the design of new formats that created several modes in each system There were modes with faster transmission and lower resolution and on the other hand modes for the transfer of higher quality images but longer time length There is a possibility to change between them according to the actual band condition The early phases of development were influenced by two companies the American Robot Research Inc and the German Wraase Electronic led by radio amateur Volker
122. ld curve in the middle and move the control point upwards and 164 COMPUTER IMAGE PROCESSING 13 if you move the point more to the left or right you can change brightness of darker or lighter tones In example 13 5B are lighter tones made more brighter and the lower end of curve is moved to the right so darker pixel are more darker and the image is more contrasted For image darkening move the point downwards it s in example 13 5C also there is moved the right edge of the curve so lighter pixel are more brighter now For changing contrast use the curve in 13 5D there are two control points The curve with S shape makes dark tones darker and light tones brighter In addition to basic editing the curve can be used for a variety of effects see example 13 5 The shape is little crazy and result image lost real tones Notice that there is inversion of dark tones in left part of the curve The curve and histogram adjustment is possible to do for image luminance and for each color component too so it is possible to change color perception of an image 13 3 Filters Images can be further improved using various filters They can serve different pur poses mainly for smoothing and noise reduction increasing sharpness edge detec tion unsharp masking etc Digital image itself is a discrete two dimensional 2D signal which is character ized by its frequency spectrum whose components similar to the 1D signal can be determined us
123. lexing OFDM OFDM is a representative of the modulation scheme with multiple carriers MCM Multicarrier Modulation Thanks to its properties the OFDM found application in many modern technologies i ee ADSL WiFi IEEE 802 11a g networks WiMAX and standards for digital broadcast and terrestrial digital television DVB T etc OFDM has very good spectral performance and it is resistant to pulse interfer ence because transfered information is dispersed in wide frequency spectrum so interference disturb only few nearby symbols It s also resistant to inter symbol in terference fade outs caused by multipath spreading and has low sensitivity to errors in time synchronization 123 10 DSSTV TRANSMISSION SYSTEMS HR CON EOOON ED Input data N W Signal I LOL Signal Q Soe Signal QAM W LA GO LA LZ Time t Figure 10 12 The example of QAM 16 modulation for input data sequence The OFDM generates a huge number of subcarrier waves and in case of HamDRM there are for best performance only 57 subcarriers Many other applications like digital video broadcast or wideband data communication uses hundreds or thousands of subcarriers These subcarriers have very small distances even those that the overlap the range of others
124. mage buffer and 10 JPEG compressed images The JPEG memory has a battery backup so it is possible store images when the unit is switched off The converter has an RS232 interface for computer connection 115 kbit s The input and output for external video signals is only NTSC VC H1 is powered by four AA batteries or external DC supply with 6 0 V The maximum consumption is 650 mA when digitizing an image otherwise the consump tion is 450 mA when the LCD is on or 100 mA in stand by mode with the LCD off Figure 6 8 Mobile SSTV converter VC H1 Supported modes Martin M1 M2 gt Scottie S1 52 Robot Color 36 72 gt AVT 90 94 gt FAST FM 65 Computer operations In one afternoon an equipped hamradio operator can begin receiving SSTV AII that is needed is to make a connection cable between a transceiver and a sound card and download some SSTV related software Then tune into 14 230 MHz USB for 24 hour a day SSTV activity Programs for SSTV operations are very similar and provide equivalent basic functions of course with different comfort levels Some of them are intuitive and well arranged while others require studying a manual Everybody has the possibil ity to choose from more variants and see what is best for him and what provides requested functions Every operator must know these basic functions to configure an accurate sampling frequency for reception and transmission to set proper sound card
125. mage slant for 0 01 96 timing difference in fig 7 9 If a transmitting station has higher timing and reception lower the image slants to the right 7 9a in opposite situation to the left 7 9b However timing derived from sample rate is not used to be exactly 11 025 00 Hz but often can differ up to few tenths of percent for each peace of hardware For speech and music processing it doesn t matter but in free run transmission of SSTV it causes problems 73 7 COMPUTER OPERATIONS P LO LE SBB EN Hn BUE bpn I 1 LJ LT IE U Slow Scan f Television IM i Imm EE SSK SSG AURURCECACURUR a Opposite station b Opposite staion has higher timing has lower timing Figure 7 9 Image slant distortion when inaccurate timing is used for free run modes All SSTV program are equipped with a tool for the timing configuration It is possible to receive SSTV signal from a band and by an edge of received image set the timing program will automatically compute timing deviation This way has a disadvantage because not all SSTV stations has proper transmit timing This is caused by offset between receiving and transmitting timing Much more precise way is use of shortwave broadcast of timing normal Programs are equipped with special reception option which displays spectrum in a second cycles For timing setting just tune to the frequency of broadcast and leave to plot received pulses for several minutes The usable transm
126. mile transmission modes 11 2 2 1 Facsimile transmission modes 11 3 Professional stations There are dozens of stations operating on high frequency bands It depends on 135 11 FACSIMILE RADIOFAX your location some of them are well catchable all day others only when conditions improve Broadcast images are in most cases a variety of meteorological maps synoptic charts graphs of pressure and altitude direction of wind weather forecasts cyclone or typhoon warnings retransmissions of satellite imagery and broadcast of news agencies Even today when Internet is almost everywhere the fax broadcast has still its foundation The main customers are naval ships military remote airports and islands where the shortwave transmission is only way how to get actual information They are often very important because station distributes also weather warning of upcoming storm and hurricanes Each station has given its daily broadcast schedule for example see 11 6 You can find here what images will be transmitted in a time of day FLEET WEATHER AND OCEANOGRAPHIC CENTRE NORTHWOOD ENGLAND AMENDED B14A RADIOFAX SCHEDULE WITH EFFECT FROM 1900012 JAN 05 PIME PRODUCE 700000000 iP FE PRODEST mmm eem een ene mantener mn HUN ALL TIMES IN ZULU gt o ieu g za 0000 18Z SFC ANALYSIS 1200 062 SFC ANALYSIS 0012 18 SFC PROGNOSIS T 24 1212 06 SFC PROGNOSIS T 24 0024 182 850MB WBPT PPTN T 24 1224 062 850MB WRPT PPTN
127. n the images should be distorted due to loss compression techniques but you can control the degree of it There is no constrain in image resolution it is given by image file parameters Only constrain is the bandwidth of SSB channel and the resulting maximum data rate and the time required for transmission There are also bigger requirements for stations equipment in comparison with classic SSTV You need better computer at least 1GHz CPU and 256 MB RAM In your ham shack you can use without any problems an oldish computer e g Pentium 150MHz for digital modes like RTTY or PSK packet radio and analog SSTV but algorithms of signal processing for DSSTV is so complex that a slow 150MHz Pentium would not be able to process signals in real time 94 INTRODUCTION TO DIGITAL SLOW SCAN TV 9 Also there are increased requirements on the transceiver used Used modulation techniques use the maximal width of the communication channel and SSB trans ceiver without the linear range of SSB channel isn t usable for DSSTV Of course there must be switched off any additional signal and modulation filters speech processor equalizer Sound card interfacing is same as for classic SSTV the connection between TRX and sound card is enough Output level of sound card should be about 1 3 of max imum switch off software AGC When signal is overexcited the intermodulation causes disproportionately large signal and distortion and the signal cannot be
128. n input for an 25 3 MODERN SSTV FEATURES MSB LSB Meaning P 6 5 4 3 2 1 0 0 0 Color composite video 0 1 BW red component 1 0 BW green component 1 1 BW blue component 0 Horiz resolution 128 160 pixels 1 Horiz resolution 256 320 pixels 0 Vertical resolution 128 120 lines 1 Vertical resolution 256 240 lines 00 0 Robot 00 1 Wraase SC 1 0 110 Scottie Wraase SC 2 U 1111 Scottie Wraase SC 2 1 0 40 AVT Scottie DX 1 01 AVT PD 11 0 PD 1 1 1 Pasokon TV X Parity bit Table 3 1 The meaning of bits in VIS code electronic station log Unfortunately these additional signals have no standardized format and they are not compatible with other SSTV programs Some of them append the data transmission to the first scan line image ChromaPix or even prior to broadcast of VIS WinPix MMSSTV Some newly developed SSTV systems do not use standard VIS code with 8 bits and send 16 bits MP MR ML modes or use odd parity for error checking This is because of 27 from which 128 possible combinations of the VIS code is almost exhausted Differences in these and other systems will be described in further chap ters 26 MODERN SSTV FEATURES Mode decimal hexa binary Martin M1 44 Ox2C 0101100 Martin M2 40 0x28 0101000 Robot 36 colour 8 0x08 0001000 Robot 72 colour 12 0xOC 0001100
129. n late 1998 and 1999 The project anticipated broadcast on the frequency 437 975 MHz but due to some problems with antenna systems we have to make do with only the occasional broadcast on the two meters band Transmit frequency was 145 985 MHz FM Dopplers s frequency shift The packet radio AX 25 BBS ROMIR 1 was normally operating on this channel Station at low orbit passed 5 times a day over Europe at approximately 1 5 hours intervals The Robot 36 Color mode was chosen for SSTV transmission The pictures were sent in 2 minutes interval so during one orbit you could copy transmission for 10 minutes and receive about 5 pictures Each picture was introduced by morse code lad e DE ROMIR and then transmitted Figure 8 3 SSTV picture form station ROMIR 90 HAM RADIO IMAGE OPERATIONS 8 I found that there was about 5 kHz frequency change caused by Doppler s effect So during orbit it is good to tune receiver it s ideal to use transceiver with con tinuous FM tuning I use FT 767 When Mir approached the horizont and it was coming near the tunning frequency was 145 990 MHz and when it was fly away the frequency is lower i 145 980 MHz Some transceivers measure discrimination of FM signal so it is very easy to tune on carrier frequency Designers of SSTV station chose Robot 36 Color mode it s not resistant to noise so when there is great shift from center carrier frequency the signal used to be noisy and
130. nal AVT software was capable of image reconstruction in this case Because the image data is completely synchronous the data simply has to be shifted in memory until the RGB data is aligned correctly and then the image comes out perfectly Again the AVT system provided means to hot reconfigure the data after reception So reception without after sync header worked fine The earlier listed options for each mode can improve its performance The first is the narrow band transmission which uses a 400 Hz band from 1700 Hz black to 2100 Hz white With an appropriate filter the resistance to interference can be improved with minimal loss of image quality For instance the 400 Hz wide CW filter can be used with a variable IF shift The second option is the QRM mode where an entire image is sent interlaced Within the first half of image transmission time half of the scan lines every odd one is sent Then the scan loops back to the beginning and sends the remaining half lines even lines The fact that some of the disturbed lines of the first field is interlaced with fine lines received from the second will definitely improve the overall subjective impression of image quality The original AVT software also contains tools for handy image improvement it is possible to select distorted lines and the program will reconstruct them by averaging neighborhood lines It is also is possible to shift the second field horizontally independently of the fi
131. nalog information C facsimile The 132 FACSIMILE RADIOFAX 11 transmitter modulates the frequency of carrier in the range 4 400 Hz on shortwaves and 4 150 Hz on long waves This range is called signal deviation The fax signal can be created by direct modulation of broadcast frequency or by frequency modulation of subcarrier 1900 Hz Then the transmitter changes frequency between black and white colour Black color corresponds to 1500 Hz and white 2300 Hz The amplitude modulation AM used for image transmission on VHF and mi crowave meteo satellite downlinks There is used positive AM and level of modu lation determines the brightness For black colour it is 496 level and for white it is 90 to 100 The negative modulation inverts levels the minimal value is for white and the maximal value for black Most commercial stations use APT Automatic Picture Transmission for a fully automated reception without requiring the presence of an receiver operator The image transmission begins with start tone when transmitter modulates the carrier with some frequency mostly 300 Hz changing the maximal levels of modulation 300x in a second This signal is recognized be the receiving device and it switches from stand by mode to working mode and waits for phasing signal Starting APT signal Phasing signal i Image edge T RER LORE WGA Figure 11 3 The start of facsimile transmission The phasing signal is used for sy
132. nchronization and it is broadcast few second before an image Normally consist of rows of 95 black and 5 white It generats a vertical white line which identifies the edge of the transmitted image After the end of image transmission another APT signal is sent it has modulation 450 Hz and switches the receiving device back to stand by mode 11 2 2 The reception Shortwave facsimile reception can be realized by using upper single sideband USB receiver For this reason you ll have to tune on the frequency which si about 1900 Hz below the station frequency So if the station uses frequency 3855 0 kHz you must tune in USB on 3853 1 kHz i e 1900 Hz below All facsimile reception software is equipped by spectroscope the same as for SSTV so precise tuning should not be a problem You can control tuning by the fact that the largest portion in the fax image is mostly white 133 11 FACSIMILE RADIOFAX Figure 11 4 Modern receiver Sony CRF V21 for WEFAX and RTTY reception equipped with printer There are still used analog WEFAX receivers with electromechanical printers but in our case we can use only PC with sound card and proper software The most important parameters of the transmission are the speed and index of cooperation IOC The IOC relates with a horizontal scan rate and can be converted to number of pixels by simple formula line m x IOC pixels The most frequently used IOC is 576 1810 pixels then 288 9
133. ne speed The American 60 Hz 8s norm has a transfer speed of 900 0 lpm The line speeds for new modes were chosen at 600 0 lpm for 12s mode with 120 lines and for 24s mode with 240 lines The mode with the best resolution has a line speed of 400 01pm and a total transmission time of 36 seconds The Robot SSTV system reserves the first 16 or 8 lines for a 240 or 120 line image for gradation gray scale The scale can be used to tune the signal more precisely Although Robot Research cooperated with Copthorn MacDonald they ignored the trend in amateur construction of digital converters with doubled modes Despite this fact Robot system and its converter Robot 300 became quite popular even with a price tag of over 800 in the mid seventies During the 70 s and 80 s the ham radio market was not the only outlet for SSTV converters but the companies found opportunities in the telecommunication market and sold SSTV monitors and cameras as devices for image transmission over telephone lines 4 1 2 BW transmission with computer software An example of B amp W mode implemented with computers is the AVT 125 BW mode of the Amiga Video Transceiver system and it is suitable for good quality image transfer in circa 2 minutes The mode has a vertical resolution of 200 lines because the Amiga computer resolution was 320x200 The AVT system is different from the previous B amp W modes because it has no line sync like WEFAX The transmission is based on a fully
134. ng circuits reads short samples from each line during each camera scanning beam cycle All the samples from scan lines of the FSTV camera create one scan line of slow scan TV picture In the next scanning beam cycle the sampling position moves to the left and creates the next scan line The cycle is repeated until the whole picture is sampled The next type of image scanner often used was a scanner with a photomulti plier for the scanning of transparent or non transparent originals FSS Flying Spot Scanner The light through transparent originals falls on the photomultiplier whose output is a voltage that is proportional to the transparency of the original This creates an amplitude modulated video signal which can be converted to the frequency modulated signal of SSTV The electromechanical scanner was used for non transparent originals which were scanned from a rotating roller The mechanical part was assembled from a roller with the mounted original a screw thread for sliding and a drive unit with a synchronous motor The second part consisted of a lens a light bulb a photo transistor and sensor circuit for the generation of the SSTV signal 6 4 Early FSTV SSTV converters SSTV FSTV converters usually sample and digitize incoming SSTV signals and store them in memory Simultaneously the memory content is read and converted to an analog signal which controls the fast scan TV modulator The received SSTV signal is limited to the const
135. ngly suppressed so the frequency of white colour the maximal level of an SSTV signal was chosen at 2 300 Hz SSTV signals are transmitted via frequency modulation of an audio signal To avoid any phase shift and drift which both have negative impact on picture qual ity the spectrum of video signal is modulated on the auxiliary carrier frequency 1900 Hz sub carrier This modulation method is called Sub carrier frequency mod ulation SFCM The frequency of video signal varies from black by gray shades to white The bandwidth needed for SSTV transmission varies in the range of 1 0 to 3 2 kHz and depends on the SSTV mode transmission speed and also on image content see fig 3 1 Cheap modems based on Hamcomm do not use perfect continuous harmonic signals but also create the quantized signal Step changes between quantization levels require wider bandwidth so some image details can get lost The emission classification code for the SSTV mode is J3F which means gt J Carrier modulation Single sideband with suppressed carrier gt 8 Nature of modulating signal One channel containing analogue information F Detail of signal television signals In the case of an SSTV transmission via a frequency modulated FM channel emission is classified as F3F and A3F for amplitude modulation AM with both side bands 14 MODERN SSTV FEATURES 3 30
136. nitors were the most important SSTV equipment in the seven ties There were other commercial products available but most homemade monitors were built by SSTV enthusiasts 58 SSTV EQUIPMENT 6 SSTV GL dn ooo nnn converter ooo 0000 Figure 6 2 An SSTV station equipped with a stand alone SSTV converter Figure 6 3 Monitor Robot Model 70 and camera Model 60 from Robot Research Inc Products from Robot Research Inc Wraase Electronics and Venus were very popular These products were not produced for just the ham radio market but were also found in the image communication over telephone lines markets A typical monitor consists of several basic parts see fig 6 4 input and limiter circuits video and sync detectors scanning circuits cathode ray tube drivers and power supply The long persistence CRTs are made with special photoluminescence phosphor In simple terms phosphorescence is a process in which the energy ab sorbed by a substance is slowly released in the form of light These CRTs were most used in radar displays or oscilloscopes for the monitoring of slow processes The path of frequency modulated signals that contains video and syncs goes through the limiter where the signal is limited to constant amplitude and then flows into image discriminator There are video detecting circuits for syncs and 59 6 SSTV EQUIPMENT video separation here Then signals from the discriminator are amplified and dri
137. ntly the most common SSTV device is a personal computer with a sound card There are a number of programs for personal computers with Windows Mac GNU Linux and DOS There are also special modems MFJ Royl AOR TDF370 or the very simple Hamcomm modem Hamcomm is based on a simple comparator circuit and connected to the RS232 serial port But it is only usable for old DOS based software The most varied software options are for Windows and a sound card Additional equipment can be used such as a web camera or a television card with analog video input 2 Digital scan converter is a stand alone device that digitizes received signals and stores them in memory The decoder converts memory content to analog signals PAL or NTSC for display on a normal TV set or monitor The converter can be connected to any color or monochrome camera which then transmits live images Due to digital data processing most converters are equipped with a computer interface This allows for the addition of texts to images and the upload and storage of images to from computer Tape recorders were historically often used to record SSTV and for storing QSO images 3 Long persistence CRT monitor and circuits for signal filtering and vertical and horizontal drives etc The usage of these monitors is long over Electro mechani cal scanners or sampling cameras were used as SSTV signal sources in these days 6 3 Historical tidbits 6 3 1 SSTV monitor Long persistence mo
138. ny gap Then there is a second luminance Y gt The exact timing of modes is gt PD 50 286 us pixel gt PD 180 286 us pixel gt PD 90 532 us pixel gt gt PD 240 382 us pixel gt PD 120 190 us pixel gt PD 290 286 us pixel gt PD 160 382 us pixel YCrCb color coding needs accurate signal tuning to prevent color distortion Thanks to a wide horizontal sync it is possible to detect frequency deviation and compensate color distortion There is also gray scale on the top of image for tuning detection The main advantage is reduced transmission time compared with RGB modes The PD 290 mode supports a resolution of 800x600 and its transfer time is nearly five minutes although at the cost of little color loss Some modes have resolutions of 640x480 while PD 160 has 512x384 The fastest two minute PD 120 has a worse image quality but in many cases it is still sufficient Beside the five modes with high resolution the system includes two with standard resolution PD 90 uses 320x240 and has a better image quality than Martin M1 or Scottie S1 because it is based on a longer transmission time per pixel The last mode is the very fast PD 50 which provides a similar resolution as Scottie 52 4 4 Experimental modes During the years of the SSTV boom many modes were created but never gained popularity Many of them are totally forgotten like WinPix GVA Proscan J 120 WA7WOD system or ScanMate although some of them ha
139. o operators reported only weak signals and was monitored only couple of days Probably due to low temperature the on board batteries lost capacity The SuitSat AO 54 should starts the series of similar experiments like project Arissat 1 91 8 HAM RADIO IMAGE OPERATIONS Figure 8 4 SuitSat built into the spacesuit NASA source cat no ISS012E15666 8 6 3 Amateur Radio on the International Space Station The successor of popular ham radio projects on Mir is the project ARISS The targets are to build SSTV beacon repeater packet radio BBS and world wide propagation 92 HAM RADIO IMAGE OPERATIONS 8 of ham radio hobby The SSTV equipment on ISS consist of SpaceCam 1 software from ChromaPix authors It runs on normal PC support video digitizer and it can works as repeater or transmits slide show pictures from station cameras The SpaceCam transmit pictures every 120 seconds in Robot Color 36 mode and every picture is started with morse identification ROISS NA1SS The following frequencies are currently used Voice and Packet Downlink 145 800 MHz Worldwide Voice Uplink 144 490 MHz for Regions 2 and 3 The Americas and the Pacific Voice Uplink 145 200 MHz for Region 1 Europe Central Asia and Africa Packet Uplink 145 990 MHz Worldwide Crossband FM repeater downlink 145 800 MHz Worldwide Crossband FM repeater uplink 437 800 MHz Worldwide Worldwide SSTV downlink 145 800 MHz VVVVVVV F
140. odes did not gain popularity like other modes The AVT modes are practically not in use today A reason for this could be the fact that the manufacturer wanted to keep the image scan parameters of the system secret However by intercepting signals and reverse engineering the parameters of the AVT modes were implemented in other devices by the SSTV community This was done without the additional software tools that made the AVT unique The AVT system contains four line sequential RGB modes and one B amp W The scan lines have no gaps between color components and a really unusual thing is that the modes do not use any horizontal sync Another unusual feature is the mandatory function of vertical synchronization that is sent as a digital header before the image transfer begins The AVT family contains 5 modes and each of them has the following four options 1 Default variant is the same as conventional SSTV modes but does not have any line syncs 2 Narrowband variant uses shorter band for video signals from 1700 Hz for black to 2100 Hz for white QRM variant that uses picture interlacing just like in analog television 4 The combination of the QRM and narrowband variant eo The fastest mode is the AVT 24 with 120 lines and it is transferred for 31 seconds The next mode is AVT 90 with a resolution of 256x240 and an image quality slightly worse than in the Martin M1 ATV 90 sends each color component in 125 0 ms thus the speed is 2
141. of Y CrCb colour transmission used in SSTV The first for mat 4 2 2 transmits both chrominance signals within half the time in comparison with Y in one line The second format 4 2 0 contains only one chroma signal Odd scan lines could include for instance R Y and the even scan lines could be B Y The chrominance signal is then given by the average of two consequent scan lines of the original image The advantage of this type of transfer to RGB is significantly shorter transmission time In comparison to RGB transmission Y CrCb takes approximately half the time yet guarantees almost the same image quality Its disadvantage compared with the RGB model is a loss of image information which is higher when the 4 2 0 format is used Also precise transceiver tuning is needed otherwise the colour information will be distorted This is the reason why the Y CrCb encoding is used less frequently According to the positive or neg ative deviation from the carrier the image is strongly hued to pink or green see figure 3 9 Figure 3 9 Color distortion of YCrCb when the station is improperly tuned The transmission for colour FSTV uses YCrCb and also uses special methods and modulation in PAL SECAM to eliminate this colour distortion which can occur on the transmission path Unfortunately this feature does not exist in SSTV and so the result of selective fading can cause colour ghosts in image SSTV systems using YCrCb transmission ar
142. oma Italy 12 1 4 Moscow Russia 12 1 5 Murmansk Russia 12 1 6 Northwood The United Kingdom 12 2 Africa 12 2 1 Cape Naval South Africa 12 3 Asia 12 3 1 Beijing China 12 3 2 Beijing China 12 3 8 Shanghai China 112 112 115 RE 120 121 123 124 126 126 128 130 130 131 132 133 135 135 138 140 142 142 143 143 144 147 147 147 147 147 148 148 148 149 149 149 149 149 150 12 3 4 New Delhi India 12 3 5 Tokyo Japan 12 3 6 Pevek Chukotka peninsula 12 3 7 Taipei China 12 3 8 Seoul Republic of Korea 12 3 9 Bangkok Thailand 12 3 10 Kyodo News Agency Japan 12 3 11 Kyodo News Agency Singapore 12 3 12 Northwood Persian Gulf Base 12 4 South America 12 4 1 Rio de Janeiro Brazil 12 4 2 Valparaiso Playa Ancha Chile 12 5 North America 12 5 1 Halifax Nova Scotia Canada 12 5 2 Iqaluit NWT Canada 12 5 3 Resolute NWT Canada 12 5 4 Sydney Nova Scotia Kanada 12 5 5 Kodiak Alaska USA 12 5 6 Pt Reyes California USA 12 5 7 New Orleans Louisiana USA 12 5 8 Boston Massachusetts USA 12 5 9 Inuvik Canada 12 6 Australia and Oceania 12 6 1 Charleville Australia 12 6 2 Wiluna Australia 12 6 5 Wellington New Zealand 12 6 4 Honolulu Hawaii USA 12 7 List by frequency 13 Computer image processing 13 1 Image resizing 13 2 Color adjustment 13 3 Filters 13 8 1 Convolution matrix 13 3 2 Noise reduction 19 3 2 1 Spatial average filtering K Median filter 13 3 8 Sharpen
143. ons which are used in most common programs Although some functions below are shown in GIMP see sec it should not be problem for savvy user to find same functions in his favourite editor Later see section there are specific tutorials only for GIMP 13 1 Image resizing The SSTV uses a relative small resolution in comparison with images you can get from digital cameras scanners or some internet galleries So before transmission the image should be resized to conventional resolution 320x240 pixels You can achieve this in almost all SSTV programs but images sometimes haven t aspect ratio 4 3 or we want use only part of image So it is useful to prepare your images before QSO The image resizing brings a little risk see image 13 1 original image is test chart on page 172 There is a result of two image scaling algorithms The left image was scaled down by nearest neighbor interpolation when pixels in regular columns and rows are removed But the linear interpolation was used for the right image The difference is visible on the first sight the nearest neighbor method caused distortion and some 161 13 COMPUTER IMAGE PROCESSING Figure 13 1 Results of image resizing with two different algorithms details are lost completely e g thin lines are lost and on originally smooth curves are stair like lines more evident The linear interpolation is more considerate to details but it depends on amount of decreasing and som
144. ontrolled synchronous motor Broadcast material is attached to the cylinder which rotates in a constant speed A small ray of light is focused on the broadcast medium map text photos etc The light reflected from the medium is processed by a photoelectric sensor The sensor bears the light source photocell and moves along rolled in a constant speed The sensor moves from one end to the other and captures the image line by line Voltage difference from the photo sensor are amplified and it is used to modulate the signal carrier direction of rotation NNW a wt NL UK NU m photo cell exciter lamp Figure 11 2 The principle of an electromechanical image capture The fax transmission on shortwaves has only few similarities with the fax machines you know from home and offices The fax transmission is based on CCITT recom mendations Facsimile CCITT Group 1 T 2 of 1968 the short wave recommenda tion is described chapter 11 6 The CCITT recommends the frequency 1500 Hz for white and 2300 Hz for black In North America it is 1500 Hz for white and 2300 Hz or 2400 Hz for black The transmission speed is 1801pm The fax machines of this type could be adjusted for amateur operation The later recommendations T 3 T 4 or T 30 can not be used on HF and there are used in telephone lines The frequency modulation F3C is used for shortwave transmission F frequency modulation 3 single channel containing a
145. or can start reception and direct yagi thanks to several instances it isn t necessary to record the transmission from beginning to end when reception failed only bad segments can be repeated not whole transmis sion main disadvantage of HamDRM is that the powerful PC configuration and OS better then Windows 2000 is a must V NV V M M 10 2 2 Quadrature amplitude modulation QAM Quadrature amplitude modulation QAM uses amplitude and phase modulation together HamDRM for each subcarrier OFDM cells can use several modula tion schemes which differ in number of modulation states QAM 4 QAM 16 and QAM 64 The number of modulation states QAM m is divided into m states for phase keying and ym amplitude levels Thanks to multistate modulation it is not required 121 10 DSSTV TRANSMISSION SYSTEMS so huge bandwidth on the other hand a growing number of states of modulation makes the signal less resistant to interference pulse amplitude modulation low pass I cos 2rift filter circuit frequency QAM signal pulse amplitude modulation low pass filter Q sin 2nft Figure 10 10 The QAM modulator An modulation state is created from combination of amplitude and phase which can define a bit word of length l For QAM 4 is the word length I log m log 4 2 for QAM 16 is 4 and for QAM 64 it is 6 The modulation changes between these states A 2k 1 m pro k 1 2 m
146. or latest ARISS news and status check the website http www ariss org 93 Introduction to digital slow scan LV The development of computers and new opportunities which gives us the use of powerful processors and sound cards modems have resulted in the design of new com munication modes One of these modes is the digital slow scan television DSSTV which allows transmission of images without any loss of quality We have two choices for digital image transmission The first system is RDFT Redundant Data File Transfer which is the result of several years of creative efforts of Barry Sanderson KB9VAK and a group of ham radio enthusiasts The second system is called Digital Radio Mondiale DRM It s open standard for digital broadcast on short waves It was developed by DRM Consorcium and was standardized by organizations ITU IEC and ETSI The DRM system is used mainly by short wave broadcast stations and its modification for ham radio purposes is called HamDRM It is possible to use these modes also for transfer of any types of files text sounds software instead of images The difference between analog and digital SSTV is huge There are used entirely different modulation principles and essentially some files in JPEG JPEG200 PNG etc formats are sent Also the error correction and detection is implemented using Reed Solomon code The result is that image is transfered without any distortion means transfer distortio
147. ower Note CFH 122 5 kHz 120 576 10 kW CFH 4 271 0 kHz 120 576 6 kW CFH 6 496 4 kHz 120 576 6 kW CFH 10 536 0 kHz 120 576 6kW CFH 13 510 0 kHz 120 576 6kW Broadcast time continuous 12 5 2 Iqaluit NWT Canada Ident Frequency lpm IOC Power Note VFF 3 253 0 kHz 120 576 5 kW 21 00 23 30 VFF 7 710 0 kHz 120 576 5 kW 00 10 09 00 Broadcast time since middle of June till the end of November 12 5 3 Resolute NWT Canada Ident Frequency lpm IOC Power Note VFR 3 253 0 kHz 120 576 5 kW 00 10 09 00 VFR 7 710 0 kHz 120 576 5 kW 21 00 23 30 Broadcast time since middle of June till the end of November 12 5 4 Sydney Nova Scotia Kanada Ident Frequency lpm IOC Power Note VCO 4 416 0 kHz 120 576 11 21 11 42 17 41 VCO 6 915 0 kHz 120 576 22 00 23 31 Broadcast time by frequency 153 12 LIST OF PROFESSIONAL STATIONS 12 5 5 Kodiak Alaska USA Ident Frequency lpm IOC Power Note NOJ 2 054 0 kHz 120 576 7 5 kW NOJ 4 298 0 kHz 120 576 7 5 kW NOJ 8 459 0 kHz 120 576 7 5 kW NOJ 12 412 5 kHz 120 576 7 5 kW Broadcast time 04 00 11 59 16 00 00 18 12 5 6 Pt Reyes California USA Ident Frequency lpm IOC Power Note NMC 4 346 0 kHz 120 576 4 kW 01 40 16 08 NMC 8 682 0 kHz 120 576 4 kW NMC 12 786 0 kHz 120 576 4 kW NMC 17 151 2 kHz 120 576 4kW NMC 22 527 0 kHz 120 576 4 kW 18 40 23 56 Broadcast time continuous 12 5 7 New Orleans Louisiana USA Ident Frequency lpm IOC Power Note NMG 4 317 9 kHz 120 576 4
148. p yet and Kyodo News Agency still distributes newspapers via facsimile 5 ERK 2 AOC BRE BRSOKLS CAVES MRU 2A BER Bee SO EEEL CHRD ERY CATT SERRE ARAN CORO CinA Oi E WE ZEBLLBRNEL APR GB MCT STRRREMCX WELLS FERCFAXRA W AXI03 6252 8805 Ex f compas8 kyeodenews jp GHEE 17 RD 2 KYODO NEWS muss ZSEE TAZE OKRESY wus TABA GNER an 1 2lkbsnnDEEKDe KERKE TAR BASFRE _ POGIRIGEUHEIHOT aJgEUOPBE NU R PEL BERS eee ised tain SKaR m ESKI a A 3 ZBEEZTO BZZGRUBZKUE K RERSRNBR vette HAE TTT ni DI ela RoOSBINU IRE ZIE A5 H DE M BEGGS IEA FE SE y munt EEE ER Totbstrr bH Bs eae Peace sibus nus ir b RLLRI X R 59iBida 9 HSS pent BIBL JV 1 SSL IRH ERI RRA AA 1 ATE E i E HIRR REE H HENTOR I e ZGHSIOL G SK E TTT Sergey BB l i ZSRAR tg tiia w f Estima tI E fT en 5 2AA gE EGE FEDER EL me AJ DARE BEER oa i23 X 25 SERERE PE ES Ti A EOIS BUER BOISSO THE EUN dci 255755 EM SPLEOBER RID ODB IMIBIIEIS IIU Si my es St l Boi esea RG DERI I ET 5 SE ee CZZ EAK a dE EE paeis Sipes isni gE Tasa E E Figure 11 9 Typical JJC transmission For those who deal with DX radio reception on the HF While listening to the interesting DX will be rewarded by received image Complete list of stations sorted by country or frequency see chapter 12 The detail list of frequencies and station schedule can be find in publication
149. picture quality is distorted The frequency of AFSK signal transmitted throught FM channel doesn t change so the color distortion known from SSB transmission doesn t appear The antenna of my station for Mir monitoring was 3 element yagi with vertical polarization normally used for ground repeaters I directed it to azimuth where Mir was nearest to my site Later I tried to direct rotator during orbit the azimuth and time I had computed and it was possible also to direct yagi by signal strength displayed on transceiver S metr 8 6 2 SuitSat In early 2006 originally planned to release about 3 months earlier were from the International Space Station ISS launched the satellite in an unusual project A RISS Amateur Radio on the International Space Station The satellite was named Suit Sat the code name is the AMSAT OSCAR 54 AO 54 And its name describes the full implementation of the satellite because on board equipment was built into expired Russian space suit type Orlan The transnsceiver Kenwood TH K2 was tuned to frequency 145 990 MHz and its power source was realized from the batteries so its lifetime was limited to a few weeks The satellite was programmed to broadcast a voice message prepared SSTV image in Robot 36 Color and telemetry data that contained information such as mea sured temperature and radiation The entire broadcast session lasts approximately 9 minutes After few hours after SuitSat s release ham radi
150. plementation of Scottie has this difference too The Scottie system also has four conventional modes and a special one described later Two with 256 lines per frame and two with 128 lines The difference in timing is not the same as in the Martin where the line speed of the faster mode is exactly twice the speed of the slower mode so the speed of the faster mode is lower than twice that of the slower mode 38 FORMATS OF SLOW SCAN TV TRANSMISSION 4 Image quality in the Scottie and Martin modes is the same Theoretically a slightly better quality can be achieved in Martin M1 than in Scottie S1 due to longer transmission but the difference is imperceptible The Scottie S1 and S2 are quite popular for North American stations and can often be heard on high frequency bands 4 2 4 1 Scottie DX special mode for long distance transfers This mode of the Scottie family achieves the best possible results in the transmission of slow scan television images There is one simple reason for this the transmission takes about 2 5 times longer than Scottie S1 There is an extended duration of the scan line but the duration of sync and gaps between color components remained the same This improvement is best seen on the receiving side The longer transmission time supports better image quality The improvement relies on the fact that each pixel can be read more times during signal sampling and that the loss of a few samples does not affect ov
151. plications during eighties e g transfer of radiologic pictures over phone lines and over satellite narrow band communication channels Often repeated mistake is that NASA has used the same system as amateurs for the SSTV transmissions from space in Apollo mission and that the first images from the Moon were transmitted in same way as amateur slow scan TV An NASA system for video transmission is different but their engineers also named it slow scan TV but it transmitted images at rate 10 frames per second with 320 lines The conversion to a normal television broadcast was made by optical path the television camera panned SSTV monitor for broadcast to millions of households The Amateur SSTV fly to space later when SSTV images were sent from space shuttle in SAREX missions or from orbital stations Mir and ISS These broadcasts were received by many hams over the World 83 8 HAM RADIO IMAGE OPERATIONS 8 3 Diplomas and QSL cards A tangible confirmation of ham radio contact is a QSL card although after finished QSO you may have few saved pictures on your hard drive as a memory of the contact But QSL cards still remains as traditional contact confirmation Also list of confirmed QSOs those you ve obtained QSL cards must be also accompanied for obtaining a number of ham radio diplomas So the picture of QSL has not same value as real QSL card In addition to diplomas issued directly only for SSTV contacts the diplomas like WAS WA
152. r 6 3 2 Scanning devices 6 4 Early FSTV SSTV converters 65 SUPERSCAN 2001 6 6 Tasco TSC 70P 6 7 Interactive Visual Communicator VC H1 T Computer operations zd Hardware configuration 7 2 Sound card as a modem Tol Sound processing in PCs 21 1 Sampling T22 Analog to digital conversion 1 2 8 Interface between TRX and PC d PTT control 12 Eliminate supply noise 7 3 Timing oscillator configuration Tabl Transmit timing offset 7 4 SSTV tuning 7 5 Video digitalization 1 6 Software for Windows 16 1 List of programs 50 11 SSTV software 70 12 Digital mode software with SSTV support rod Software for dedicated interfaces 46 AT AT 48 50 53 57 57 57 58 58 60 61 62 64 65 66 66 67 67 67 68 70 72 72 73 75 76 76 77 TT TT 78 78 8 Ham radio image operations 8 1 The reporting system 8 2 SSTV not only for hams 8 3 Diplomas and QSL cards 8 8 1 IVCA DX Achievement Award DXAA 8 9 2 DANISH DX SSTV AWARD 880 Russian SSTV Award 8 4 Contests 8 4 1 DARC SSTV Contest 8 4 2 Russian SSTV Contest 8 4 3 NVCG SSTV Contest 8 4 4 Danish SSTV Contest 8 4 5 JASTA SSTV Activity 8 4 6 Ukrainian SSTV Contest 8 5 SSTV repeaters 5 5 1 HF and 50 MHz repeater list 8 6 Ham radio satellites and space broadcast 8 6 1 SSTV from Mir station 8 6 2 SuitSat 8 6 3 Amateur Radio on the International Space Station 9 Introduction to digital slow scan TV 9 1 Digital communication basics 02 Error
153. r Amateur Radio Experiment 3 Shuttle Amateur Radio Experiment Amateur Radio on the International Space Station 35 4 FORMATS OF SLOW SCAN TV TRANSMISSION Mode Transfer Resolution Color Compatible name time format B amp W mode Robot 12 Color 12s 160x120 4 2 0 Robot B amp W 8 Robot 24 Color 24s 320x120 4 2 2 Robot B amp W 12 Robot 36 Color 36s 320x240 4 2 0 Robot B amp W 24 Robot 72 Color 728 320x240 4 2 2 Robot B amp W 36 Mode Color Sync pulses of Scan line Speed name sequence line color color Y R Y B Y lpm Robot 12 Color YCrCb 7 0 3 0 60 30 600 0 Robot 24 Color YCrCb 120 6 0 6 0 88 44 44 300 0 Robot 36 Color YCrCb 10 5 4 5 90 45 400 0 Robot 72 Color YCrCb 12 0 6 0 6 0 138 69 69 200 0 Table 4 3 The Robot parameters and scan line timing The first change was that instead of three separate syncs before each color com ponent there is just a single sync sent before each scan line The horizontal sync lasts 4 862ms After the horizontal sync the green component is sent then blue and last is the red component Between each color components there are short gaps of 1500 Hz lasting 0 572 ms Just like in the SC 1 the sequence green blue red was chosen Regardless of the order in which components are sent the image qual ity will not change But it is important that the receiv
154. racteristic that distinguishes it from other conventional modes Image transfer is achieved when the transmission time for the green component is equal to the sum of the transmission time of the red and blue components i e the ratio 2 4 2 of R G B components Between color components short gaps are not sent As we already know that the human eye is most sensitive to green by more than 50 The remaining 50 96 in SC 2 is split evenly between the red and blue compo nents Red and blue components are not processed for a differential signal This color reduction is not visible on common pictures but it may happen that some images e g B amp W mosaic may lose color information The system is less precise for color interpretation in comparison with Y CrCb modes but better in tuning re sistance One disadvantage of color reduction is found when green shadows appears on the image in stations without precise clock timing This mode is preferable in comparison to YCrCb because bad tuning will only reduce the contrast or saturation but the hue is not distorted Occasional green shadows remain as a tax for reduced transmission time The Wraase SC 2 family just like all other systems also has four different modes The SC 2 180 offers best quality for three minute transmission and unlike the pre vious modes does not use the RGB ratio 2 4 2 and is therefore a faster alternative to the Scottie DX mode The two minute SC 2120 uses the RGB format 2 4 2 Th
155. repeaters works also as beacon and sends periodically random images with identification and timestamp 8 5 1 HF and 50 MHz repeater list 8 6 Ham radio satellites and space broadcast For SSTV operations can be used a linear relay installed on some of the amateur radio satellites Amateur satellites orbiting the Earth for elliptical orbits Linear 87 8 HAM RADIO IMAGE OPERATIONS Freq Call QTH Activation Power Note 3 720 F5ZFJ Haute Sa ne JN27UR image linked with repeater on 144 525 MHz 14 236 VK3DNH Rochester Active 24 hours 14 239 VK2ISP Coogee New South Aktive 24 hours Wales 21 349 VKGET Brackenridge approx 50 100 W QRV 22 00 08 00 UTC 20km north from Brisbane 28 660 GI4GTY Lisburn image 28 688 HB9AC Eighental Lucerne 1750 Hz Linked with repeater on JN47CA 144 825 MHz FM 28 690 K3ASI North Carolina 1750 Hz 45W Aktive 24 hours beacon every 15 20 minut 28 700 ON4VRB Heist o d Berg 1750 Hz Linked with repeater on 433 925 MHz 28 750 ONODTG Doornik 28 900 EASEE 50 500 FGIKY Haute Savois 700 m USB 50 510 OZ6STV Copenhagen JO65ER 1750 Hz 60W Beacon every 30 minutes Table 8 4 none relays transponder performs retransmission of the wider frequency range typically 50 to 250 kHz So the satellite then transmits all the signals CW SSB received on the band not like the FM ground FM repeater to allow
156. requency RBW41 7 908 8 kHz 90 120 576 19 00 06 00 RBW48 10 130 0 kHz 90 120 576 06 00 19 00 Broadcast time 07 00 08 00 14 00 14 30 18 50 20 00 12 1 6 Northwood The United Kingdom Ident Frequency lpm IOC Power Note GYA 2 618 5 kHz 120 576 10 kW 20 00 06 00 GYA 4 610 0 kHz 120 576 10 kW GYA 8 040 0 kHz 120 576 10 kW GYA 11 086 5 kHz 120 576 10 kW 06 00 20 00 Broadcast time continuous at least on two frequencies 148 LIST OF PROFESSIONAL STATIONS 12 12 2 Africa 12 2 1 Cape Naval South Africa Ident Frequency lpm IOC Power Note ZSJ 4 014 0 kHz 120 576 10 kW pouze od 16 h do 06h ZSJ 7 508 0 kHz 120 576 10 kW ZSJ 13 538 0 kHz 120 576 10 kW ZSJ 18 238 0 kHz 120 576 10 kW pouze od 06 h do 16h Broadcast time 04 30 11 00 15 30 17 00 22 30 12 3 Asia 12 3 1 Beijing China Ident Frequency lpm IOC Power Note BAF6 5 526 9 kHz 120 576 6 8 kW BAF36 8 121 9 kHz 120 576 6 8 kW BAF4 10 116 9 kHz 120 576 10 kW BAF8 14 366 9 kHz 120 576 15 kW BAF9 16 025 9 kHz 120 576 kW BAF33 18 236 9 kHz 120 576 6 8 kW Broadcast time 00 08 11 58 13 40 19 04 22 40 12 3 2 Beijing China Ident Frequency lpm IOC Power Note 3SD 8 461 9 kHz 120 576 10 kW 3SD 12 831 9 kHz 120 576 10 kW 3SD 16 903 9 kHz 120 576 30 kW Broadcast time 07 55 11 30 149 12 LIST OF PROFESSIONAL STATIONS 12 3 3 Shanghai China Ident Frequency Ipm IOC Power Note BDF 3 241 0 kHz 120 576 BDF 5 100 0 kHz 120 576 BDF
157. requency free for SSTV and again listen if the frequency is really free There is unpleasant feature of some bands e g 20 meters 14 MHz that closer stations we can t detect although only a noise sounds from speakers doesn t mean that no connection is make on the frequency There are centre of activities recommended on all bands so for stations we should look around these frequencies They are also can be used as calling frequency and after the station calling CQ on the frequency makes contact the both station should tune to another free frequency QSY within the SSB segment Unfortunately reality does not comply with this so situation on very crowded band 20 meters is such that stations are glued to each other around 14 230 kHz they are interfering each other and weaker long distance stations are noised by undisciplined nearer stations If you find that there is activity tune to another frequency at least 3 kHz Good practice is chose frequency near centra of activity in 3kHz steps e g on 15 meters 21 334 21 337 21 340 21 343 21 346 There is great probability to find stations calling CQ or your own CQ will be heard by the other side You can call CQ by sending the image in the desired SSTV mode The image must contain code CQ It is good practice to place CQ test to the bottom of a picture so a station that tunes to the frequency later finds what is going on If you call CQ on calling frequencu add code QSY Change to transmis
158. rnia USA Hawai USA Massachusetts USA Halifax Canada Alaska USA Playa Ancha Chile Hawai USA Hawai USA Tokyo Japan Taipei China Lousiana USA California USA California USA Massachusetts USA Playa Ancha Chile Ident Frequencies kHz Note KVM 0 9982 5 11090 16135 East pacific GOES IR KVM70 9982 5 11090 16135 SW pacific GOES IR CFH 122 5 4271 6496 4 10536 13510 IR JMHx 3622 5 7795 13988 5 MTSAT BMF 4616 8140 13900 18560 GMS NMC 8682 12786 17151 2 22527 NE GOES IR NMC 8682 12786 17151 2 22527 Pacific GOES IR NMG 4317 9 8503 9 12789 9 17146 4 Tropical GOES IR NMF 4235 6340 5 9110 12750 NOJ 2054 4298 8459 12412 5 GOES IR KVM70 9982 5 11090 16135 East pacific GOES IR KVM70 9982 5 11090 16135 SW pacific GOES IR JMHx 3622 5 7795 13988 5 MTSAT BMF 4616 8140 13900 18560 GMS NMC 8682 12786 17151 2 22527 Tropical GOES IR NMG 4317 9 8503 9 12789 9 17146 4 Tropical GOES IR KVM70 9982 5 11090 16135 Pacific GOES IR NMC 8682 12786 17151 2 22527 Pacific GOES IR KVM 0 9982 5 11090 16135 Tropical GOES IR NMF 4235 6340 5 9110 12750 CFH 122 5 4271 6496 4 10536 13510 IR NOJ 2054 4298 8459 12412 5 GOES IR CBV 4228 8677 17146 4 KVM70 9982 5 11090 16135 East pacific GOES IR KVM70 9982 5 11090 16135 SW pacific GOES IR JMHx 3622 5 7795 13988 5 MTSAT BMF 4616 8140 13900 18560 GMS NMG 4317 9 8503 9 12789 9 17146 4 Tropical GOES IR NMC 86
159. rnia USA 120 576 01 40 16 08 4 416 0 VCO Sydney Nova Scotia Kanada 120 576 11 21 11 42 17 41 4 481 0 SVJ4 Athens Greece 120 576 08 45 10 44 4 610 0 GYA Northwood The United Kingdom 120 576 4 616 0 BMF Taipei China 120 576 4771 5 IMB51 Roma Italy 120 576 5 008 0 Moscow Russia 90 120 576 IOC 288 5 100 0 BDF Shanghai China 120 576 5 100 0 VMC Charleville Australia 120 576 5 250 0 BMF Taipei China 120 576 5 526 9 BAF6 Beijing China 120 576 157 12 LIST OF PROFESSIONAL STATIONS Freq Ident Station lpm IOC Note kHz Call sign 5 755 0 VMW Wiluna Australia 120 576 11 00 21 00 5 807 0 ZKLF Wellington New Zealand 120 576 5 857 5 HLL2 Seoul Republic of Korea 120 576 6 340 5 NMF Boston Massachusetts USA 120 576 6 496 4 CFH Halifax Nova Scotia Canada 120 576 6 834 0 GYA Northwood Persian Gulf Base 120 576 18 00 08 00 6 915 0 VCO Sydney Nova Scotia Kanada 120 576 22 00 23 31 6 987 0 Moscow Russia 90 120 576 IOC 288 7 305 0 JMH2 Tokyo Japan 120 576 7 396 8 HSW64 Bangkok Thailand 120 576 7 420 0 BDF Shanghai China 120 576 7 433 5 HLL3 Seoul Republic of Korea 120 576 7 535 0 VMW Wiluna Australia 120 576 7 695 0 Moscow Russia 90 120 576 IOC 288 7 710 0 VFF Iqaluit NWT Canada 120 576 00 10 09 00 7 710 0 VFR Resolute NWT Canada 120 576 21 00 23 30 7 880 0 DDK3 Hamburg Pinnenberg Germany 120 576 8
160. rogrammers can implement it to several computer platforms So thanks to open source idea there is few programs where is the RDFT mode available 116 DSSTV TRANSMISSION SYSTEMS 10 RDFT presentation in Dayton conference http replay web archive org 20080528090630 http www svs net wyman examples hdsstv 10 2 HamDRM system Communication system HamDRM is derived from open standard Digital Radio Mon diale 12 which was created for digitalization of radio broadcast on medium wave and short wave bands Normal DRM use bandwidth 4 5 kHz to 20 kHz for sound quality similar to FM broadcast on VHF The hamradio version HamDRM was cre ated by Francesco Lanza HB9TLK It is modified for usage in SSB channel with 2 5 kHz bandwidth HamDRM can be used for image and data file transfer and also for voice communication so it should be competitor for analog SSB in future The used modulation is COFDM Coded Orthogonal Frequency Division Multi plex which has maximal utilization of communication channel The Reed Solomon code is used for error correction 10 20 30 a W ul kli WA LU luj PTY m T Imi mm Mi bil JU 60 AMT i 50 Amplitude dB j 70 80 0 500 1000 1500 2000 2500 3000 Frequency f Hz Figure 10 7 The frequency spectrum of HamDRM system The OFDM signal consists of a huge number of subcarriers in baseband There are from 29 to 57 subcarr
161. rom Saturday 00 00 UTC to Sunday 24 00 UTC Bands 80 40 20 15 10 6 2m Score 2 points for every DXCC country 1 point for contact and bonus 1 point for contact with Danish station It is possible to make QSO with same station on different band The stations on 15 to 5th place will receive certificates Mail logs to Carl Emkjer Soborghus Park 8 DK 2860 Soborg Denmark 8 4 5 JASTA SSTV Activity Takes place in August from 1 00 00 UTC to 315 24 00 UTC on 3 5MHz band and all upper bands There are two categories J Japanese stations S all stations operating outside of Japan Exchange the usual RSV and number of QSO starting with 001 Regardless of bands used a station may only be contacted only once each UTC day The points for QSOs depend on band 1 point 3 5 28 MHz 2 points 50 430 MHz and 3 point for 1200 MHz and upper bands Multipliers are districts JA1 to JAO DXCC countries and working days max 10 Prefixes 7K to 7N are all JA1 districts Contest manager Yoshikazu Tanabe JA3WZT 1 905 8 Shimotaniganuki IRUMA SAITAMA 358 Japan send logs in TXT format to ja3wztOmue biglobe ne jp 86 HAM RADIO IMAGE OPERATIONS 8 http homepage3 nifty com jasta 8 4 6 Ukrainian SSTV Contest Takes place in first Saturday in December from 12 00 UTC to Sunday 12 00 UTC Bands 80 40 20 15 and 10m There are contest categories A One operator B One operator one band C Multiple operators F listeners T
162. rror detection and correction The error detection codes are used as a check of error free transmission The idea is based on some extra data redundancy added to a message The redundancy is generated from some input data on a transmission side FEC Forward Error Correction and on a reception side it is possible to check if the data was trans ferred without error An used code may have also ability for an error correction 96 INTRODUCTION TO DIGITAL SLOW SCAN TV 9 so data affected during transmission can be repaired on reception side without re transmission There are several error detection codes e g even parity described in chapter 3 6 2 The codes have several parameters First is the bit length of information k which we want to encode and the length of codeword n The difference r n k is the length of redundancy data Redundancy does not transfer any information but it is only used for error detection and possibly correction The ratio of the number of information symbols to the number of all symbols k n r jl TL TL expresses information ratio In practice we require that redundancy is minimized The ability of the code how many errors should be detected or corrected is given by Hamming distance It is determined as the number of different symbols of two different codewords The most important is minimal Hamming distance d of all arbitrary codewords E g Hamming distance of 0101000 and 0111001 is d 2 T
163. rrying frequency 1800 Hz Modulation by frequency deviation Value of central frequency 1900 Hz gt Value of frequency for black 1500 Hz gt Value of frequency for white 2300 Hz The frequency for black and white should not vary by over 8 Hz over a period of 30 s and by more than 16 Hz over a period of 15 minutes Levels of signals in case of AM receiving equipment should accept any level between 4 5 dB and 20 db zero reference level corresponding to a power of one milliwatt dissipated in a resistence of 600 ohms Contrast ratio contrast ratio for picture signals and control signals will be the same for any transmission and will be between 12 and 25 dB Facsimile transmission op meteorological charts over radio circuits gt When frequency modulation of the sub carrier is employed for the facsimile transmission of meteorological charts over radio circuits the following char acteristics should be used gt Centre frequency 1900 Hz gt Frequency corresponding to black 1500 Hz gt Frequency corresponding to white 2300 Hz gt When direct frequency modulation FSK is employed for the facsimile trans mission of meteorological ctorts over radio circuits the following character istics apply Decametric waves 3 MHz 30 MHz Centre frequency fo Frequency corresponding to black fy 400 Hz 145 11 FACSIMILE RADIOFAX gt Frequency corresponding to white fg 400 Hz
164. rst field This allows you to compensate if there is a significant multi path delay in regard to the two fields In ATV implementations the system can work well without this interactive tools But in practice especially on shortwaves where conditions change quickly the sec ond field could be phase shifted and this causes the notable toothy edge of the picture The QRM option can be combined with the narrow band mode Mode Transfer Color Scan line ms Speed Resolution name time sequence Sync R G B Ipm AVT 24 3ls 128x120 R G B 62 5 62 5 62 5 960 000 AVT 90 98s 256x240 R G B 125 0 125 0 125 0 480 000 AVT 94 102s 320x200 R G B 156 25 156 25 156 25 384 000 AVT 188 196s 320x400 R G B 156 25 156 25 156 25 384 000 AVT125BW 133s 320x400 Y 312 5 192 000 Table 4 6 The AVT scan line timing 42 FORMATS OF SLOW SCAN TV TRANSMISSION 4 4 2 6 Wraase SC 2 A later version of Wraase modes was first built in the newer converter SC 2 from Wraase Electronics Again it provides another variant of line sequential systems The author dropped the sequence of colors used in the earlier SC 1 converter so the colors are now sent in the order red green blue Additionally there is only one horizontal sync at the beginning of each line just as in the Scottie and Martin Unlike other systems the RGB system in the SC 2 has one cha
165. s carrying information are two 2200 Hz for mark log 1 and 1200 Hz for space log 0 We know v 1200 bps m 2 so symbol rate is equal to bit rate v 1200 Bd 1 200 Bd log m log 2 Um A packet radio is based on ITU T V 23 specification for telephone modems where bandwidth is limited to about 4kHz Modern dial up modems but have a much higher bit rates up to 56kbps and the bandwidth remains 4kHz How is that possible It s possible through the used advanced modulation which has more modulation states m then two For example modems based on V 32 specification can use bit rate up to 9 600 bps There is used QAM Quadrature Amplitude Modulation which in case of QAM 16 has 16 states per one modulation symbol The symbol rate in this case is v 9600 Bd 2 400 Bd log m log 16 Um One could think that it s possible to reach any speed because of improved modu lation and more states Unfortunately not because there are stark physical limits Maximal channel capacity C bit rate in bps is given by Shannon s law which de pends on bandwidth B Hz and channel parameters signal noise ratio S N dB S C B log 2 As we can see the maximum bit rate speed is not affected by the used technology but the bandwidth B and signal noise ratio SNR which cannot be changed SNR is given in decibels dB and describes the ratio of a signal power to a noise power of a processed bandwidth 9 2 E
166. s a mode of communication designed for image transfer Because SSTV is a narrowband mode it can be transmitted via voice channels with a standard SSB transceiver on all radio amateur frequency bands World wide communication is also possible during good conditions on high frequency bands 2 1 The beginnings In 1957 a student at the University of Kentucky Copthorne Cop Macdonalds WA2BCW now VY2CM found an article about a device developed by Bell lab oratories for image transmission via telephone lines The communication system fascinated the ham radio enthusiast because it needed a bandwidth as narrow as that of voice broadcast and could be transfered by regular ham radio transmitters Another image mode the radio fax facsimile was available then but it required a long duration about 20 minutes for a high resolution image transfer Such a duration length could not provide an impression of time consistency during a QSO and it also needed an intricate mechanical printer and electrosensitive paper It was necessary to invent something else There was an idea to transfer images coded into audio signals and display them on long persistence displays CRTs used in radars or slow scan oscilloscopes Then Copthorne started to work on how to transfer images via radio waves with a common ham radio transceiver Within six months he carried out many experiments with amplitude and frequency modulation and it resulted in the design of slow scan tele
167. s during QSO and then you will stunned by counterpart replay images 7 4 SSTV tuning First of all we need to find SSTV stations by listening near calling frequencies Thanks to typical SSTV sound and clattering of syncs it is not a problem to distin guish between SSTV and other communication modes Every SSTV program is equipped with precise tuning indicators spectroscopes see fig 7 11 The spectroscope shows frequency band from 1000 Hz to 2500 Hz with marks for critical frequncies 1200 Hz for syncs 1500 Hz and 2300 Hz for the video signal Is is possible to simple detect band of video signal and syncs during clear reception Rotate the tuning knob to achieve that all important frequencies are aligned in spectroscope display 7 5 Video digitalization The video digitizer should be additional equipment of SSTV station The device can convert output signal from camera into computer form There is a great choice 76 COMPUTER OPERATIONS 7 BE W See MMSSTV JVComm32 MSCAN QSSTV MixW Figure 7 11 Spectroscopes in common SSTV programs of many different devices with varying capabilities parameters and price You can choose some webcams frame grabbers TV cards or digital cameras Then your broadcast will not be limited only to pre prepared images and you will have a lot more fun with live transmission The cheapest option are web cameras they are equipped with a low resolution CCD and low cost optics but prov
168. s of mode formats described in detail 4 2 1 Wraase SC 1 This line sequential system was first among newly developed SFC systems Wraase SC 1 comes from the workshop of famous SSTV engineer Volker Wraase DL2RZ The system was most likely created by modifying existing equipment to operate in 8s mode or for frame sequential transmission Each scan line begins with 6 0ms sync then a green component follows and then the blue and red components A separate sync of 6 0 ms length precedes each colour component Wraase SC 1 has a major deficiency If the receiver loses sync during interference then the display system loses the ability to synchronize colors Because all lines are sent in the same way the color components cannot be recognized and the probability that the system reverts back to correct color sync is equal to one third In practice the system works but when the noise level is too high the received image contains few color bands as the converter loses and restores synchronization For this reason an additional sync pulse was added to subsequent productions of the SC 1 converter It consists of a truncated 5ms sync before the red line which is immediately followed by a short pulse of 2300 Hz frequency lasting 1 2 ms It allows the converter to regain synchronization after the noise subsides Additional synchronization occurs as a thin red stripe in the left edge of the image AII SC 1 modes have an image aspect ratio of 1 1 The original S
169. sed error detection and correction codes 97 9 INTRODUCTION TO DIGITAL SLOW SCAN TV Information Parity Codeword word 00 0 000 01 1 011 10 1 101 11 0 110 Table 9 1 none 000 001 010 011 100 101 110 111 Table 9 2 none 9 2 1 Cyclic redundancy check The CRC is commonly used code The systematic cyclic code adds a fixed length check checksum value to message The checksum is used for error detection CRC calculation is performed on block or section of data is stored in memory the k bit sequence is represented as a polynomial G x This is polynomial is divided by generating polynomial P x in arithmetic modulo 2 The result is polynomial Q x and the remainder after dividing R x The remainder R x is added to input data and transmitted in message On the reception side the division with P x is computed again and new remainder R x is compared with transferred remainder R x If both values are the same transfer went without error if not at least one bit was transferred incorrectly 9 2 2 Hamming code In the area of data communications e g TV teletext is sometimes used Hamming code which can detect up to two errors and in the case of a one error it is able to determine at what point of codeword error occurred and it can fix received bits Basically it uses for its purposes even parity While the parity bits are in the final codeword positioned at
170. sformed see schema in fig 9 3 In first step the image is divided on square block of 8 x 8 pixels and these 64 points is transformed from spatial domain z y to frequency i j by discrete cosine transform Just for completeness as follows 7 f l 2x l im 2y 1 jr DCT lL CT i j i E pixel x y cos 16 COS 16 l for a 0 where C a in other cases The first position 7 0 7 0 holds DC coefficient the mean value of the waveform for 64 values of block The other positions contains AC coefficients and their value is derived from deviations between each values and DC coefficient Basically the DCT trying the block of 8x8 to fit a linear combination of shapes given byt the previous formula Then follows a step that most affects the resulting image and a perception of the lossy compression level The quantization is carried out by individual members of a predefined luminance quantization table chrominance component has a different predefined table A member of the block at position 00 is divided by a member 00 104 INTRODUCTION TO DIGITAL SLOW SCAN TV origina image Macroblock Dekompozice Y 0 30R 0 59G 0 11B Cr 0 7R 0 33G 0 5B Cb 0 5R 0 42G 0 08B every pixel 128 IFHHHHII ius M AV rt EPIRI c i Tae DAT uf os sj ra oor fosfor ig sar so 7 9 108 106 97 93 106 94 94 ser fo ie Fs for os se s sls o aac sa Quan
171. sion on another frequency or on kHz and specify frequency where you can continue the QSO An answering to CQ call is possible in two ways The first one is that you answer by sending the image always in the same mode as called station Of course listen first that they are not another answering station Add the call signs e g OKIAAA de OK2BBB and report RSV into your picture The second method which is less used you can contact the station by voice and than send your image Beyond that it depends on your choice what style you will prefer when you make the SSTV connection It is possible to communicate only in SSTV when all infor mations are transmitted in pictures or use SSTV as addition for voice operations when both stations during QSO change few images First way prefers mainly Eu ropean stations but in northern America is preferred second one for making QSOs SSTV operation is closely linked with voice operation and although one picture can say thousand words it is sometimes more effective to use the microphone for 80 HAM RADIO IMAGE OPERATIONS 8 communication In particular if we enter into an ongoing QSO or calling party of more stations it is preferred to call firstly by voice before you send an image In earlier times operators before sending image said the mode they are use but now the SSTV software can automatically detect modes during transmission and the announcing mode is obsolete OK2MNM DEABISI Y 20
172. spectrum that will look like desired image The utility PicFall exe can be used for generating sound file from picture You can find it on website of DIGTRX author The input file is a bitmap in BMP format and output is WAV audio file Generate waterfall image by using PicFall exe http www qsl net py4zbz tutsstvi4 htm 128 DSSTV TRANSMISSION SYSTEMS 10 Spectrum Carrier Mh lu LN 7 ih W Jl jg WN U 0 500 1000 1500 2000 2500 3000 Fi ln Mi TL mm b Li UAI Figure 10 16 The principle of waterfall image display 129 11 Facsimile Radiofax Facsimile from latin facere make and simile similar is one of the oldest com munication modes and it is used for an image transmission The facsimile is mainly used by professional services for wireless distribution of meteorological maps and informations hence the name Weather Facsimile WEFA X follows from it The radiofax can be used by radio amateurs too 11 1 The history of image transmission Already in 1843 a Scottish clockmaker Alexander Bain suggested that some images can be broadcast via electric lines when it is electrically scanned by rows and point by point That s the basic idea of image transmission Bain s example was soon followed by other entrepreneurs In 1847 an Englishman Frederick Collier Bakewell reeled an image in the transmitter and sheet of paper to cylinder in
173. ssy compression fits on nature images and photographs but when it is used on a computer generated graphics such as diagrams and charts the image distortion is more noticeable on sharp edges and color gradients even at low compress ratio see section 9 3 4 3 Many compression algorithms were developed for lossless compression A sim ple algorithm is for example Run Length Encoding RLE This algorithm stores repeated bytes as their value and number E g AB AB AB CD EF EF EF EF EF is stored as 03 AB 01 CD 05 EF so instead of 9 bytes should be only 6 stored Other types of algorithms are based on statistical methods Before or during the compression process the algorithm determines the relative representations of elements of the file and those repeated frequently are expressed as a short code word Such algorithm is the Huffman coding described above Also Morse code is one of those codes frequently recurring characters such as E A I have assigned shorter codes and the less frequent such as H J F longer codes 9 3 3 1 Portable Network Graphics The PNG is appropriate graphics format with lossless compression PNG was cre ated to replace the outdated GIF format PNG is not limited to a palette of 256 colors like GIF and allows to set a continuous level of transparency alpha chan nel compared to GIF which has the option to choose only two levels yes or no transparency If you want to save the
174. synchronous communication and the exact timing of corresponding stations This special feature is described in more detail in chapter 4 2 5 about color AVT modes There is also the FAX480 mode for high resolution transmission with 512x480 image resolution described further in chapter 4 3 1 Early B amp W modes Wraase and Robot need to be synchronized with both line and vertical synchronization The line speed describes the free run speed but in reality it can be deviated up to 5 Modern modes like FAX480 and AVT 125 BW need accurate precision of line speed because just a little deviation of values in tenths causes image slant and distortion 29 4 FORMATS OF SLOW SCAN TV TRANSMISSION Mode Resolution Aspect Sync Scan line Line speed ratio ms ms lpm 7 2s 50 Hz 120x120 1 1 5 0 55 0 1000 0 8s 60 Hz 120x120 1 1 5 0 60 0 900 0 Wraase SC 1 8 128X128 1 1 5 0 55 0 1000 0 Wraase SC 1 16 256x128 1 1 5 0 115 0 500 0 Wraase SC 1 16 Q 128x256 1 1 5 0 55 0 1000 0 Wraase SC 1 32 256 x 256 1 1 5 0 115 0 500 0 64s mode 256 x 256 1 1 5 0 115 0 250 0 Robot B amp W 8 160x120 4 3 10 0 56 0 900 0 Robot B amp W 12 160x120 4 3 7 0 93 0 600 0 Robot B amp W 24 320 x 240 4 3 12 0 93 0 300 0 Robot B amp W 36 320 x 240 4 3 12 0 138 0 200 0 AVT 125 320 x 400 4 3 312 5 192 000 FAX 480 512 x 480 1 1 5 12 262 144 224 497 SP 17 BW 128 X 256 4 3 5 0 62 0 895 520 Ta
175. t QSO During this first QSO you or your partner can reveal some problems like bad settings of synchronization rates or noise affecting your computer signal or another problem you cannot reveal yourself You can also contact your local SSTV party for help International Amateur Radio Union IARU recommends usage of amateur bands and recommends specified frequencies for voice digital and image operations Latest band plans dates of March 2009 For IL T U region I Europe Africa and Middle East and Northern Asia there are recommended frequencies 8 1in table Frequency Recommendation 3 735 kHz center of activity 7 165 kHz center of activity previously 7030 7 040 kHz 14 230 kHz center of activity 21 340 kHz center of activity 28 680 kHz center of activity 144 500 kHz calling frequency for SSTV 432 500 kHz narrowband SSTV 433 400 kHz SSTV FM AFSK Table 8 1 Band plan recommendations for image communication 79 8 HAM RADIO IMAGE OPERATIONS The usage of side band is same like for voice operations on bands below 10 MHz it is LSB and for above bands it is USB Before you start calling CQ make sure that chosen frequency and its neighborhood are free SSTV operations are recommended in same sections of bands as voice communication and other modes so it is very unpleasant to interference each other 5o before you start transmission ask on chosen frequency Is this f
176. t hi res images was facsimile see chapter 11 So the creator Ralph Taggart WB8DQT called it FAX480 but compared with classic facsimile there are not many similarities The synchronization of the FAX480 is derived from the reference frequency of 4 0 MHz and a time unit is 4MHz 2048 1953 125 Hz Vertical sync is resolved as follows In the first five seconds a rectangular frequency modulation of 244 Hz between the black 1500 Hz and white 2300 Hz levels is transmitted This creates the AP T signal The tone 1500 Hz is transmitted for 4 time units 4 x 1 1953 125 2 048 ms and 2300 Hz for 2 048 ms too This gives a frequency of an ATP tone also 244 Hz 1 2 048 2 048 244 Hz This sequence is then repeated exactly 1 220x Originally the system did not use the VIS code but the code 85 was later added Originally vertical sync is followed by a phasing interval of 20 white lines Each begins with 5 12 ms sync 1200 Hz 10 time units but this interval is omitted in some implementations Now it s time to transfer the image itself It is composed of 480 lines Each line begins unlike the facsimile with 1200Hz sync with a length of 5 12 ms and then continues a scan line with 512 pixels The duration of the scan line is 512 x 1 1953 125 262 144 ms According to the creator the horizontal resolution of 512 points was selected just because the FAX480 operating software had a control menu to the left of the screen 5 Automatic
177. th net p PWP hampal RDFT http www svs net wyman examples hdsstv RXAMADRM Linux http paOmbo nl ties public html hamradio rxamadrm index html SSTV PAL Multimode http f6baz free fr FTP SSTVPalPlus WinDRM http nisu com windrm 10 4 Making QSO Digital SSTV is not spread too far There are few station found sporadically on the 14MHz band But there is also working party of German stations on the 3 7MHz 126 DSSTV TRANSMISSION SYSTEMS 10 band around the frequency 3 733 kHz almost daily in the evening Stations use only HamDRM system Listening to their signals is a good opportunity to try DSSTV reception and get some practice with it also try to make contact After that you already know how there is used special modulation schematic and error correct ing coding it is important to see if it at all works and how Will be there SSTV digitalization boom Some opponents of digital video broadcast claim that in conditions where we can receive noisy but still usable analog T V signal the digital TV cannot be received at all And same argument can say opponents of digital SSTV When there are good conditions it is possible only to tune on channel images are received automatically and operator should not do anything When interference gets stronger and signal weaker there can help more data instances or bad segment report and additional repetition of bad segments But when we only guess HamDRM signal drowned
178. the colours are the same They will be charac terized by the same gray level depending on their intensity Due to this fact a valid gray scale image Y created from basic colour components R G and B red green and blue is defined as Y 0 30R 0 59G 0 11B Note that the biggest factor 0 59 is just for the green so nearly 60 of colours that we can see depends on the green component and only 40 96 is of the remaining colour components This is used for simplicity in colour scan converters for BW images In past years BW images were not transmitted as true grayscale images but the brightness signal was derived from the green component of the image The difference in brightness between a true BW image and the green component of the same image is insignificant in most cases 19 3 MODERN SSTV FEATURES name name name sstv obr slozky ara r jpg sstv obr slozky ara g jpg sstv obr slozky ara b jpg file Krise file sstv obr slozky ara r jpg sstv obr slozky ara g jpg sstv obr slozky ara b jpg state unknown state unknown state unknown Red component Green component Blue compoment name name name sstv obr slozky ara rgb jpg sstv obr slozky ara gray jpg sstv obr slozky ara y jpg file Hose file sstv obr slozky ara rgb jpg sstv obr slozky ara gray jpg sstv obr slozky ara y jpg state unknown state unknown state unknown True colour image True grayscale Intensity Figure
179. the serial number is equal to the square of 2 1 2 4 8 Under the control bit position is then selected certain sequence of information words which is used to determine the value of control bit 98 INTRODUCTION TO DIGITAL SLOW SCAN TV 9 9 2 3 Reed Solomon code Hamming code works well in environments where errors occur randomly and their incidence is low e g in computer memory which can detect a erroneous bit to 100 million But even if that failure causes a greater number of adjacent bits are corrupted burst error the Hamming code is useless In the field of radio transmission where the signal is often affected by atmospheric disturbances fade outs and interference then errors occur in clusters This means that close to the incorrect symbol are other symbols incorrect too For burst error correction is applied Reed Solomon code RS RS codes are the most widely used codes for detection and error correction They are characterized by having the largest possible minimum distance and compared to the previous code will not correct the individual bits but all symbols RS code have found application in the number of areas is used by NASA for space com munications protects data on CD ROMs and DVDs and is also used for terrestrial transmission of HDTV or in the data modems for the cable television networks Like the CRC the RS code is systematic For its generation are used the algebraic calculations of Galois field
180. ther two modes allow the transfer of images in 256x240 resolution either in less quality for 36 seconds in a 4 2 0 format or in better quality in 4 2 2 format for 72 seconds Although the Robot modes were pushed away by modern synchronous modes that are more resistant to interference the 24s and 36s modes are faster than modes with RGB color coding and have better resolution than RGB modes with the same 34 FORMATS OF SLOW SCAN TV TRANSMISSION 4 i ce y j L gt S 1 TE iut 505low Scan TV A gt Rue d gt Eu low Scan TV Messlow Scan TV A Robot 36 Color Robot 72 Color Figure 4 4 Comparison of Robot color modes transmission time You can find their benefits on VHF with FM transmission because it eliminates the need for precise tuning Robot 36 Color was used in MAREX SAREX and ARISS programes for SSTV transmission from orbital stations Mir ISS and space shuttle missions It is a pretty good compromise between image quality and transfer time because space stations on low earth orbit can be received within just 10 minutes during their orbit 4 2 3 The Martin synchronous system The creator of this popular system is Martin Emmerson G3OQD He originally named it New Modes but to avoid confusion between other newly emerging SSTV modes the community universally named modes after their creators The Martin was created to overcome SFC problems in systems like SC 1 due to two main changes Mi
181. tio 29 1 Ratio 50 1 4 779 B 2 909 B Figure 9 7 File size depends on the compression ratio of JPEG 2000 The new JPEG2000 has also progressive mode like an old JPEG So the received image can be viewed during reception You can see phases of reception in fig 9 8 9 3 4 3 Lossy versus lossless image compression conclusion In JPEG section is described that lossy compression is not suitable for all types of images Charts diagrams and other images featuring sharp color gradients get significant loss see fig 9 6 Despite the significant quality loss the file size is not considerable reduced inTable tab comparison contains a comparison of file size for various formats As the input file was used smiling face from fig 9 6 stored at a resolution of 256 x 192 in 16 colors Even relatively dumb RLE algorithm for lossless compression but maintaining a 10096 quality beats JPEG It is the user s choice how to deal with the right choice of 109 9 INTRODUCTION TO DIGITAL SLOW SCAN TV format and select a suitable compromise between resolution number of colors and image quality 80 Figure 9 8 Progressive display of JPEG2000 image depends on amount of transfered data original image has 400 x 298 resolution 110 INTRODUCTION TO DIGITAL SLOW SCAN TV Format Quality File size Windows Bitmap 100 24 654 B JPEG 100 17 740B JPEG 15 1 300 B JPEG 50 96 5 298 B TIFF Pac
182. tive colour model is a method of transmission that take more time to transmit but it provides a transfer of true colours 3 5 2 Composite colour model The second type of colour transmission is called Y CrCb In fact it is a similar system as is used in colour fast scan television where each colour component R G and B are transformed to luminance and chrominance colour information signals Unlike RGB the transmission time of an image is shorter This colour coding is used for BW and colour compatibility in television broadcasts In which colour broadcasts can also be received by a BW television The image scan line contains colours transformed into two components lumi nance and chrominance The chrominance signal is composed of two differential colour signals RY and B Y Signal Y is called luminance and contains the signal 21 3 MODERN SSTV FEATURES f kHz Figure 3 8 Decomposition of colour image into YCrCb signals corresponding to brightness produced by the equation Y 0 30R 0 59G 0 10B The Y is for chrominance signals subtracted from the red and blue components On the receiving side the individual colour components are restored R R Y Y and B B Y Y We need a third green component the G which is derived from RY and B Y from the expression G Y 0 51 R Y 0 19 B Y Hereby we get complete colour signals 22 HG MODERN SSTV FEATURES 3 There are two formats
183. tization table The coefficients of quantization G Z en E E E 40 18 2 table here for 50 96 quality they can gt H 12 14 19 26 inli i Quantization 4 lt EE etl ee be multiplied by constant a which gives a lossy ratio 705 16 44 un 109 11 10 22 37 pm Quality Q alum 1 lt Q lt 50 a 50 Q 7 92 95 51 lt Q lt 100 a 2 Q 50 Linearization 44 10 8 5 10 4 1 2 o 401 M 1 1 0 0 0 0 0 1 O O O O O 1 0 O 44 1j j Run length encoding zeros categ value Image block is linear combination of patterns given by DCT 44 0 4 10 0 4 8 0 3 5 0 4 10 0 3 4 0 1 1 0121 2 Huffman coding 0 3 4 0 111 0 1 1 0 1 1 O 1 1 5 1 1 5 1 1 EOB only AC coefficients gt 10111100101101111000101011110010001100 10101 100 10000000000 100011110101 111101001010 bit stream Figure 9 3 The JPEG compression for one 8x8 block of brightness 105 9 INTRODUCTION TO DIGITAL SLOW SCAN TV of the quantization table and the position of the integer part of number is stored at position 00 continues 01 01 02 02 up to each value is divided by its corresponding coefficient The result of this process is a square matrix where most information is stored in the upper left corner and around the lower ri
184. transmitted during the passage of the dead sector should correspond to white but it is permitted that a black pulse be transmitted within and not exceeding one half length of the dead sector 8 Selection of index of co operation a five second transmission of alternating black and white signal at 300 Hz for index 576 675 Hz for index 288 The envelopes of the signals transmitted will be roughly rectangular 9 Synchronization the scanning speed should be maintained within 5 part in 109 of the normal value 10 Starting recorders recorders should be designed to start upon receipt of either the index selection signal or the phasing signal and no special signal for starting will be transmitted 11 Phasing 144 FACSIMILE RADIOFAX 11 12 13 14 15 16 17 a 30 second transmission of alternating white and black signal at the following frequencies gt 1 0 Hz for speed of 60 rpm gt 1 5 Hz for speed of 90 rpm gt 2 0 Hz for speed of 120rpm Adjustment of recording levels adjustment of recording level when used should be effected by reference to phasing signal Stopping recorders a 5 second transmission of alternating black and white signals at 450 Hz fol lowed by 10 seconds of signals corresponding to continuous black Modulation characteristics Amplitude Modulation The maximum amplitude of the carrying frequency should correspond to the transmission of signal black Value of the ca
185. ve both the vertical and horizontal scans The output voltage of these circuits is the saw tooth voltage and drives deflection plates of long persistent CRT limiter SSTV input image discriminator image amplifier sync separator sync amplifier sync rectifier horizontal scan vertical scan Figure 6 4 Block scheme of SSTV monitor After the separation of sync the image signal goes to the image intensifier and de tector After filtration the signal is fed to the cathode ray tube grids and modulates the electron beam Subsequently the image is displayed on the screen The disad vantage of this process is that the image is seen clearest during the reception and then the brightness fades To be able to view the image after the 8 seconds transfer a well darkened room was necessary 6 3 2 Scanning devices The image scanning methods used in early SSTV transmission can be classified into electronic and electro mechanical methods Purely electronic systems used cameras with a sensor element like vidicon plumbicon or other camera tubes In SSTV cameras the vertical scan frequency was adjusted from 50 Hz to 16 6 Hz ie horizontal scanning frequency for 7 28 SSTV or 15Hz for 60Hz standard Then a whole camera or just a deflection unit only was rotated 90 The TV camera 60 SSTV EQUIPMENT 6 scans the image line by line providing the sampling circuit with input The sampli
186. ve a few interesting fea tures which we are about to delve into 46 FORMATS OF SLOW SCAN TV TRANSMISSION 4 Mode Transfer Color Scan line ms Speed Resolution name time sequence Sync X 2 R YB Y Ipm L PD 50 50 s 320x240 Y C 20 0 91 520 91 520 91 520 309 150866 PD 90 90 s 320x240 Y C 20 0 170 240 170 240 170 240 170 687301 PD 120 126s 640x480 Y C 20 0 121 600 121 600 121 600 235 997483 PD 160 161s 512x384 Y C 20 0 195 854 195 854 195 854 149 176545 PD 180 187s 640x480 Y C 20 0 183 040 183 040 183 040 159 100552 PD 240 248 s 640x480 Y C 20 0 244 480 244 480 244 480 120 000000 PD 290 289s 800x600 Y C 20 0 228 800 228 800 228 800 128 030044 Table 4 9 The PD modes scan line timing 4 4 1 MSCAN TV The modes TV 1 and TV 2 were one of many experiments in the SSTV transmission field An interesting feature is the use of interlaced transmission They do not use the same half frame interlacing like normal television does But the whole image is divided into four quarter frames These frames are transmitted gradually in the direction from top to bottom so you can get a first preview of the image after the first quarter of transmission time but only in low resolution Thanks to interlacing the resolution increases gradually during transmission up to 320x256 It is possible to receive these modes wit
187. vision During the next six months he created an SSTV image scanner so practical experiments could be done on the ham bands The first television image crossed the Atlantic on the 20 of December 1959 During the next ten years Copthorne and a group of amateurs worked on SSTV improvements and they created the basic standard for SSTV and developed a sam pling camera Their work was completed in 1968 when the FCC Federal Communications Com mission formally authorized SSTV operations 2 SLOW SCAN TELEVISION The first image that crossed Copthorne the Atlantic received by Macdonald s broadcast John Plowman G3AST Figure 2 1 Early slow scan television images A few months later ham radio magazines published the first articles about the new communication mode It led to a huge interest by ham operators and a real SSTV boom 2 2 Image transmission The basic idea of SSTV is to transfer television images with the standard transceiver However a television broadcast requires a large bandwidth The reduction of the television signal is achieved by lowering of horizontal row and vertical image scans which must be reduced to a minimal frequency This means that a typical 3MHz signal of black and white television must be reduced to 3 kHz the reduction of bandwidth is around 1000 1 Nowadays the bandwidth reduction is bigger be cause color image needs approx 6 MHz Therefore only static images with lower resolution can
188. volume levels to use the tuning indicator to manually change the transmission mode to load and save images in common graphic formats to create an image gallery for transmission and to add text into transmitted images VVV VV VV 7 1 Hardware configuration Take your time in selecting a suitable configuration of the computer in your ham shack The unpleasant fact is that operating system and software requirements are constantly on the rise For SSTV operations it is possible to use obsolete PCs with old 386 processors The Hamcomm modem and some other popular programs from the nineties run on DOS In this case 4MB of RAM a hundred megabytes hard disk and SVGA graphics card with 256 colors are enough But graphic cards with 32 or 64 thousand colors are more suitable To use a sound card a good PC is needed At the least it should be configured with 150MHz Pentium 64 MB RAM and few gigabytes hard disk A graphics card needs to support 1024x768 resolution in 64 thousands or 16 7 million color mode 66 COMPUTER OPERATIONS 7 The minimal operating system is Windows 95 OSR 2 but some new programs may not run in Win95 I recommend having better hardware but you don t need the latest mega hyper model There are also software products for Mac OS X and for GNU Linux but the largest selection is for Microsoft Windows 7 2 Sound card as a modem A sound card is standard PC equipment these days It can be used as a music pla
189. y and the P3 runs fastest at three minutes with a horizontal resolution about half of a P7 A potential disadvantage of these modes is actually quite a long transfer time which makes it difficult to use on highly variable short waves For those who do not mind the long transmission times it can be used for exchanging pictures on VHF Mode Transfer Color Scan line ms Speed Resolution name time sequence Sync R G B lpm Pasokon P3 203s 320x496 R G B 5 208 133 333 133 333 133 333 146 56488550 Pasokon P5 305s 640x496 R G B 7 813 200 000 200 000 200 000 97 70992366 Pasokon P7 406s 640x496 R G B 10 417 266 667 266 667 266 667 73 28244275 Table 4 8 The Pasokon TV scan line timing 45 4 FORMATS OF SLOW SCAN TV TRANSMISSION 4 3 3 PD modes PD modes are the result of a cooperation between Paul Turner G4IJE and Don Rotier KOHEO The mode was first introduced in May 1996 and it was developed to improve image quality and especially to reduce transfer times in comparison with Pasokon TV For speeding up transmission YCrCb color coding is used in the 4 2 0 format If you divide the total time between two syncs by four the result is the actual time for each color component The scan line begins with 20 0ms sync then there is a 2 080 ms gap of black and the first luminance signal Y It is followed by chrominance signals R Y and B Y without a
190. yer for multimedia games and recording The main application of a sound card in hamshacks is as a MODEM The modem MOdulator DEModulator allows computer information to be transmitted and received over physical media like radio waves or telephone lines The modem translates analog signals to digital data and vice versa 7 2 1 Sound processing in PCs To allow the computer to work with sound signals the signal must be converted into a format suitable for data processing digital or discrete signal 7 2 1 1 Sampling The digital conversion process begins with sampling Sampling is an activity which periodically scans the current value of the analog signal For example this happens 11 025 times per second or depends on a user defined sample rate supported by the sound card The sampling frequency of sound cards ranges from 8 kHz suitable for internet telephony up to 96 kHz designated for more exacting requirements of recording studios OANW ROO t n n 100100010001011101110 analog to digital converter samples of analog signal analog input digital data Figure 7 1 The conversion of an analog signal into numeric data 67 7 COMPUTER OPERATIONS The answer to the question of what sampling frequency should be used gives us Shannon s theorem also knows as Nyquist Kot lnik Shannon theorem It defines that a signal continuous in time containing spectral components with the high est frequency f
191. ymbol numbers produced by the outer encoder are the input to the inner encoder The inner coding scheme uses RS 8 4 where is 50 redundancy All 8 symbols are used for phase settings for each of 8 subcarriers so the inner code block is transferred paralely The decoder of inner code on reception side is able to correct whole block if 6 of 8 symbols are transferred without error 112 DSSTV TRANSMISSION SYSTEMS 10 modulation angle subcarrier angle low pass filter subcarrier frequency T 590 820 1050 5 SIN 1280 1510 1740 SIN 1970 2200 Hz low pass 2 filter gt Figure 10 2 Block diagram of RDFT modulator for one subcarrier Operator can choose one of four modes in all cases the modulation speed is same 122 5 Bd but the level of error control differs Table 10 1 are parameters of RDFT modes You can choose lower error con trol level when band conditions are good or higher level in case of bad conditions and big interference The redundant data consume 70 96 of all transferred data for Wyman 14 so there is possible to apply an extensive error correction The Wyman 13 is recommended for long distance contacts and Wyman 12 for intracontinental QSOs Transferred data block consists of three parts The first is LEADER it uses always same modulation scheme and error cod ing It contains RDFT mode identification and it is used for detection of two parameter The first parameter is a tuning deviat
192. ystem upgrade is simply achieved by an EPROM upgrade Its last version 1 6 VVVVV VY V supports these modes gt Color modes gt Scottie S1 2 3 54 DX gt Wraase SC 1 24 48Q 48 96 D Robot Color 12 24 36 72 gt Wraase SC 2 30 60 120 180 gt AVT 24 90 94 188 plus QRM Narrow variants B amp W modes gt Robot 8 12 24 36 gt Wraase SC 1 8 16 16Q 32 gt AVT BW 125 gt Radio fax reception gt 60 90 120 240 lpm Contains four memory banks and stores images in a resolution 256x240 with 18bit color depth 262 144 colors TV PAL decoder with delay lines for perfect image digitization High speed parallel interface for computer connection RGB video output Control by computer mouse available firmware 1 3 Text addition Backup of CMOS memories for texts and configuration High stability oscillator for free run reception 63 6 SSTV EQUIPMENT 6 6 Tasco TSC 70P A modern type of converter is the TSC 70P TSC 70N works with NTSC norm This converter includes a DSP for better reception of weak signals It supports all conveniences such as the automatic detection of VIS code and free run reception _ TE 5 1 Telereoder ColorScanConverter M LJ Figure 6 7 Japan converter Tasco TSC 70P Supported modes Martin M1 M2 gt Scottie S1 S2 gt Robot Color 36 72 gt AVT 90 94 Narrow regime only in TSC 70N available Im

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