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1. Xi Combif XK A teh Sue t 4 t a A y 7 A d A f f gt Del lt f Felt i i i Figure 2 2 Sampling a Signal 2 2 1 Star Transform Taking the Laplace transform of this infinite sequence will yield us with a special result called the star transform which depends on the sampling time T and is different for a single signal depending on the speed at which the signal is sampled il LF Fie A sampler is usually denoted on a circuit diagram as being a switch that opens and closes at set intervals These intervals represent the sampling time T 2 2 2 Sampling Time This is the amount of time between successive samples Samplers work by reading in an analog waveform and catching the value of that waveform at a particular point in time This value is then fed into an ADC converter and a digital sequence is produced Figure 2 3 Sampling Time 2 2 3 Sampling Delays Real samplers take a certain amount of time to read the sample and convert it into a digital representation This delay can usually be modeled as a delay unit in series with the sampler 2 2 4 Sampling Jitter Samplers in real life don t always take a perfect sample exactly at time T but instead sample around the right time The difference between the ideal sampling time T and the actual sample time is known as the Sampling Jitter or simply the jitter 7 Theorem The sampling theorem states that if we convolute
2. 3 10 4 Testing Testing is done via a dummy load where dummy antenna is connected to the output of the transmitter and electrically simulates an antenna to allow the transmitter to be adjusted and tested without radiating waves In testing the audio a dummy load is connected to the output of the amplifier to electrically simulate a loudspeaker allowing the amplifier to be tested without producing sound 52 Figure 3 23 Dummy load model When testing audio amplifiers the loudspeaker is replaced with a dummy load so that the amplifier s handling of large power levels can be tested without actually producing intense sound The simplest is a resistor bank to simulate the voice coil s resistance dd RIMA Figure 3 24 Pie chart display of the signal content 53 3 10 5 Demodulation The original information bearing signal is extracted from a modulated carrier wave by use of a 3 set demodulator outputting a digital signal The signal is fed into a Phase Locked Loop and the error signal is used as the demodulated signal 3 10 6 Transmission The signal can then finally be transmitted to the users where the receiver end would decode the content to obtain the specific frequencies on use Two methods are used depending on the signal content and mode of airing a Microwave point to point b Satellite c Fibre optic For instance parliament sessions are aired via Fibre optic means while normal programs are propagated th
3. UNIVERSITY OF NAIROBI SCHOOL OF ENGINEERING DEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERING CONVERSION OF ANALOGUE TO DIGITAL TRANSMISSION CONVERTER PROJECT NUMBER 126 NAME KHAMIS LUQMAN NASSIR REG NO F17 36221 2010 SUPERVISOR PROF MAURICE MANGOLI EXAMINER PROF ODERO ABUNGU A project report submitted to the Department of Electrical and Information Engineering in partial fulfillment of the requirements of the degree of BSc Electrical and Electronic Engineering of the University of Nairobi DECLARATION OF ORIGINALITY NAME KHAMIS LUQMAN NASSIR REGISTRATION NUMBER F17 36221 2010 COLLEGE College Of Architecture and Engineering FACULTY Engineering DEPARTMENT Electrical and Information Engineering COURSE Bachelor of Science in Electrical and Electronic Engineering PROJECT NAME Conversion of Analogue to Digital Transmission Converter 1 understand what plagiarism is and am aware of the university policy in this regard Za declare that this final year project report is my original work and has not been submitted elsewhere for examination award of a degree or publication Where other people s work or my own work has been used this has properly been acknowledged and referenced in accordance with the University of Nairobi s requirements 3 have not sought or used the services of any professional agencies to produce this work 4 have not allowed and shall not allow anyone to copy my work with the in
4. Te e KE ainia 32 SEET Ae 32 SN METAL c 32 LS AE MAA EE 3 3 Processing Techniques in use in audio bhandltng conc conc nnnnnnnnnononnnos 32 EE 34 39 UPR EE 34 sO DOWNIN K serre ecesete tage ao cS che ecesite eee SS A ec et cacesueea dos dasa 35 3 7 Analogue FM Transmission Radio 36 e R A Me sacha A E A A E E hae niiciue E AE A A E A 38 iz Oia 39 E AAA O O 40 E 41 ASS E A A EE Ee 44 0 Gracel EH id aio as 45 39 Analogue Trans misson TV ita liste lili 46 3 10 Digital RTR E alo ot le dilo cdo 48 IAO F Excite EE en ST ii nN Ee ce ES 49 IA WI Ue Teast ets hes Steet se ae ale sets ea Maule hae eal sen ata enol soeten eta eee 49 DAD 3 Water COOMNE Siena re 51 RE PPP 0b ici saat d sasan acini sissiacings pa ick state ES 92 IOS Demo du lA id 54 FIO he ee EE 54 PORD Od 0 POPE OP O cert eee S 55 A AeA MalOO US trans MISSION E O ila raunaateaies 56 Az Dreital TRANS MISSO Mae als 57 AL Pros and CONS laa 57 EEEO IU SO Mastek A EEEE dias 60 xi 5 2 Recommendations xii CHAPTER 1 INTRODUCTION 1 1 Background to study Analog signals are continuous in both time and value Analog signals are used in many systems although the use of analog signals has declined with the advent of cheap digital signals All natural signals are Analog in nature Analog transmission is a transmission method of conveying voice data image signal or video information using a continuous signal which varies in amplitude phase or some other property
5. can be physically transmitted a process of varying one or more properties of a periodic waveform called the carrier signal with a modulating signal that typically contains information to be transmitted There are two principal motivating reasons for modulation Matching the transmission characteristics of the medium and considerations of power and antenna size which impact portability The second is the desire to multiplex or share a communication medium among many concurrently active users AMMAN AA AAA f A MANANANRANANA f iSi ivi TTT AN UUNUHNUUNUUNUUNHUN Aa A Sees A HA ani TT 944444 L TTT y y V U H H Wu al III KK Y Carrier Signa Hit ij Y IO J f 1 U Y Y Carrier ven Modulatne Sine Wave Signal J K HR Modulating Sin Wave Signal N E A AA j AAA H II A A fi V e 1 l i ft A It a 4 n LA ARS KA Hi TIVA H LALA A UU Il AN LU Vd d H N y VYY V T d J U d d d j VW lj U y Led vency Modulated Signal Amplitude ot sted Sign Figure 2 5 Modulation 12 The aim of digital modulation is to transfer a digital bit stream over an analog bandpass channel for example over the public switched telephone network where a bandpass filter limits the frequency range to 300 3400 Hz or over a limited radio frequency band The aim of analog modulation is to transfer an analog baseband or lowpass signal for example a
6. directly by analog components though some processes aren t available except in digital form The primary disadvantage of analog signaling is that any system has noise i e random unwanted variation As the signal is copied and re copied or transmitted over long distances these apparently random variations become dominant Electrically these losses can be diminished by shielding good connections and several cable types such as coaxial or twisted pair The effects of noise create signal loss and distortion This is impossible to recover since amplifying the signal to recover attenuated parts of the signal amplifies the noise distortion interference as well Even ifthe resolution of an analog signal is higher than a comparable digital signal the difference can be overshadowed by the noise in the signal 56 4 2 Digital Transmission Digital transmission was described as a method of storing processing and transmitting information through the use of distinct electronic or optical pulses that represent the binary digits O and 1 Digital transmission covered less area of broadcast in comparison to analog transmission due to the discrete nature Transmission Boosters were laid along the line to propagate the signal to greater lengths 4 2 1 Pros and cons Advantages of Digital Transmission e Less expensive e More reliable e Easy to manipulate e Flexible e Compatibility with other digital systems e Only digitized informati
7. here the phase shift of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal ARPAPLITUDE FPAODULATED SIGNAL ANTENNA Va S RADIO FREQUENCY SIGNAL la RF IMA MAD ALVA BUFFER iii iil POWER es 1 OSCILLATOR Ch AMPLIFIER HT AMPLIFIER i t SS AMPLIFIER a FREQUENCY SIGNAL MICROPHONE DC OLAGE POWER SUPPLY Figure 2 6 Amplitude Modulation 14 2 3 2 Frequency modulation FM This is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave Compare with amplitude modulation in which the amplitude of the carrier wave varies while the frequency remains constant 1 Modulation d errors t Frequency Modulation Lo En de ollo a be em ze mm mm mm a i 1 Phase 1 Modulation l i f y K dm r em Em n be dede dsd well Figure 2 7 Frequency Modulation In analog signal applications the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input signal amplitude Digital data can be encoded and transmitted via a carrier wave by shifting the carrier s frequency among a predefined set of frequencies a technique known as frequency shift keying FSK FSK is widely used in modems and fax modems and can also be used to send Morse code Radio teletype also uses FSK Frequency modulation is used in r
8. many samples we need to remove some through a process called Down Sampling In a down sampler certain samples are removed from the digital signal and the remainder of the samples may be altered to appear more spread out Down sampling is usually performed according to a fractional rule An example would be a 2 1 down sampler which removes every second sample to decrease the bitrate in half 2 2 15 Up Sampling If the sampler isn t producing samples fast enough we need to create more samples The process of creating more samples is called Up Sampling In the most basic up sampling scheme additional samples with a value of zero are added between the existing samples This method is called Zero Padding but other methods such as interpolation can also be used 2 2 16 Zero Padding Adding samples with a O value in between given samples to increase the bitrate 2 2 17 Interpolation Using some mathematical rule to create new samples a between two existing samples n and m where a f n m 10 2 2 18 Linear Interpolation In linear interpolation a straight line is drawn between the two samples on either side of the new sample The new sample value then is considered to be a point on this straight line or the average value This is called linear interpolation because the new samples will be on this line formed by the old samples As an example consider that we want to double the sample rate by inserting linearlyinterpolated samples
9. mode it is easy to see that the signal shape is dependent on the time or duration that the probe coil is sensing something 3 7 4 1 Filters Effects The two standard filters tuned are the High Pass Filter HPF and Low Pass Filter LPF or a combination high and low pass filter Band pass filter The HPF allows high frequencies to pass and filters out the low frequencies The HPF is basically filtering out changes in the signal that occur over a significant period of time 41 The LPF allows low frequency to pass and filters out the high frequency In other words all portions of the signal that change rapidly have a high slope are filtered such as electronic noise The gradual low frequency changes were first filtered out with a HPF and then high frequency electronic noise was filtered with a LPF to leave a clearly visible flaw indication Since flaw indication signals are comprised of multiple frequencies both filters have a tendency to reduce the indication signal strength Additionally scan speed must be controlled when using filters Scan over a flaw too slow and the HPF might filter out the flaw indication Scan over the flaw too fast and the LPF might eliminate the flaw indication 3 7 4 2 Filter Settings If the spectrum of the signal frequency and the signal amplitude or attenuation are plotted the filter responses can be illustrated in graphical form The LPF allows only the frequencies in yellow to pass and t
10. up the signal from one the two methods e Satellite dish e Downlink The 100 kW VHF transmitter is used which uses frequency modulation FM to provide high fidelity sound over broadcast radio 36 FM radio uses the electrical image of a sound source to modulate the frequency of a carrier wave At the receiver end in the detection process that image is stripped back off the carrier and turned back into sound by a loudspeaker When information is broadcast from the FM radio station the electrical image of the sound taken from a microphone or other program source is used to modulate the frequency of the carrier wave transmitted from the broadcast antenna of the radio station This is in contrast to AM radio where the signal is used to modulate the amplitude of the carrier The range of mono FM transmission is related to the transmitter s RF power the antenna gain and antenna height In Nairobi for instance the distance for coverage from transmission is approximately 80 Km consisting of sharp depressions along the line Figure 3 8 A typical FM transmitter control system 37 The stations for the above system at KBC transmitters include Kiswahili service 92 9 MHZ CORO FM 99 5 MHZ English service 95 6 MHZ Metro FM 101 9 MHZ CRI FM China 91 9 FM A A YS The frequency ranges are 88 0 MHz 108MHz yielding 20 MHz Bandwidth with the transmitter consisting of all frequency ranges due to harmonics Carrier wa
11. 0 Multiplexing A device that performs the multiplexing is called a multiplexer MUX and a device that performs the reverse process is called a demultiplexer DEMUX or DMX Inverse multiplexing IMUX has the opposite aim as multiplexing namely to break one data stream into several streams transfer them simultaneously over several communication channels and recreate the original data stream 2 5 1 Multiplexing Types Multiple variable bit rate digital bit streams may be transferred efficiently over a single fixed bandwidth channel by means of statistical multiplexing This is an asynchronous mode timedomain multiplexing which is a form of time division multiplexing Digital bit streams can be transferred over an analog channel by means of code division multiplexing techniques such as frequency hopping spread spectrum FHSS and directsequence spread spectrum DSSS In wireless communications multiplexing can also be accomplished through alternating polarization horizontal vertical or clockwise counterclockwise on each adjacent channel and satellite or through phased multi antenna array combined with a multiple input multipleoutput communications MIMO scheme 19 2 5 1 1 Space division multiplexing In wired communication space division multiplexing simply implies different point to point wires for different channels Examples include an analogue stereo audio cable with one pair of wires for the left channel and another for th
12. 1 OFDM Modulation The sequence of blocks is modulated according to the OFDM technique using 1705 or 6817 carriers 2k or 8k mode respectively Increasing the number of carriers does not modify the payload bit rate which remains constant 3 2 12 Interval insertion To decrease receiver complexity every OFDM block is extended copying in front of it its own end cyclic prefix The width of such guard interval can be 1 32 1 16 1 8 or 1 4 that of the original block length Cyclic prefix is required to operate single frequency networks where there may exist an ineliminable interference coming from several sites transmitting the same program on the same carrier frequency 3 2 13 DAC and front end The digital signal is transformed into an analogue signal with a digital to analogue converter DAC and then modulated to radio frequency VHF UHF by the RF front end The occupied bandwidth is designed to accommodate each single DVB T signal into 5 6 7 or 8 MHz wide channels The base band sample rate provided at the DAC input depends on the channel bandwidth 3 3 Processing Techniques in use in audio handling Audio unprocessed by reverb and delay is metaphorically referred to as dry while processed audio is referred to as wet e Echo to simulate the effect of reverberation in a large hall or cavern one or several delayed signals are added to the original signal To be perceived as echo the delay has to be of order 35 millis
13. AM Ple 512104 edd 11 2 21 Conversion and Modena icon 12 ZAS WO GU AON eau A as 12 2 Amplitude modulation AM EE 13 2 5 2 Fregueney modulation AFM herser Hew icesrasaen cutiadumt cle hsceneiesths ictal sa busca edad eae te 15 Ded SDC ia IOC UL AMOI ia 16 ZA Broadcast Ma ai 18 24 DEMO GUA CON reir li leeis 18 ZO MAPLE O A A sone een tne Stee an oe ere a een ee one 18 AN irre heed ences anna race ea wena easier E ee 19 2 6 Microwave and Satellite SyStemMs cccccccccccccccssssssccessssssseseesssescccccccccsesseeeeesssssssseeees 23 201 Satelite Based Fransiss ONS ars ii ege 23 2 6 2 Terrestrial Microwave Transmission sseoeeessssssssecerrsssssssscerrsssssssecereessssssseeeeessssss 23 2 6 3 Advantages of Microwave Transmsgeong 24 2 6 4 Satellite and Terrestrial Microwave Comparison cccccccsssessseeceeeeceeeeeeeeeeeeeeeeeaas 24 Za ENC OGING and DC COIN E 24 METHODOLOGY so ondo ea en ena ees 26 SEENEN 27 SEENEN 2J SS EE EE 2 ECON SUCIO Nico 28 E e EE 28 Si NUS ES APIO RAS od 29 LEC AMAIS E 29 IL T C ONN TOES dos 29 RE 30 3 2 1 Source coding and MPEG 2 multiplexing MI a 30 EE O 31 3 2 3 MUX adaptation and energy drsperaal 31 AL Etc mal encoder moricei a 31 iz Exe mal intercalan anny eee nT TT eve ern mer ney eine NE ee ee 31 32 0 Mle a encoder islas 31 SA A EE 31 ILSE M PPO eee nee nr rr Tien enn errr neN te pre NTT nT ey TOEetn yr ener See ey re Ia ne A 31 Da Pramo 210 A 521 6 18 WE 31 SE Le
14. DC and DAC are not necessary The DSP acts directly on the incoming signal eliminating irregularities caused by noise and thereby minimizing the number of errors per unit time 3 2 DVBT This is the transmission of digital signal multiplexed and using of the frequency spectrum much more efficiently Programme MUX Transport Video Encoder MUX Audio Encoder r lt 7 Splitter wm mm wm wm wm wm d Source coding and MPEG 2 multiplexing V MUX adaptation External External Internal Internal ii Geer here Gate energy encoder interleaver encoder Interleaver PP ee AA ech dispersal insertion frontend Mux gosto J External i External Internal energy A encoder m interleaver encoder TPS and pilot dispersal i signal mb O O A mmm mmm zl mmm mmm zl mmm zm zl Terrestrial channel adapter Figure 3 5 DVBT cycle 3 2 1 Source coding and MPEG 2 multiplexing MUX Compressed video compressed audio and data streams are multiplexed into MPEG program streams MPEG PSs One or more MPEG PSs are joined together into an MPEG transport stream MPEG TS this is the basic digital stream which is being transmitted and received by TV sets or home Set Top Boxes STB Allowed bitrates for the transported data depend on a number of coding and modulation parameters it can range from about 5 to about 32 Mbit s 30 3 2 2 Splitter Two different MPEG TS s can be t
15. Exciters Exciters are mostly found as plugins for sound editing software and in sound enhancement processors 3 7 2 Divider Afterwards the signal is advanced to the divider e 2 way or 5 way divider which fits into the respective route The RF output of the exciter is next led to the divider and phase shifter divided into five and corrected the phase 39 Figure 3 11 5 way divider block diagram 3 7 3 FET PA This is used to boost the output power of low power FM broadcast band exciters The following is the performance summary e 40W min output power e 88 to 108 MHz frequency range broadband e 20dB gain e 28V DC operation e High efficiency e Low component count e Integrated 7 pole Chebyshev low pass harmonic filter LPF O Single FET gain stage in class AB This design is based on the FET device with the attendant advantages of e High gain e High efficiency e Ease of tuning 40 Figure 3 12 Block diagram of FET PA 3 7 4 Filtering Signal is propagated for filtering to eliminate unwanted frequencies from the receiver signal While the correct filter settings can significantly improve the visibility of a defect signal incorrect settings can distort the signal presentation and even eliminate the defect signal completely Filtering is applied to the received signal and therefore is not directly related to the probe drive frequency as grasped in a time versus signal amplitude display With this display
16. FM Transmission 3 9 Analogue Transmission TV Due to the advent setbacks of analogue transmission in signal frequency constriction it has been scrubbed off air The High power capacity involved has also contributed to the same 46 Figure 3 18 A typical KBC Analogue transmitter The modulated signal is applied to a mixer also known as frequency converter Another input to the mixer which is usually produced in a crystal oven oscillator is known as subcarrier The two outputs of the mixer are the sum and difference of two signals Unwanted signal usually the sum is filtered out and the remaining signal is the RF signal Then the signal is applied to the amplifier stages The number of series amplifiers depends on the required output power The final stage is usually an amplifier consisting of many parallel power transistor systems In some of the model transmitters tetrodes or klystrons are also utilized The Analogue system put about 70 to 90 of the transmitters power into the sync pulses The remainder of the transmitter s power goes into transmitting the video s higher frequencies and the FM audio carrier The video signal modulates a carrier by a kind of amplitude modulation VSB modulation or C3F The modulation polarity is negative That means that the higher the level of the video signal the lower the power of the RF signal Channel 23 was in use with a frequency of 487 25 MHz and 10 kW power consumption 47 3 10 Dig
17. In the sampling controls the sampling rate was set to 44 1 kHz which is about 10 higher than the Nyquist Sampling Rate to allow cheaper reconstruction filters to be used 3 1 6 Anti Aliasing The sampling rate for an analog signal must be at least two times as high as the highest frequency in the analog signal in order to avoid aliasing Conversely for a fixed sampling rate the highest frequency in the analog signal can be no higher than one half of the sampling rate Any part of the signal or noise that is higher than one half of the sampling rate will cause aliasing In order to avoid this problem the analog signal gets to be filtered by a lowpass filter prior to being sampled anti aliasing filter Sometimes the reconstruction filter after a digital to analog converter is also called an anti aliasing filter 3 1 7 Converters On an incoming analog signal it is first converted to digital form by an analog to digital converter ADC The resulting digital signal has two or more levels Ideally these levels are always predictable exact voltages or currents However because the incoming signal contains noise the levels are not always at the standard values The DSP circuit adjusts the levels so they 29 are at the correct values This practically eliminates the noise The digital signal is then converted back to analog from via a digital to analog converter DAC If a received signal is digital for example computer data then the A
18. a in doing so The KBC Headquarters station contained the various production segments for signal production where processing was then undertaken in the respective control rooms Figure 3 1 KBC broadcasting production room 26 3 1 Signal processing 3 1 1 Sampling Values of the signal produced were recorded at given points in time For A D converters these points in time are equidistant The number of samples taken during one second is called the sample rate which are yet analogue values In the A D converters the sampling is carried out by a sample and hold buffer The sample andhold buffer splits the sample period in a sample time and a hold time In case of a voltage being sampled a capacitor is switched to the input line during the sample time During the hold time it is detached from the line and keeps its voltage 3 1 2 Quantization The analog voltage from the sample and hold circuit is represented by a fixed number of bits The input analog voltage is compared to a set of pre defined voltage levels represented by a unique binary number and the binary number that corresponds to the level that is closest to the analog voltage is chosen to represent that sample This process rounds the analog voltage to the nearest level which means that the digital representation is an approximation to the analog voltage for instance through dual slope or successive approximation Sampling Quantization Figure 3 2 Sampled and Quanti
19. ach sampler and we have the following rules for output If the input signal is higher than the current reference signal increase the reference by A and output a 1 If the input signal is lower than the current reference signal decrease the reference by A and output a 0 Some benefits of delta modulation are as follows 1 bit of resolution and therefore requires very little bandwidth and very little hardware No preset upper or lower bounds so Delta modulation can theoretically be used to modulate unbounded signals These benefits are countered by the problems of Slope Overload and Granular Noise which play an important role when designing a Delta Modulated system 16 Analog siznals Delta PWM sizal Figure 2 9 Delta Modulated System 2 3 3 1 Slope Overload If the input signal is rising or falling with a slope larger than A T where T is the sampling time we say that the sampler is suffering from Slope Overload In essence this means that in a Delta Modulation scheme we can never have slopes larger than a certain upper limit and functions that rise or fall at a faster rate are going to be severely distorted If the slope of m n Ts is greater than the slope of m n Ts Ts then Slope Overload distortion occurs 2 3 3 2 Granular Noise A problem with delta modulation is that the output signal must always either increase by a step or decrease by a step and cannot stay at a single value This means that if the inpu
20. adio telemetry radar seismic prospecting and monitoring newborns for seizures via EEG FM is widely used for broadcasting music and speech two way radio systems magnetic tape recording systems and some video transmission systems In radio systems frequency modulation with sufficient bandwidth provides an advantage in cancelling naturally occurring noise Frequency modulation is known as phase modulation when the carrier phase modulation is the time integral of the FM signal 15 2 3 3 Delta Modulation The sample values of analog waveforms of real world processes are very often predictable i e the average change from sample to sample is very small Hence we can make educated guess of what the next sample value depending on the current sample value Though there is error it is much less than peak to peak signal range This concept is used in Predictive coded modulation where instead of sending the signal it transmits just the prediction errors Delta Modulation employs Predictive coded modulation to simplify hardware MOOU LATOR CHANNEL DEM OCU LATOR Quartizer Integrator _ _ gt i gt Low pass 7 e fe Fiter Integrator d ll Figure 2 8 Delta Modulation Delta Modulation is strange in the fact that it attempts to represent an analog signal with a resolution of 1 bit This is accomplished by successive steps either up or down by a preset step size In delta modulation we have the stepsize A that is defined for e
21. alog signal processing This is for signals that have not been digitized as in legacy radio telephone radar and television systems This involves linear electronic circuits as well as non linear ones The former are for instance passive filters active filters additive mixers integrators and delay lines Nonlinear circuits include compandors multiplicators frequency mixers and voltage controlled amplifiers voltage controlled filters voltage controlled oscillators and phase locked loops Discrete time signal processing is for sampled signals defined only at discrete points in time and as such is quantized in time but not in magnitude Analog discrete time signal processing is a technology based on electronic devices such as sample and hold circuits analog time division multiplexers analog delay lines and analog This technology was a predecessor of digital signal processing and is still used in advanced processing of gigahertz signals The concept of discrete time signal processing also refers to a theoretical discipline that establishes a mathematical basis for digital signal processing without taking quantization error into consideration 2 1 4 Digital signal processing It is the processing of digitized discrete time sampled signals Processing is done by generalpurpose computers or by digital circuits such as ASICs field programmable gate arrays or specialized digital signal processors DSP chips Typical arithmetical opera
22. anges in light levels Bits per second for example a T 1 line carries 1 544Mbps and an E 1 line transports 2 048Mbps High bandwidth that can support high speed data and emerging applications that involve video and multimedia High multiplexers enable multiple conversations to share a communications channel and hence to achieve greater transmission efficiencies Good smart devices produce alerts alarms traffic statistics and performance measurements and technicians at a network control center NCC or network operations center NOC can remotely monitor and manage the various network elements Low because only two discrete signals the one and the zero need to be transmitted Good encryption can be used Low with twisted pair 10 7 that is 1 in 10 million bits per second will have an error with satellite 10 9 that is 1 in 1 billion per second will have an error and with fiber 10 11 that is only 1 in 10 trillion bits per second will have an error 9 Signal Analog signal is a continuous Digital signals are discrete time signal which represents physical signals generated by digital measurements modulation 11 Representation Uses continuous range of values Uses discrete or discontinuous to represent information values to represent information 12 Technology Analog technology records Samples analog waveforms into waveforms as they are a limited set of numbers and records them 13 Data
23. anslation of information is into binary format zero or one where each bit is representative of two distinct amplitudes Analogue transmission involves modulating a continuous beam of charged electromagnetic particles most commonly radio waves but also microwaves and visible light sent through Fibreoptic cables This project entails the analysis of the existing 100kw analogue transmitter paying attention to the respective parameters in modes of transmission that steer the principles of operation including the pros and cons in the transmission evolved The basic types of transmission based on how they modulate data to combine an input signal with a carrier signal are illustrated for instance AM and PM The implementation process is laid out including the process layout and power usage of the transmitter Relevant features are also laid in line such as bandwidth and noise involvement The mystery behind the involvement in a higher power capacity in analogue transmission was elaborated relative to digital transmission e the factor of wide ranges of frequencies and amplitudes explaining more consumption of power The digital transmitter is then set on design from the preceding transmitter to transmit binary data of less power capacity The setback of a narrow area of coverage is combated for instance using of boosters in between the stations was depicted The discrete messages are either represented by a sequence of pulses by means of a line
24. are fixed and can be directly calculated describing how the filter will react under different circumstances o a Impulse response H H H Amplitude 0 0 1 0 2 0 3 0 4 0 5 Frequency l 20 Log b Siep response Amplitude dB Figure 3 20 Digital Filter 50 The most straightforward way to implement a digital filter is by convolving the input signal with the digital filter s impulse response Recursion method could also be used The power is seen to drop to 4 207 kW from 10 kW in the system set up 3 10 3 Water cooling system The signal is then propagated to a pumping water cooling system to counter on the dissipated heat in the process The main utility of the cooling liquid is that the heat produced by the transmitter is transported outside the plant and is dissipated by the radiator on the external environment resulting in large savings in air conditioning The system uses two pumps one in reserve passive e in case the pump is working fails automatically activates the second The hydraulic system that allows this change is entirely mechanical in the outlet valves of the pump allowing liquid to flow only in one direction In this way simply turn on and off the pumps for the hydraulic circuit automatically adapts Figure 3 21 Technical data for respective parameters 51 NB For channel 26 the system yields 4 139 kW and a combiner is involved Figure 3 22 Block diagram for the dual driver
25. between every two existing samples In a linear system the value of the new sample a between existing samples n and m would be 2 2 19 Non Linear Interpolations Analog signals rarely have straight lines in them and therefore linear interpolation doesn t always produce a good approximation Nonlinear techniques can be used taking the surrounding points to produce a new point that isn t just an average value these methods are called non linear interpolation and there are too many of them for us to give a good example of each 2 2 20 Sampled Signals To process signals within a computer Digital Signal Processing requires that they be sampled periodically and then converted to a digital representation using an Analog to Digital Converter ADC To ensure accurate representation the signal must be sampled at a rate which is at least double the highest significant frequency component of the signal This is known as the Nyquist rate In addition the number of discrete levels to which the signal is quantized must also be sufficient to represent variations in the amplitude to the required accuracy Most ADCs quantize to 12 or 16 bits which represent 212 4096 or 216 65536 discrete levels After the signal has been processed it is often necessary to generate an analog output This function is performed by a Digital to Analog Converter DAC The reconstruction process generally involves holding the signal constant zero order hold during the pe
26. code baseband transmission or by a limited set of continuously varying wave forms passband transmission using a digital modulation method The passband modulation and corresponding demodulation also known as detection was carried out by modem equipment CODEC BCH IEEE ADC DL UL FDM GSM FEC MODEM DSP ABBREVIATIONS AND ACRONYMS Coder Decoder Broadcast Channel Institute of Electrical and Electronics Engineering Analogue to Digital Converter Downlink Uplink Frequency Division Multiplexing Global System for Mobile communications Forward correction error Modulator Demodulator Digital Signal Processing vi Figure 1 1 Figure 2 1 Figure 2 2 Figure 2 3 Figure 2 4 Figure 2 5 Figure 2 6 Figure 2 7 Figure 2 8 Figure 2 9 Figure 2 10 Figure 2 11 Figure 2 12 Figure 2 13 Figure 3 1 Figure 3 2 Figure 3 3 Figure 3 4 Figure 3 5 Figure 3 6 Figure 3 7 Figure 3 8 Figure 3 9 Figure 3 10 LIST OF FIGURES Analogue and Digital Signals Signal Processing Cycle Sampling a Signal Sampling Time Aliasing Modulation Amplitude Modulation Frequency Modulation Delta Modulation Delta Modulated System Multiplexing Frequency Division Multiplexing Time Division Multiplexing Encoding and Decoding KBC Broadcasting Production Room Sampled and Quantized Signal Quantization Aliasing DVBT Cycle Up Link of Signal Downlink of Signal Typical FM Transmi
27. different than the original data The primary benefit of digital signals is that they can be handled by simple standardized receivers and transmitters and the signal can be then dealt with in software which is comparatively cheap to change 2 1 Signal processing This is an enabling technology that encompasses the fundamental theory applications algorithms and implementations of processing or transferring information contained in many different physical symbolic or abstract formats broadly designated as signals It uses mathematical statistical computational heuristic and linguistic representations formalisms and techniques for representation modeling analysis synthesis discovery recovery sensing acquisition extraction learning security or forensics Electronic l Transducer Processors Transmitter D LV E Receiver Transducer Electromagnetic a wave DOO FE EX Figure 2 1 Signal processing cycle mi Electronic Cisna SIEMd 2 1 2 Typical devices involved Filters for example analog passive or active or digital FIR IIR frequency domain or stochastic filters etc Samplers and Analog to digital converters for Signal acquisition and reconstruction which involves measuring a physical signal storing or transferring it as digital signal and possibly later rebuilding the original signal or an approximation thereof Signal compressors Digital signal processors DSPs 2 1 3 An
28. e existing 100kw analogue transmitter to digital transmitter of less power capacity 1 2 1 Specific Objectives 1 To examine the analogue transmitter and its mode of operation based on the stages in which the signal passes through before transmission 2 The evolution and need of a Digital transmitter in providing a better platform in signal transmission and how power is attenuated in the mode appreciating the cons involved 3 Investigate how power is reduced in the latter mode and how this can be of benefit I imie Analog Signal ID ime Digital Signal Figure 1 1 Analogue and Digital signals 1 3 REPORT ORGANISATION This report is organized as follows the introduction is in chapter one In chapter two the literature review is presented followed by Methodology which is in chapter three Chapter four presents the Discussion of the project and finally conclusions and recommendations are discussed in chapter five CHAPTER 2 LITERATURE REVIEW Analog systems occur to be less tolerant to noise make good use of bandwidth and are easy to manipulate mathematically However analog signals require hardware receivers and transmitters that are designed to perfectly fit the particular transmission Digital signals are more tolerant to noise but digital signals can be completely corrupted in the presence of excess noise In digital signals noise could cause a 1 to be interpreted as a O and vice versa which makes the received data
29. e right channel and a multipair telephone cable Another example is a switched star network such as the analog telephone access network although inside the telephone exchange or between the exchanges other multiplexing techniques are typically employed or a switched Ethernet network A third example is a mesh network Wired space division multiplexing is typically not considered as multiplexing In wireless communication space division multiplexing is achieved by multiple antenna elements forming a phased array antenna Examples are multiple input and multiple output MIMO single input and multiple output SIMO and multiple input and single output MISO multiplexing For example an IEEE 802 11n wireless router with k number of antennas makes it in principle possible to communicate with k multiplexed channels each with a peak bit rate of 54 Mbit s thus increasing the total peak bit rate with a factor k Different antennas would give different multi path propagation echo signatures making it possible for digital signal processing techniques to separate different signals from each other These techniques may also be utilized for space diversity improved robustness to fading or beamforming improved selectivity rather than multiplexing 2 5 1 2 Frequency division multiplexing Frequency division multiplexing FDM The spectrum of each input signal is shifted to a distinct frequency range Frequency division multiplexing FDM is inherentl
30. e with the un delayed signal and create a flanging effect Equalization different frequency bands are attenuated or boosted to produce desired spectral characteristics Moderate use of equalization often abbreviated as EQ can be used to fine tune the tone quality of a recording extreme use of equalization such as heavily cutting a certain frequency can create more unusual effects Filtering Equalization is a form of filtering In the general sense frequency ranges can be emphasized or attenuated using low pass high pass band pass or band stop filters Pitch shift this effect shifts a signal up or down in pitch For example a signal may be shifted an octave up or down This is usually applied to the entire signal and not to each note separately Blending the original signal with shifted duplicate s can create harmonies from one voice Another application of pitch shifting is pitch correction Here a musical signal is tuned to the correct pitch using digital signal processing techniques Time stretching the complement of pitch shift that is the process of changing the speed of an audio signal without affecting its pitch Resonators emphasize harmonic frequency content on specified frequencies These may be created from parametric EQs or from delay based comb filters Robotic voice effects are used to make an actor s voice sound like a synthesized human voice Synthesizer generate artificially almost any sound by eithe
31. econds or above Short of actually playing a sound in the desired environment the effect of echo can be implemented using either digital or analog methods Analog echo effects are implemented using tape delays and or spring reverbs When large numbers of delayed signals are mixed over several seconds the resulting 32 sound has the effect of being presented in a large room and it is more commonly called reverberation or reverb for short Flanger to create an unusual sound a delayed signal is added to the original signal with a continuously variable delay usually smaller than 10 ms This effect is now done electronically using DSP but originally the effect was created by playing the same recording on two synchronized tape players and then mixing the signals together Phaser another way of creating an unusual sound the signal is split a portion is filtered with an all pass filter to produce a phase shift and then the unfiltered and filtered signals are mixed The phaser effect was originally a simpler implementation of the flanger effect since delays were difficult to implement with analog equipment Phasers are often used to give a synthesized or electronic effect to natural sounds such as human speech Chorus a delayed signal is added to the original signal with a constant delay The delay has to be short in order not to be perceived as echo but above 5 ms to be audible If the delay is too short it will destructively interfer
32. gnal of carrier frequency up to 10mW The HPB 1211 FM TR PA amplifies the RF signal from 2W to 20W when it is forced air cooling or 15W when it is convection cooling as output of the FM exciter The synthesized PLL Phase locked loop circuit for carrier frequency regulation which is located on the mother board divides the RF sample from the FM modulator into I N compares with the high stable crystal oscillator and feeds back the difference between them into the FM modulator A value of N can be preset with the switches and it can be preset for a maximum 8channel with the HPB 1215 channel selector board option to make n 1 standby configuration 3 10 2 Filter Digital filters are used for two general purposes 1 Separation of signals that have been combined needed when a signal has been contaminated with interference noise or other signals 2 Restoration of signals that have been distorted in some way Analog filters can be used for these same tasks however digital filters are seen to achieve far superior results 49 Note Analog filters are cheap fast and have a large dynamic range in both amplitude and frequency Digital filters in comparison are vastly superior in the level of performance that can be achieved The digital filter has an impulse response a step response and a frequency response containing complete information about the filter but in a different form If one of the three is specified the other two
33. he HPF only allow those frequencies in the blue area to pass Therefore it can be seen that with these settings there are no frequencies that pass i e the frequencies Passed by the LPF are filtered out by the HPF and vice versa Signal Attenuation dB O 10 20 30 40 50 60 70 80 90 100 Frequency Hz O Low Pass Filter MA High Pass Filter Figure 3 13 Filter effects To create a window of acceptance for the signals the filters need to overlap The area shown in gray is where the two frequencies overlap and the signal is passed A signal of 30Hz will get through at full amplitude while a signal of 15Hz will be attenuated by approximately 50 All frequencies above or below the gray area the pass band will be rejected by one of the two filters 42 Signal Attenuation dB O 10 20 30 40 50 60 70 80 Dm 100 Frequency HZ CO Low Pass Filter MA High Pass Filter Figure 3 14 Filter effects 3 7 4 3 Use of Filters The main function of the LPF is to remove high frequency interference noise This noise can come from a variety of sources including the instrumentation and or the probe itself The noise appears as an unstable dot that produces jagged lines on the display as seen in the signal from a surface notch shown in the left image below Lowering the LPF frequency will remove more of the higher frequencies from the signal and produce a cleaner signal as shown in the center image below When using a LPF it should be
34. he audio picture intensity and picture chrominance This process makes use of two subcarriers Other transmissions such as satellite TV and long distance telephone transmission make use of multiple subcarriers for the broadcast of multiple signals simultaneously 2 4 Demodulation This is the act of extracting the original information bearing signal from a modulated carrier wave A demodulator is an electronic circuit or computer program in a software that is used to recover the information content from the modulated carrier wave There are many types of modulation so there are many types of demodulators The signal output from a demodulator may represent sound an analog audio signal images an analog video signal or binary data a digital signal 2 5 Multiplexing This is a method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium The aim is to share an expensive resource For instance several signals from different media may be carried using one stream channel The multiplexed 18 signal is transmitted over a communication channel which may be a physical transmission medium The multiplexing divides the capacity of the low level communication channel into several high level logical channels one for each message signal or data stream to be transferred A reverse process known as demultiplexing can extract the original channels on the receiver side Figure 2 1
35. ider an application requiring four terminals at an airport to reach a central computer Each terminal communicated at 2400 baud so rather than acquire four individual circuits to carry such a low speed transmission the airline has installed a pair of multiplexers A pair of 9600 baud modems and one dedicated analog communications circuit from the airport ticket desk back to the airline data center are also installed Mux Demux Conversation A Conversation A nvesaton E y gn Conversation C gt e OO Sonversation D 3 p Figure 2 12 Time Division Multiplexing Some modern web proxy servers e g polipo use TDM in HTTP pipelining of multiple HTTP transactions onto the same TCP IP connection 2 21 Carrier sense multiple access and multidrop communication methods are similar to timedivision multiplexing in that multiple data streams are separated by time on the same medium but because the signals have separate origins instead of being combined into a single signal are best viewed as channel access methods rather than a form of multiplexing 2 5 1 4 Polarization division multiplexing Polarization division multiplexing uses the polarization of electromagnetic radiation to separate orthogonal channels It is in practical use in both radio and optical communications particularly in 100 Gbit s per channel fiber optic transmission systems 2 5 1 5 Orbital angular momentum multiplexing Orbital angular momentum multiplexing is a relati
36. in proportion to that of a variable It could be the transfer of an analog source signal using an analog modulation method such as frequency modulation FM or amplitude modulation AM or no modulation at all Analog transmission can be conveyed in many different fashions e g Twisted pair or coax cable fiber optic cable via air water etc There are two basic kinds of analog transmission both based on how they modulate data to combine an input signal with a carrier signal Usually this carrier signal is a specific frequency and data is transmitted through its variations The two techniques are amplitude modulation AM which varies the amplitude of the carrier signal and frequency modulation FM which modulates the frequency of the carrier Digital signals are discrete in time and value Digital signals are signals that are represented by binary numbers 1 or 0 The 1 and O values can correspond to different discrete voltage values and any signal that doesn t quite fit into the scheme just gets rounded off Digital signals are sampled quantized amp encoded version of continuous time signals which they represent In addition some techniques also make the signal undergo encryption to make the system more tolerant to the channel The process of converting from analog data to digital data is called sampling The process of recreating an analog signal from a digital one is called reconstruction 1 2 Objectives To analyze th
37. ital TV Transmission This is the transmission of audio and video by digitally processed and multiplexed signal in contrast to the totally analog and channel separated signals used by analog television Digital TV can support more than one program in the same channel bandwidth Digital Video Broadcasting DVB used coded orthogonal frequency division multiplexing OFDM modulation and supports hierarchical transmission Figure 3 19 KBC Digital TV Transmitter 48 3 10 1 Exciter Channel 37 An exciter is basically is a low powered transmitter up to a couple hundred watts which drives a power amplifier system which would output several thousand watts or more The exciter generates the carried frequency digitally generated on modern transmitters crystal generated on old ones and modulate it with the incoming audio usually composite sometimes discrete left right or even digital on modern transmitters and output an RF carrier which can directly drive an antenna to the output power of the exciter The audio signal fed to the exciter is led to the HPB 1212 Stereo Modulator card or HPB 1213 mono operation for conversion into a stereo composite signal or monaural signal The signal is fed through U link located on the front panel and it is combined with the auxiliary signal through the HPB 1210 mother board and fed to the FM modulator This FM modulator uses the DCFM Direct carrier frequency modulation system to emit an RF si
38. ivated right image With the HPF looping signals with a positive and similar negative deflection are produced on the impedance plane 3 7 5 Combiner The signal combiner receives signals from all receiving antennas and provides a combination technique with performance close to optimal maximal ratio combiners but without the complexity The invention provides a base station arrangement which only processes the outputs from antennas which contribute positively to the overall system carrier to noise ratio Figure 3 15 A typical transmission combiner 44 3 8 Graceful Degradation This is the property that enables a system to continue operating properly in the event of the failure of some of its components The choice of the RF composition and its bias is fundamental in order to guarantee the ON AIR service also during some subsystem fault The output power is always present even if there are 3 broken pallets Obviously the output power will be reduced a percentage obtainable by the formula co 122 Where M Total number of amplifiers in parallel N Failures amplifiers M N G Duib 20 Log Incoming radio ENS Radio H SG e Se e 9 ee OSS SOS SOS SOTTO SSS SSCS SASS S ESOS eee e a e e e e Figure 3 16 A typical FM transmission block diagram 45 Studio Signal Receiver Processing Combiner Filter Divider Amplification Exciter Demodulation Transmission Decoding Figure 3 17 The block diagram for
39. iver 2 7 Encoding and Decoding The process of encoding converts information from a source into symbols for communication or storage Encoding converts data in one format to another format Encoding is typically done to utilise one or more of the following advantages e Compression of data for more efficient data transfers or storage e Improve the quality of a transmission signal digital encoding is often used to recude the effect of noise and signal attenuation e Remove unneeded information relative to the application digital TV signals consider the quality of human vision and encode the signal accordingly animals who can see at higher rates than us such as birds would be very unimpressed with what they see on the TV e Convert data into a format to communicate with attached peripherals O Encrypt data for security reasons Decoding is the reverse process converting code symbols back into a form that the recipient understands 24 EA MODO EA Compensation Mar Inter inverse Select Ee VQuantizathon Pre Ee tion Hoi Ez Ez J Motion intra Compensation iransiorny Inter Select inverse Ouantizatbon int Fal Prediction Entrop Spy De Blocung Coding y Filter Figure 2 13 Encoding and Decoding 25 CHAPTER 3 METHODOLOGY This chapter seeks to illustrate the processes involved in the transmission of a signal from a broadcasting channel Kenya Broadcasting Channel provided the criteri
40. lid coding rates 1 2 2 3 3 4 5 6 and 7 8 3 2 7 Internal interleaver Data sequence is rearranged again aiming to reduce the influence of burst errors This time a block interleaving technique is adopted with a pseudo random assignment scheme this is really done by two separate interleaving processes one operating on bits and another one operating on groups of bits 3 2 8 Mapper The digital bit sequence is mapped into a base band modulated sequence of complex symbols There are three valid modulation schemes QPSK 16 QAM 64 QAM 3 2 9 Frame adaptation The complex symbols are grouped in blocks of constant length 1512 3024 or 6048 symbols per block A frame is generated 68 blocks long and a superframe is built by 4 frames 31 3 2 10 Pilot and TPS signals In order to simplify the reception of the signal being transmitted on the terrestrial radio channel additional signals are inserted in each block Pilot signals are used during the synchronization and equalization phase while TPS signals Transmission Parameters Signaling send the parameters of the transmitted signal and to unequivocally identify the transmission cell The receiver must be able to synchronize equalize and decode the signal to gain access to the information held by the TPS pilots Thus the receiver must know this information beforehand and the TPS data is only used in special cases such as changes in the parameters resynchronizations etc 3 2 1
41. n audio signal or TV signal over an analog bandpass channel at a different frequency for example over a limited radio frequency band or a cable TV network channel Analog and digital modulation facilitate frequency division multiplexing FDM where several low pass information signals are transferred simultaneously over the same shared physical medium using separate passband channels several different carrier frequencies The aim of digital baseband modulation methods also known as line coding is to transfer a digital bit stream over a baseband channel typically a non filtered copper wire such as a serial bus or a wired local area network The aim of pulse modulation methods is to transfer a narrowband analog signal for example a phone call over a wideband baseband channel or in some of the schemes as a bit stream over another digital transmission system In music synthesizers modulation may be used to synthesize waveforms with an extensive overtone spectrum using a small number of oscillators In this case the carrier frequency is typically in the same order or much lower than the modulating waveform See for example frequency modulation synthesis or ring modulation synthesis 2 3 1 Amplitude modulation AM It is a modulation technique used in electronic communication most commonly for transmitting information via a radio carrier wave In amplitude modulation the amplitude signal strength of the carrier wave is varied in propo
42. n towers are speckled with antennas pointing in many directions they actually point at different microwave transmission towers The absorption of microwaves in the atmosphere also means that there is very little interference between different microwave towers Example is the airing of live broadcast from Kenyan parliament 23 2 6 3 Advantages of Microwave Transmissions Radio including microwaves is a form of energy transmission Energy transmission at frequencies and wavelengths that are defined as microwaves tend to be absorbed by water molecules This is why a microwave oven works For microwave transmission the water molecules in the atmosphere absorb the transmitted energy The effect required for transmission is comparatively low for the amount of data transmitted because of the short distances afforded by the line of sight requirement This is also true for satellites A satellite can transmit at a relatively low effect since there is nothing between it and the antenna 2 6 4 Satellite and Terrestrial Microwave Comparison Satellite communications only work when there is a line of sight from the communications satellite So does terrestrial microwave communications Both require parabolic antennas This is because apart from the limited frequency bands used by satellite communications terrestrial and satellite microwave communications are actually using the same technology and the only difference is the distance between sender and rece
43. ng to ShannonHartley theorem and that multi path propagation in wireless communication can be combated by rake receivers 2 5 1 7 Forward error correction FEC This is a technique used for controlling errors in data transmission over unreliable or noisy communication channels The central idea is the sender encodes his message in a redundant way by using an error correcting code ECC 2 6 Microwave and Satellite Systems Both satellite and ground based transmissions can use microwaves which formally are defined as electromagnetic radiation in the wavelength range 0 3 to 0 001 meters with a frequency between 100 megahertz and 30 gigahertz This means the waves fall in the spectrum normally used for radar But both terrestrial and satellite based microwave transmissions conform to the same physical conditions 2 6 1 Satellite Based Transmissions The C band uses frequencies between 3 7 and 4 2 GHz and from 5 9 to 6 4 GHz The Ku band satellites use frequencies between 11 and 12 GHz Both types of communications require ground based receivers to have a parabolic antenna to receive the signal The antenna also has to be directed toward the satellite so that it focuses the parabola on the satellite transmission 2 6 2 Terrestrial Microwave Transmission Microwave transmission in the atmosphere can only take place when there is a direct line of sight between the sender s and receiver s antenna point to point This is why microwave transmissio
44. on can be transported through a noisy channel without degradation e Integrated networks Disadvantages of Digital Transmission e Sampling Error e Digital communications require greater bandwidth than analogue to transmit the same information e The detection of digital signals requires the communications system to be synchronized whereas generally speaking this is not the case with analogue systems 57 Feature 1 Signal 2 Traffic measurement 3 Bandwidth 4 Network capacity 5 Network manageability 6 Power requirement 7 Security 8 Error rates Continuously variable in both amplitude and frequency Hz for example a telephone channel is 4KHz Low bandwidth 4KHz which means low data transmission rates up to 33 6Kbps because of limited channel bandwidth Low one conversation per telephone channel Poor a lot of labor is needed for network maintenance and control because dumb analog devices do not provide management information streams that allow the device to be remotely managed High because the signal contains a wide range of frequencies and amplitudes Poor when you tap into an analog circuit you hear the voice stream in its native form and it is difficult to detect an intrusion High 10 5 bits that is 1 in 100 000 bits is guaranteed to have an error 58 Analog Characteristics Digital Characteristics Discrete signal represented as either changes in voltage or ch
45. ors including the signed unsigned number scheme in use by the converter the resolution and the step size 2 2 10 Step Size The step size of a sampler is the range of analog values that can be input before a bit is changed in the sampler Note however that bipolar converters are generally symmetric That is they have the same amount of range below zero as they do above zero If we want a converter that goes from 5V to 25V we are going to need to get a converter that can handle from 25V to 25V which mean we are wasting at least 2 5ths of the possible range of the device 2 2 11 Bitrate The number of bits created per sample times the sampling frequency gives us the rate at which we are producing data bits This rate is called the bitrate and is frequently denoted as rp or simply r If we have a sampling time of T seconds then the bitrate and the resolution are related as such Where r is measured in units of bits second T is measured in seconds and n is measured in bits 2 2 12 Bandwidth Bandwidth denoted with a W is the frequency range needed to transmit an analog or digital signal Bandwidth is related to the bitrate as follows W 2 Pb This is for a bare unmodulated bit stream This value can change depending on what modulation scheme is used if any 2 2 13 Down Sampling There are occasions when the sampler is producing samples too fast or too slow for the rest of your circuit When the sampler is producing too
46. r imitating natural sounds or creating completely new sounds Modulation To change the frequency or amplitude of a carrier signal in relation to a predefined signal 33 e Compression the reduction of the dynamic range of a sound to avoid unintentional fluctuation in the dynamics Level compression is not to be confused with audio data compression where the amount of data is reduced without affecting the amplitude of the sound it represents e 3D audio effects place sounds outside the stereo basis e Active noise control a method for reducing unwanted sound e Wave field synthesis a spatial audio rendering technique for the creation of virtual acoustic environments 3 4 Encryption This includes two components a digitizer to convert between speech and digital signals and an encryption system to provide confidentiality through the use of Voice Coders vocoders to achieve tight bandwidth compression of the signals Ensures that the sent signal is ready only for transmission avoiding any content alterations 3 5 Up link The signal is then send to the transmission sites via uplink or satellite depending on the signal content distance and its mode of airing 34 Figure 3 6 Uplink of Signal 3 6 Downlink The signal is received at the transmission site ready for transmission through the downlink equipment 35 Figure 3 7 Downlink from the production site 3 7 Analogue FM Transmission Radio The receiver picks
47. ransmitted at the same time using a technique called Hierarchical Transmission It may be used to transmit for example a standard definition SDTV signal and a high definition HDTV signal on the same carrier Generally the SDTV signal is more robust than the HDTV one At the receiver depending on the quality of the received signal the STB may be able to decode the HDTV stream or if signal strength lacks it can switch to the SDTV one in this way all receivers that are in proximity of the transmission site can lock the HDTV signal whereas all the other ones even the farthest may still be able to receive and decode an SDTV signal 3 2 3 MUX adaptation and energy dispersal The MPEG TS is identified as a sequence of data packets of fixed length 188 bytes With a technique called energy dispersal the byte sequence is decorrelated 3 2 4 External encoder A first level of error correction is applied to the transmitted data using a non binary block code a Reed Solomon RS 204 188 code allowing the correction of up to a maximum of 8 wrong bytes for each 188 byte packet 3 2 5 External interleaver Convolutional interleaving is used to rearrange the transmitted data sequence in such a way that it becomes more rugged to long sequences of errors 3 2 6 Internal encoder A second level of error correction is given by a punctured convolutional code which is often denoted in STBs menus as FEC Forward error correction There are five va
48. riod between samples as shown in the following figure This signal is then cleaned up by passing it through low pass filter to remove high frequency components generated by the sampling process 11 2 2 21 Conversion Codecs and Modems e Acodec which is a contraction of coder decoder converts analog signals into digital signals There are different codecs for different purposes For the PSTN for example there are codecs that minimize the number of bits per second required to carry voice digitally through the PSTN In cellular networks because of the constraints and available spectrum a codec needs to compress the voice further to get the most efficient use of the spectrum Codecs applied to video communication also require very specific compression techniques to be able to move those high bandwidth signals over what may be somewhat limited channels today e Amodem which is a contraction of modulator demodulator is used to infuse digital data onto transmission facilities Some modems are designed specifically to work with analog voice grade lines There are also modems that are designed to work specifically with digital facilities for example ISDN modems and ADSL modems A modem manipulates the variables of the electromagnetic wave to differentiate between the ones and zeros 2 3 Modulation Modulation is the process of conveying a message signal for example a digital bit stream or an analog audio signal inside another signal that
49. rough Microwave and long distance transmission is aired via satellite 54 Figure 3 25 A typical transmitter 3 10 7 Decoding On the receivers end the consumer gets to decode the obtained signal e undoing the encoding so that the original information can be retrieved through a decoder to view the respective frequencies separately from the single stream 55 CHAPTER 4 DISCUSSION 4 1 Analogue transmission Analog signals were seen to be continuous signal which represents physical measurements denoted by sine waves whereas Digital signals are discrete time signals generated by digital modulation denoted by square waves The analog transmission lacked complex multiplexing procedures and timing equipment operating at high power capacities due to the continuity nature involved It formed a wider broadcast area i e Could travel over long distances due to the continuous trait However in situations where a signal often has high signal to noise ratio and cannot achieve source linearity or in long distance high output systems analog is unattractive due to attenuation problems The main advantage is the fine definition of the analog signal which has the potential for an infinite amount of signal resolution Compared to digital signals analog signals are of higher density Another advantage with analog signals is that their processing may be achieved more simply than with the digital equivalent An analog signal may be processed
50. rtion to the waveform being transmitted That waveform may for instance correspond to the sounds to be reproduced by a loudspeaker or the light intensity of television pixels This technique contrasts with frequency modulation in which the frequency of the carrier signal is varied and phase modulation in which its phase is varied 13 2 3 1 2 Amplitude modulation methods A low frequency message signal top may be carried by an AM or FM radio wave In analog modulation the modulation is applied continuously in response to the analog information signal Common analog modulation techniques are Y Amplitude modulation AM here the amplitude of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal Double sideband modulation DSB Double sideband modulation with carrier DSB WC used on the AM radio broadcasting band Double sideband suppressed carrier transmission DSB SC S Double sideband reduced carrier transmission DSB RC Single sideband modulation SSB or SSB AM SSB with carrier SSB WC SSB suppressed carrier modulation SSB SC Vestigial sideband modulation VSB or VSB AM Quadrature amplitude modulation QAM Angle modulation which is approximately constant envelope LN NNN NNN S Frequency modulation FM here the frequency of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal Phase modulation PM
51. set to the highest frequency that produces a usable signal To reduce noise in large surface or ring probes it may be necessary to use a very low LPF setting down to 10Hz The lower the LPF setting the slower the scanning speed must be and the more closely it must be controlled The image on the right below shows a signal that has been clipped due to using a scan speed too fast for the selected HPF setting The HPF is used to eliminate low frequencies which are produced by slow changes such as conductivity shift within a material varying distance to an edge while scanning parallel to it or out of round holes in fastener hole inspection The HPF is useful when performing automated or semiautomatic scans to keep the signal from wandering too far from the null balance point The most common application for the HPF is the inspection of fastener holes using a rotating scanner As the scanner rotates at a constant RPM the HPF can be adjusted to achieve the desired effect Use of the HPF when scanning manually is not recommended as keeping a constant scanning speed is difficult and the signal deforms and amplitude decreases 43 The size of a signal decreases as the scan speed decreases and a flaw indication can be eliminated completely if the scan is not done with sufficient speed In the images below it can be seen that a typical response from a surface notch in aluminum without HPF left image looks considerably different when the HPF is act
52. st 10 times faster than your input signal When designing a system there are 2 ways to prevent ultrasonic sounds or other unwanted high frequency noise from aliasing to a lower frequency becoming audible noise e Adjust the capacitors or other components of the anti aliasing filter so it blocks all frequencies more than half the sampling rate e Adjust the sampling rate to more than twice the frequency of the highest frequency passed by the anti aliasing filter 2 2 7 Resolution The resolution of a sampler is the number of bits that are used to represent each signal For instance a 12 bit sampler will output 12 bits of data for every sample This means that there are 2 possible digital values that each sample can be converted to In general the more bits of resolution the better more faithful the digital signal will be to the original The resolution n is related to the number of steps m by the following formula 2 2 8 Unipolar and Bipolar Samplers come in two basic varieties unipolar and bipolar Basically unipolar samplers only take positive values and only output unsigned digital values Bipolar converters can take positive and negative values and output signed digital values It is important to note that bipolar converters are generally symmetrical that is that they have the same number of bits for expressing negative and positive numbers 2 2 9 Sample Range The range of possible samples is dependant on a number of fact
53. t signal is level the output signal could potentially be oscillatory That is the output signal would appear to be a wave because it would go up and down regularly This phenomena is called Granular Noise When used in ADCs Analog to Digital Converters this problem can be solved by internally adding additional bit s of resolution that correspond to the value of A This way the LSBs Least significant bits that were added can be ignored in the final conversion result 17 2 3 3 3 Delta Sigma Modulation A delta sigma ADC also called a sigma delta ADC use the delta modulation technique internally 2 3 4 Broadcast Signals Radio communication is typically in the form of AM radio or FM Radio transmissions The broadcast of a single signal such as a monophonic audio signal can be done by straightforward amplitude modulation or frequency modulation More complex transmissions utilize sidebands arising from the sum and difference frequencies which are produced by superposition of some signal upon the carrier wave For example in FM stereo transmission the sum of left and right channels L R is used to frequency modulate the carrier and a separate subcarrier at 38 kHz is also superimposed on the carrier That subcarrier is then modulated with a L R or difference signal so that the transmitted signal can be separated into left and right channels for stereo playback In television transmission three signals must be sent on the carrier t
54. tention of passing it off as his her own work 5 understand that any false claim in respect of this work shall result in disciplinary action in accordance with University anti plagiarism policy This project report has been submitted for examination to the Department of Electrical and Information Engineering University Of Nairobi with my approval as the supervisor PROF MAURICE MANGOLI Date nasas DEDICATION I would like to dedicate this Project to my family for their moral and financial support during the period of my studies ACKNOWLEDGEMENT would like to take this opportunity and deeply thank Prof Maurice Mangoli for his supervision and constant guidance in the accomplishment of the project and providing the means to obtain the respective resources and access relevant in the implementation of this project lam also thankful to Mr Imbira Ayub ICT and Technical Services Manager and this Technical team at Kenya Broadcasting Channel KBC for the assistance and arranging the means through which this project was applied want to express my appreciation and gratitude to my Parents and Uncles Mr Omar Khamis Mr Ali Mandhry and Mr Soud Mandhry deceased for their financial support backing and continuous encouragement throughout during my whole study term Thank you all and God bless ABSTRACT In the analog technology information is translated into electric pulses of varying amplitude while in digital technology tr
55. the input function with an impulse centered at the sampling time T the output will be the value of the input function at time T More specifically our output will be the sample at time T Here is the definition f T f t t T Where f T is the samples value at time T 2 2 5 Aliasing If a sampler is only reading in values at particular times it can become confused if the input frequency is too fast The resulting problem is called Aliasing and is a major factor in Sampler design When the input signal frequency was faster than half the sampling frequency the sampled result appears to be a low frequency wave mn e Es la ra IV d i I i ri l A dl ii i i j L AN j i Ki pol d T i Jil H KA i FAA PEN EA ee A aT d I J E 1 L d II O 1 Wt i l j i i ga ili Fo lj l T d d i i y j T w 4 j ech o 12 3 4 5 6 7 1 Figure 2 4 Aliasing 2 2 6 Nyquist Sampling Rate To avoid the problem of aliasing the Nyquist Sampling Rate should be considered the slowest possible sampling rate Any slower than the Nyquist sampling rate and the sampler is in danger of producing an aliased signal The Nyquist sampling rate is two times the highest frequency of the input signal The Nyquist sampling rate is a bare minimum and it is recommended that samplers sample much faster than the minimum For instance one common guideline says that it should sample at lea
56. tions include fixedpoint and floating point real valued and complex valued multiplication and addition Other typical operations supported by the hardware are circular buffers and look up tables Examples of algorithms are the Fast Fourier transform FFT finite impulse response FIR filter Infinite impulse response IIR filter and adaptive filters such as the Wiener and Kalman filters 2 1 5 Nonlinear signal processing Involves the analysis and processing of signals produced from nonlinear systems and can be in the time frequency or spatio temporal domains Nonlinear systems can produce highly complex behaviors including bifurcations chaos harmonics and subharmonics which cannot be produced or analyzed using linear methods 2 2 Sampling Sampling is the reduction of a continuous signal to a discrete signal For every T seconds the sampler reads the current value of the input signal at that exact moment The sampler then holds that value on the output for T seconds before taking the next sample We have a generic input to this system f t and our sampled output will be denoted f t We can then show the following relationship between the two signals f t f 0 u O u T f T u T u 2T Note that the value of f at time t 1 5T T This relationship works for any fractional value D _ Ae e Bn Las Hi Analog Signa Sampled Points Voltage 4 4 4 i 4 lime combit x m xi mtd UH st
57. transmissions Subjected to deterioration by Can be noise immune without noise during transmission and deterioration during transmission write read cycle and write read cycle 14 Response to Noise More likely to get affected Less affected since noise reducing accuracy response are analog in nature 59 CHAPTER 5 CONCLUSION AND RECOMMENDATIONS 5 1 Conclusion In conclusion an analysis was undertaken to an analogue transmitter of 100 kW laying in points the modes of operations and its pros and cons involved A digital transmitter was then set on design from the preceding analysis and the distinctive features it contained to transmit frequencies in a more compact stream through multiplexing 5 2 Recommendations e Linearity improvement in analog transmission A method and system for improving the linearity of an analog transmission in a multichannel fiber optic transmission system uses a power series correction derived from a non information bearing portion of a received transmission A notch filter reduces the energy in a portion of a guard band between channels before transmission so that the energy in the notch filtered portion of the received transmission is indicative of the non linarites introduced by the analog transmission system This could in turn minimize noise intrusion upon transmission and yield a more reliable signal by decreasing the error rate e Boosting up security personnel at the transmission sites The sec
58. tter FM Modulation Exciter Stages vil Figure 3 11 Figure 3 12 Figure 3 13 Figure 3 14 Figure 3 15 Figure 3 16 Figure 3 17 Figure 3 18 Figure 3 19 Figure 3 20 Figure 3 21 Figure 3 22 Figure 3 23 Figure 3 24 5 way Divider Block Diagram FET PA Block Diagram Filter Effects A Filter Effects B Transmission Combiner FM transmission Block Diagram A FM transmission Block Diagram B Typical KBC Analogue Transmitter KBC Digital TV Transmitter Digital Filter Technical Data for Respective Parameters Dual Driver Block Diagram Dummy Load Model Pie chart display of Signal content Figure 3 25 Transmitter viii TABLE OF CONTENTS Contents LI ACK around OSEA Veneto der iria dotar Eonia dlrs 1 A ee 2 UN Specie OD EK 2 L REPORFORGANDGATION D 3 LITERATURE REVIEW E 4 EE 4 212 IN Pica GEVICES ANY E 5 2 1 3 Analog signal E 5 GE OAS AL signal PROCES S11 EE 5 Zila Nonlinear SIS MAL NOC S SIO genes acter O o o O T 6 Ne aaa 6 AE Kee ME 7 AS A e ER o UU E E 7 DS AUDIO WEAS rr naaa 7 Zi eer ITN un POR E EE E E E 7 A A o N 8 LAN QUISE apo TR AUC co 8 AN E 9 22 AAA O IN A 9 E o A EA 9 Dis DAN SUC EE 9 GR E 9 DIA A LING e A OO O E AE EE E E 10 ASA DOW P A e Po E eects te ose eaten 10 IEA ER OO ALM IN aera hop ce rn A PI UE OC E E ET 10 ULA AA o eenie tales euaii eden See E E metvones 10 A e o sence 10 2 219 Lincar Interpola ON AAA 11 22 49 Non linear Interpolation Sasa ii 1 D2 DW S
59. urity levels at the transmission sites were compromised as access within was quite easy and this provided a vulnerable area for alterations and signal manipulation 60 REFERENCES User manual AO8DT 5 2 1 3 2 3 Series Liquid Cooled Multistandard ITU DVB T DVB T2 ISDBT ATSC DAB Liquid Cooled FM and TV Transmitters http www antenaslatinas com en news liquid cooled fm and tv transmitters Online Data transmission Analogue transmission http en kioskea net contents 697 data transmission analogue transmission Online DVB T http en wikipedia org wiki DVB T Online TV Broadcast http igorfuna com dvb t Online Digital Filters The Scientist and Engineer s Guide to Digital Signal Processing By Steven W Smith Ph D Google Book Digital Signal Processing htto en wikibooks org wiki Digital Signal Processing Digital Filters Wikibook 61
60. ve generated at transmitter Frequency Modulated SA a carrier wave the ijl J Electrical image FM Radio signal that FUN of sound formed is transmitted Fd e by microphone Sound signal to microphone Figure 3 9 FM Modulation The stages involved in the transmission are as stated 3 7 1 Exciter The signal is passed through the exciter where amplification is undertaken and the phase is synchronized with the carrier wave The power capacity of this by then is amounted to be 10mw 38 Figure 3 10 Exciter stages An exciter is used to enhance a signal by dynamic equalization phase manipulation harmonic synthesis of usually high frequency signals and through the addition of subtle harmonic distortion Dynamic equalization involves variation of the equalizer characteristics in the time domain as a function of the input Due to the varying nature noise is reduced compared to static equalizers Harmonic synthesis involves the creation of higher order harmonics from the fundamental frequency signals present in the recording As noise is usually more prevalent at higher frequencies the harmonics are derived from a purer frequency band resulting in clearer highs Exciters are also used to synthesize harmonics of low frequency signals to simulate deep bass in smaller speakers Originally made in valve tube based equipment they are now implemented as part of a digital signal processor often trying to emulate analogue
61. vely new and experimental technique for multiplexing multiple channels of signals carried using electromagnetic radiation over a single path 3 It can potentially be used in addition to other physical multiplexing methods to greatly expand the transmission capacity of such systems As of 2012 it is still in its early research phase with small scale laboratory demonstrations of bandwidths of up to 2 5 Tbit s over a single light path 4 2 5 1 6 Code division multiplexing Code division multiplexing CDM or spread spectrum is a class of techniques where several channels simultaneously share the same frequency spectrum and this spectral bandwidth is much higher than the bit rate or symbol rate One form is frequency hopping another is direct sequence spread spectrum In the latter case each channel transmits its bits as a coded channel specific sequence of pulses called chips Number of chips per bit or chips per symbol is the spreading factor This coded transmission typically is accomplished by transmitting a unique time dependent series of short pulses which are placed within chip times within the larger bit time All channels each with a different code can be transmitted on the same fiber or radio channel or other medium and asynchronously demultiplexed Advantages over conventional techniques are that variable bandwidth is possible just as in statistical 22 multiplexing that the wide bandwidth allows poor signal to noise ratio accordi
62. y an analog technology FDM achieves the combining of several signals into one medium by sending signals in several distinct frequency ranges over a single medium Schcatrblnder Ip B E O Maa Signal 1 Signal 2 10 20 kHz Signal 3 00 S00 Hz Figure 2 11 Frequency Division Multiplexing 20 One of FDM s most common applications is the old traditional radio and television broadcasting from terrestrial mobile or satellite stations using the natural atmosphere of Earth or the cable television Only one cable reaches a customer s residential area but the service provider can send multiple television channels or signals simultaneously over that cable to all subscribers without interference Receivers must tune to the appropriate frequency channel to access the desired signal 1 A variant technology called wavelength division multiplexing WDM is used in optical communications 2 5 1 3 Time division multiplexing Time division multiplexing TDM is a digital or in rare cases analog technology which uses time instead of space or frequency to separate the different data streams TDM involves sequencing groups of a few bits or bytes from each individual input stream one after the other and in such a way that they can be associated with the appropriate receiver If done sufficiently quickly the receiving devices will not detect that some of the circuit time was used to serve another logical communication path Cons
63. zed Signal 27 amplitude Figure 3 3 Quantization 3 1 3 Reconstruction Reconstruction is the process of creating an analog voltage from samples A digital to analog converter takes a series of binary numbers and recreates the voltage levels that correspond to that binary number Then this signal is filtered by a lowpass filter This process is analogous to interpolating between points on a graph but it can be shown that under certain conditions the original analog signal can be reconstructed exactly from its samples The reconstruction is an approximation to the original analog signal 3 1 4 Aliasing Due to violation of the Nyquist Shannon sampling theory during sampling the base band spectrum of the sampled signal is mirrored to every multifold of the sampling frequency These mirrored spectra are called alias The signal spectrum reaches farther than half the sampling frequency base band spectrum and aliases touch each other and the base band spectrum gets superimposed by the first alias soectrum The easiest way to prevent aliasing is the application of a steep sloped low pass filter with half the sampling frequency before the conversion Aliasing can be avoided by keeping Fs gt 2Fmax 28 Figure 3 4 Aliasing 3 1 5 Nyquist Sampling Rate The Nyquist Sampling Rate is the lowest sampling rate that can be used without having aliasing The sampling rate for an analog signal must be at least two times the bandwidth of the signal

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