Product Review Column from QST Magazine
Contents
1. 4 2 0 2 Frequency Offset kHz Figure 1 Worst case spectral display of the unmodified IC 756 transmitter during two tone intermodulation distortion IMD testing at 28 350 MHz The worst case third order product is about 24 dB below PEP output and the worst case fifth order product is about 34 dB down The transceiver was being operated at 100 W output See text for additional details width is currently selected at each IF Everyone also liked the fact that as you manipulate the concentric twin passband tun ing TWIN PBT controls on the front panel a handy passband width graphic shows you the relative IF bandwidth and shift But one of this radio s very best at tributes is the ease of access to user settable adjustments or menus On some more expensive radios these settings are rel egated to separate complex nonintuitive menu systems that confound the user and require spending hours with the manual Not so with the IC 756 In fact getting to the plain language menus was so easy many users were able to tailor user settable parameters without referring to the book Thank you ICOM In fact most users didn t need the manual at all to operate the entire radio Shades of the IC 781 a horizontal row of Function keys F1 through F5 is below the LCD s2. ently switch to the second antenna port in stead of the receiving antenna however The radio s two preamps and three lev els of attenuation also elicited praise for their versatility So did the inclusion of ATX transmit incremental tuning You can clear RIT while transmitting but the knob s pointer might be heading in just about any direction when you do The ease of operating split drew starkly contrasting opinions Some ops had no problems with which buttons to push but others found the user interface confusing ICOM combines the typical A B and A B functions into a single CHANGE button which serves both purposes depending on how long you hold it in This befuddled some ops Most ops also would have pre ferred a more prominent means of indicat ing which VFO was set for transmit The IC 756 transmitter did not fare as well as we d hoped After the IC 756 served ably during the ARRL International DX CW Contest we received some troubling reports that its CW signal was particularly noisy ARRL Lab tests showed that CW sidebands did indeed extend beyond the bounds of reasonable expectation We tested two IC 756s plus several other ICOM and non ICOM radios Lab testing determined that at 2 kHz away from the signal on the worst case low side the CW sidebands of our IC 756 were 13 dB worse than those of an IC 706 and 7 dB worse than those of an IC 765 At 10 kHz away the CW sidebands were 14 dB worse than those
3. 1351 Hz LSB INTER 346 2396 Hz 2050 Hz LSB W 83 2537 Hz 2454 Hz USB N 838 2185 Hz 1347 Hz USB INTER 540 2545 Hz 2005 Hz USB W 70 2777 Hz 2707 Hz AM INTER 42 1185 Hz 1143 Hz AM W 42 2410 Hz 2368 Hz 121 dB 121 dB 230 dB At threshold SSB 14 2 MHz 0 52 uV FM 29 MHz 0 46 uV 1 0 MHz S9 88 0 uV 14 MHz 65 uV 2 1 W at 10 THD into an 4 Q load 590 mV into a 600 Q load S9 signal NOTE All dynamic range measurements were taken using the ARRL Lab standard spacing of 20 kHz Measurement was noise limited at value shown tThird order intercept points were determined using S5 reference arrow buttons lt and gt These can be used to tune the radio one tuning step at a time for each button press If you hold either of these buttons in the radio will tune up gt or down lt the band These buttons select the memory channel in memory mode Another series of buttons above the tuning knob allow you to select more functions The BANDWIDTH button selects one of four IF filters narrow intermediate wide and auxiliary AGC selects the fast or slow AGC action or turns it off completely TUNING RATE selects 10Hz 100 Hz or 1 kHz tuning steps The CHANNEL and FREQ buttons switch between the VFO and 200 memory channels more on this later There is also a button to turn on what JRC calls its exalted carrier selectable sideband ECSS feature which appears to be a synchronous detecti
4. and on a very busy band everything gsf May 1997 65 Reference Level 60 dBc Hz Vertical Scale dBc Hz Reference Level 60 dBc Hz Vertical Scale dBc Hz 4 6 8 10 12 14 Figure 4 Worst case tested HF spectral display of the unmodified IC 756 transmitter output composite noise testing at 3 5 MHz Power output is 100 W The carrier off the left edge of the plot is not shown This plot shows composite transmitted noise 2 to 22 kHz from the carrier starts to look like choppy seas from shore to shore On the other hand like the similar feature on the IC 706 spectrum scope should prove to be a great help in checking out more quiet bands like 6 meters which has been less than busy of late Using the spectrum scope you can quickly spot other activity on the band while parked on the calling frequency although the signals will have to be substantial to show up as much more than little blips on the horizon One VHF op suggested the spectrum scope would make it easier to avoid the trouble some big signal stations on the band DSP Highlights The IC 756 borrows heavily from the IC 775DSP for its DSP features espe cially in the superb implementation of its noise reduction NR feature which earned our praise in the IC 775DSP review see Product Review QST Jan 96 Like its big brother the 775DS
5. selecting frequency and memory channel scan features and activating the 20 dB attenuator Below the mode buttons are controls for setting the blanking level of the twin noise blankers a welcome feature The noise blankers were quite effective Also below the mode buttons are the bandwidth control BWC new with this model passband shift PBS also new squelch variable notch position and RF gain The main tuning knob is large with an uncalibrated analog apron It has the now commonplace finger sized depression to make rapid spinning easy The rubberized textured grip has a nice feel Just above the main tuning knob are two Minimum discernible signal MDS NARROW 1000 Hz IF filter 180 KHz 133 dBm 500 kHz 134 dBm 1 0 MHz 134 dBm 3 5 MHz 138 dBm 14 MHz 135 dBm 28 MHz 136 dBm AM WIDE IF filter test signal modulated 30 witha 1 kHz tone 10 dB S N N 1 MHz 0 58 uV 3 8 MHz 0 46 uV FM 12 dB SINAD 29 MHz 0 3 uV CW mode narrow 1000 Hz IF filter 1 0 MHz 121 dB 3 5 MHz 122 dB 14 MHz 118 dB CW mode dynamic range and third order intercept point narrow 1000 Hz filter IF filter Frequency Dynamic MHz Range dB 1 0 91 3 5 94 14 94 73 dBm 29 MHz 62 dB 29 MHz 65 dB Intercept point dBm t 6 3 4 3 5 2 Range at 6 dB points bandwidth CW N 47 1195 Hz 1148 Hz CW INTER 64 1701 Hz 1637 Hz CW W 106 2432 Hz 2326 Hz LSB N 825 2176 Hz
6. 10 15 14 14 35 6 9 7 5 9 9 10 5 13 9 14 5 17 9 18 5 20 9 21 5 18 068 18 168 21 21 45 24 89 24 99 28 29 7 24 4 25 1 28 30 50 54 MHz 50 54 MHz Modes of operation USB LSB CW AM FM RTTY As specified Power requirement Receive 2 7 A max audio transmit Receive 2 3 A max vol no signal transmit 17 9 A tested at 13 8 V 20 A max 13 8V 415 Size height width depth 4 4x13 6x11 4 inches weight 23 pounds Receiver Receiver Dynamic Testing SSB CW sensitivity bandwidth not specified Minimum discernible signal MDS 500 Hz IF filters at 10 dB S N 1 8 30 MHz preamp 1 on 0 16 uV 9 MHz and 455 kHz 50 54 MHz preamp 2 on 0 13 pV Freq Preamp off Preamp 1 Preamp 2 s 1 0 MHz 124 dBm n a n a 3 5 MHz 134 dBm 139 dBm 139 dBm 14 MHz 134 dBm 139 dBm 142 dBm 50 MHz 131 dBm 139 dBm 141 dBm AM sensitivity preamp on bandwidth not specified 10 dB S N N signal 30 modulated with a 1 kHz tone AM N filter 10 dB S N 0 5 kHz to 1 8 MHz 13 uV 1 8 30 MHz 1 0 MHz 3 05 uV 3 8 MHz preamp off 1 07 uV preamp 1 on 2 uV preamp 1 or 2 on 0 65 uV 50 2 MHz preamp off 1 43 uV preamp 1 on 0 62 uV preamp 2 on 0 42 uV FM sensitivity 12 dB SINAD 28 29 MHz preamp 1 on For 12 dB SINAD FM N mode 0 5 uV 50 54 MHz preamp 2 on 0 32 uV 29 MHz preamp off 0 58 uV preamp 1 on 0 24 uV preamp 2 on 0 19 uV 52 MHz preamp off 0 77 uV preamp 1 on 0 30 uV preamp 2 on 0 22 uV Bl
7. Q 2 1 W at 10 THD into 8 Q IF audio response Not specified Range at 6 dB points bandwidth CW N both 500 Hz IF filters 348 813 Hz 465 Hz CW W 2 4 and 2 8 kHz IF filters 216 2717 Hz 2501 Hz USB N 2 4 and 2 8 kHz IF filters 239 2765 Hz 2526 Hz LSB N 2 4 and 2 8 kHz IF filters 218 2720 Hz 2502 Hz Notch filter depth Not specified 250 dB Spurious and image rejection Greater than 70 dB IF rejection 2120 dB image rejection 120 dB Transmitter Transmitter Dynamic Testing Power output SSB CW RTTY FM 2 100 W As specified AM 1 40 W continuously adjustable in all modes Spurious emission supression 50 dB HF bands 60 dB 55 dB or greater on HF greater than 60 dB on 50 MHz Meets FCC require 50 MHz band ments for equipment in its power output class and frequency range SSB carrier suppression 40 dB 55 dB or greater Undesired sideband suppression 55 dB As specified Third order intermodulation distortion IMD See Figures 1 and 2 products Not specified Composite transmitted noise Not specified See Figures 4 and 5 Note Unless noted otherwise all dynamic range measurements were taken at the ARRL Lab standard spacing of 20 kHz Measurement was noise limited at the value indicated t Third order intercept point was determined using S5 reference 64 May1997 gst Reference Level 0 dB PEP Reference Level 0 dB PEP
8. admirably with the big boys in several per formance spheres In terms of DSP equipped radios the 756 is intended for more mainstream users During the review we encountered some transmitter related problems that ICOM has agreed to correct in future production units We ll discuss these issues later in the review Feature Highlights The first thing you need to do with the IC 756 is to get past the LCD display win dow Otherwise you could overlook the radio s other assets These include such niceties as an automatic antenna tuner works on 6 meters dualwatch dual an tenna ports a receive antenna port for a Beverage EWE or other antenna memory keyer front panel adjustable CW pitch control and tracking sidetone triple band stacking registers twin passband tuning at the 9 MHz IF and more A lot of these are features traditionally included on ICOM s higher priced radios so it was great to find them on the more modestly priced IC 756 You ll also find a generous array of memo ries and scanning features 99 memories plus 2 priority memories alphanumeric memory naming up to 10 characters 5 or Gall oan Be ee Ea aali TRANSMIT PHONES TUNER MONTOR NB wR AF RF SOL BAL O NA Aa amp BLEC KEY 6 E 10 memo pads and four types of scanning The IC 756 lets you view the contents of nine memory channels at a time or scroll through them all via its memory channel screen St
9. darn near everything Save for the nearby analog multifunction meter and some colored LEDs on the front panel the screen can tell you everything else you need to know The meter seems a quaint retro touch on a radio featuring a modern digital LCD window and readout But several users felt more comfortable with the real meter Like the hands on an analog clock one reviewer explained In the LCD window you ll find infor mation on what frequency each of the two VFOs is tuned to along with indicators to tell youif such features as split or dualwatch are active more on dualwatch a bit later The frequency display upper is in bold nu merals while the sub band frequency lower is in slightly smaller outlined nu merals It s possible to set the radio to dis play resolution down to 1 Hz A handy 24 hour digital clock with bat tery backup is displayed in the upper right hand corner of the screen Other displayed information includes which VFO you re transmitting on main or sub along with numerical memory information memory number and stored frequency One nice touch appears at the top of the screen where the display clearly shows which filter band gsf May 1997 63 Table 1 ICOM IC 756 serial no 01238 Manufacturer s Claimed Specifications Measured in the ARRL Lab Frequency coverage Receive 30 kHz to 60 MHz Receive as specified transmit 1 8 2 3 4 4 1 transmit 1 8 2 3 5 4 7 7 3 10 1
10. for the antenna wire and ground A DC OUT jack supplies 10 8 V dc at up to 30 mA to run a station accessory Audio is available on the LINE OUT and EXTernal SPeaker jacks For RTTY operators there are jacks for the MARK and SPACE signals which can be used with an oscilloscope as a tuning indicator with the optional RTTY demodulator installed The SCAN HOLD jack provides a way for you to temporarily stop the scan operation and the MUTE JACK allows you to disable the receiver by grounding this line This is especially handy if you want to use the 535 in your ham station with a separate transmitter or transceiver The AF IF and RF stages are muted and the 20 dB attenuator is activated and JRC says this provides more than 120 dB of antenna isolation so you should be able to monitor your transmitted signal off the air in the mute position The NRD 525 also had an auxiliary RF gain pot that you could adjust to set receiving level while muted The NRD 535D doesn t have that nor does it offer a transmitter sidetone input connection as the 525 did Also there is no provision to connect the VFO signals between the 535 and a transceiver or transmitter not even a JRC transceiver A means to connect this receiver to my transceiver so I could use either VFO or operate split or dual receive would have been a useful addition There are three terminals for use with the timer feature which makes it possible to operate a tape recorder or
11. its tuning range AM sensitivity was a bit better than what we measured on the 525 Dynamic range is an important consideration for any receiver especially if you re listening in the highly populated areas of the spectrum Two tone third order IMD dynamic range numbers were com parable to those of the earlier NRD 525 so were third order intercept figures Especially remarkable was the in band audio IMD performance of the NRD 535 Lab tests showed that in band IMD was mini mal That obviously contributed to the clean crisp audio we noted The NRD 535 offers a variable IF notch filter that minimizes but might not eliminate interfering signals especially strong ones It s useful but it s not as effective as the newer DSP filters and our Lab tests showed that the notch filter missed its specified 40 dB depth by 10 dB You can listen a bit outside the radio s specified 0 1 to 30 MHz tuning range an undocumented bonus Like the earlier 7525 our NRD 535D would tune to 0 00 kHz but many spurs were evident below the 100 kHz lower tuning limit and we found that noise increased drama tically below 20 kHz In addition sensitivity began to drop off as we tuned below 100 kHz to around 93 dBm at 20 kHz Sweeping Scanning and Memories There are two types of scanning possible with this radio JRC refers to the process of searching through the memories as scanning You set up this mode by setting the start and s
12. most of the bottom of the radio Across the width running front to back are nine slots for daughter boards The optional units plug into empty slots on the mother board so options installation should be quite simple More Operating Impressions The JRC NRD 535D was built with serious shortwave listeners in mind but hams who also enjoy just listening or who need a second receiver also will appreciate its assets Many of the features are handy for cruising the shortwave bands and some of them really enhance your operating pleasure on the ham bands During the review period I was playing with some slow scan TV equipment I noticed that a bit of interference while I was receiving a picture could greatly degrade the received picture quality The older transceiver I was using had limited filtering options When I connected the 535 tothe SSTV scan converter however I could select the INTERmediate 1 8 kHz or NARROW 1 kHz filter you can select any filter in any mode With the INTER setting I could further reduce the bandwidth with the bandwidth control BWC The passband shift PBS control also helped cut interference While this was possibly not as effective as a good DSP filter I was definitely able to receive better pictures on SSTV By the way the BWC really came in handy on SSB voice operation too While the stock 1 kHz NARROW filter isn t quite narrow enough for CW reception on a crowded band with the INTE
13. of an IC 706 and 24 dB worse than those of an IC 765 Lab Supervisor Ed Hare KAICV predicted that keying sidebands of this level would have an adverse impact on other users of the band We discussed this issue with ICOM and the manufacturer subsequently sent us another IC 756 that had been modified to correct the wide CW signal problem We found the modified radio to be vastly superior in this regard While not as clean as an IC 765 we d tested the IC 756 s CW spectral display was slightly better than that of the IC 706 In addition the keying waveform was much cleaner on the modified radio and showed none of the rough edges we d noticed in the first two units we d tested see Figure 3 Our Expanded Test Report on the IC 756 includes graphs of the radio s keying sidebands and those of other radios for comparison Ed Judging from the two tone transmit IMD plots we took see Figures 1 and 2 the IC 756 might sound wide on SSB on some bands The transceiver s worst case transmit two tone IMD on MF HF was 10 meters where testing not only revealed mediocre suppression of third and fifth order products down 24 and 34 dB respectively but showed subsequent higher order products persisting at rather high levels not until the 13th order do IMD products drop to 55 dB These are the culprits that cause undesirable splatter That said we d like to point out that IMD performance on 160 through 20 m
14. other device for unattended recording This can be set up to connect one set of terminals when the timer is on and another set when the timer is off You can also configure the operation of the timer off contacts to turn on only when the squelch threshold is broken The NRD 535D back panel also has an RS 232C port When it s connected to a computer loaded with appropriate software 2 you can control just about every radio operation through this port Among other things you can set the receive frequency select the bandwidth by specifying the IF filter and adjusting the bandwidth control set the clock and set RTTY parameters from your computer You can also read the various receive parameters to determine the radio operating conditions from a remote location There s a list of commands in the 70 May1997 gst Instruction Manual but the manual skimps on how to actually get computer control up and running More Operating Controls Sixteen of the radio s default CPU parameters can be changed via menus to suit your operating preferences Some of the parameters seem rather esoteric while others are more vital I can t get too excited about being able to make the colon in the time display blink or remain steady but I sure do like the ease with which I can change the CW offset over a range of 5000 Hz If you prefer an S meter display with a needle indicator rather than a bar you can make that change in the menu If
15. subjects including how to install options Step by step items labeled CONVENIENT point out how you might use dualwatch for example Other text boxes labeled PRACTICAL EXAMPLE illustrate such things as how to initiate split opera tion Overall a generous combination of diagrams drawings and succinct text con tribute to a no nonsense approach Conclusions One op who spent some time with the IC 756 summed things up this way General purpose operators or DXpeditioners will find that the IC 756 offers an abundance of features to cope with what they find on the bands The tools are there to help eliminate QRM and dig out the weak ones The small size is great for anyone who needs to travel with a radio of course they would have to bring along a suitable power supply It even has a carrying handle In the final analysis the review team got good audio reports liked the user interface for the most part and found the layout of the front panel controls to be clear and uncomplicated Thanks go to the following hams who contributed to this review Randy Thomp son K5ZD Dave Sumner K1ZZ Linda Sumner KAIZD Mark Wilson K1RO Peter Budnik KBIHY Emil Pocock W3EP Rick Lindquist NIRL and Mike Gruber W1DG and Ed Hare KAICV of the ARRL Lab Manufacturer ICOM America Inc 2830 116th Ave NE Bellevue WA 98004 tel 206 454 8155 fax 206 454 1509 WWW _shttp www icomamerica com Manufacturer s suggested ret
16. used channel number If you change memory channels and then go back to the original you then will have the settings that were previously stored with that channel But when you switch back to VFO operation you will have the same frequency and settings as the memory channel The radio won t save the frequency and settings you had when you were in VFO operation and there s no way to retrieve them unless of course you remembered to store them before switching to memory operation The process of storing data to memory seemed a bit more complicated than necessary If you want to save the frequency and operating conditions on the display to a memory channel whether you are in VFO or memory operation you first press the MEMO button This makes the LED indica tor on the CHANNEL button flash At this point you must press the ENT KHz button and the CH indicator on the display also will flash Now you must enter the desired channel number with the numeric keypad and press ENT KHz again At this point all the flashing stops and the desired frequency and settings are saved Each memory is completely tunable and you can change all the settings But if you want to save the changes you will have to go through the memory store procedure before you change memory channels The Instruction Manual Except for a lack of information regarding computer control the 50 page Instruction Manual covers all other aspects of using the radio and e
17. P the 756 uses DSP to equalize transmit audio as well as for its automatic IF notch filter audio peak filter APF and phase shift network PSN modulation and demodulation Most users felt the noise reduction was among the radio s finest DSP features on receive but the usable range on the NR control is very restricted About one quarter turn is as much as you ll ever need to quiet things down It even worked on atmospheric noise and it did not exhibit that annoying hollow sound we ve noticed on some other DSP NR systems One user liked the NR on the 756 better than the one on his ac claimed outboard box explaining how sta tions popped intelligibly out of the noise when he turned the pot We got contrasting viewpoints on the audio peak filter APF Opinions ranged from useless to worked like magic Consensus was that it was great for beefing up solitary CW signals like beacons and for punching up one signal among a small group but it was less effective on a busy 66 May1997 QS 18 20 4 6 Frequency Sweep 2 to 22 kHz from Carrier the carrier band APF offers three bandwidths On FM it works as a tone control The DSP automatic notch works well to eliminate those pesky heterodynes that crop up on the HF bands that are shared with broadcasters in other parts of the world Anyone who s operated 40 meter SSB at night in the Northeast will appreci ate this feature But one CW op said that la
18. Product Review Column from QST Magazine May 1997 ICOM IC 756 MF HF VHF Transceiver Japan Radio Co NRD 535D HF Receiver Copyright 1997 by the American Radio Relay League Inc All rights reserved ICOM IC 756 MF HF V HF Transceiver By Glenn Swanson KBIGW Educational Programs Coordinator Honey they shrunk the IC 781 is what some ops will exclaim when they see the IC 756 It s an easy comparison and one ICOM ad even calls it a radio for the ham who s always wanted an IC 781 Features like the prominent front panel LCD display screen on the 756 certainly hearken back to its elder sibling the IC 781 with its conspicuous CRT display As in the IC 781 the IC 756 offers such features as dualwatch and Spectrum Scope But in several respects this is a different radio maybe better when you consider its price and performance the inclusion of DSP and an intuitive menu system At least a few reviewers were surprised to find a package closer in dimensions to the IC 736 the radio it replaces in ICOM s product line But the IC 756 capitalizes on and even improves on some of the best features of its predecessors and does so with style Let s face it that LCD screen is just plain sexy The easily accessible menus spectrum scope and the inclusion of 6 meters are icing on the cake In the greater scheme of things the IC 756 is a notch down from higher end offerings in terms of price but competes
19. Rmediate filter you can reduce the IF bandwidth to 500 Hz using the bandwidth control I set the CW offset to 500 Hz and found it was quite pleasant to copy CW with this receiver One nit the AGC has fast slow and off positions but only one button to step through the choices This means at some point you ll have to pass through the off position and the audio will get quite loud So take off your headphones or turn down the volume first Do I Need One Hams who still roll their own transmitters use older transmitters especially for AM or just need a backup station receiver might find the NRD 535 an able companion In terms of receiver performance the NRD 535D compares favorably with some of the transceivers popular with DXers and contesters and acquits itself quite well on the amateur bands JRC says it plans to continue to offer the NRD 535D for the foreseeable future and serious listeners would do well to give the NRD 535D serious consideration Manufacturer Japan Radio Co Ltd 430 Park Ave New York NY 10022 tel 212 355 1180 fax 212 319 5227 Manu facturer s suggested retail price NRD 535D receiver 2029 NVA 319 external speaker 210 high stability crystal oscillator unit CGD 135 87 RTTY demodulator unit CMH S530 118 Notes 1Gilfer Shortwave 52 Park Ave Park Ridge NJ 07656 orders 800 445 3371 800 GILFER 1 tel 201 391 7887 fax 201 391 7433 2DOS software from TRS Consultants is ava
20. ail prices IC 756 2760 PS 85 dc power supply 325 SM 20 desktop microphone 248 9 MHz IF filters FL 223 1 9 kHz 84 FL 100 500 Hz 106 FL 232 350 Hz 90 FL 101 250 Hz 106 455 kHz IF filters FL 222 1 8kHz 199 FL 52A 500 Hz 196 FL 53A 250 Hz 196 CT 17 computer interface 135 Notes 1With many radios that offer a receive antenna port that remains in line while transmitting you ll need to protect the transceiver from adverse reactions by adding a device to iso late the rig from your own transmitted signal This station engineering issue may apply to those with receive antennas such as Bever ages or EWEs One solution is to wire a relay to switch the separate listening antenna con nection to ground or to at least isolate the antenna s feed line from your receiver dur ing transmit For a specific approach see Beverage Antennas There s More to Them Than Meets The Eye by Gary R Nichols KD9SV CQ Feb 97 2It might sound strange but a CW signal also has sidebands It makes more sense if you think of a CW signal simply as a carrier that s being modulated by a square wave on off keying Take a look at the keying envelope in Figure 3 Expanded Product Review Report Available The ARRL Laboratory offers a comprehensive test result report on the IC 756 that gives in depth detailed technical data on the transceiver s performance outlines our test methods and helps
21. andard accessories include a hand mike with UP and DN buttons a 9 2 foot long fused dc power cord spare fuses a 1 4 inch stereo type phone jack and large detailed block and schematic diagrams The Screen The LCD screen commands the black plastic face of the 756 One user com pared it to the screen on the ATM at her bank The screen appears dark when the radio is off but illuminates when you turn the radio on to reveal a light blue back ground with dark blue text numerals and graphics A thin unlighted black mask frames the screen and a clear plastic lens protects the flat LCD screen behind it The screen s illuminated area measures ap proximately four inches wide by three inches high about the same size as the IC 781 s CRT display BOTTOM LINE To invoke an automotive analogy if the IC 781 and IC 765 represent ICOM s high end race cars the IC 756 is the full featured family sedan that takes advantage of modern technology while aiming at the price and perfor mance needs of the general market Edited by Rick Lindquist N1RL Senior Assistant Technical Editor The LCD screen needed some warm up time to reach proper contrast We found the display could be easily seen up to 30 off dead center on either side Tinkering with the contrast levels can make it easier to see It looks best when you re directly in front of it however What information does the screen con vey The answer is
22. ange with preamp 2 kicked in was 12 dB better than the 736 That s something you ll be glad of when you re sorting through a band opening with its mixture of very loud and very weak signals close together in frequency Dualwatch is a nice touch Six meter fans for example will appreciate the ability to monitor both the 50 110 MHz and 50 125 MHzcalling frequencies at the same time a big plus But the sub band receiver is strictly for in band use and it won t let you listen to two signals on different bands say on 6 and 10 meters at the same time so you can keep one ear on the 10 meter liaison frequency For more details on how dualwatch works see Product Review OST Jan 96 p 67 One primarily VHF op enthused about the noise blanker saying that it worked as well as the noise blanker any rig I have tried and better than most He found that it worked great for the intended purpose of minimizing pulse type noise but it didn t make much of a dent in troublesome noise emanating from a nearby high tension line He said both noise sources cooperated by being espe cially noisy during the review period For the most part our review team liked the front panel selectable separate receive antenna input which served to connect a Beverage antenna for contest use on the low bands The other manufacturers could learn something from ICOM one user said A few ops found it was too easy to inadvert
23. ar with the earlier model will find that although the front panel has a more modern look to it the control layout is very similar We reviewed the deluxe version NRD 535D Gilfer Shortwave offers a souped up NRD 535GS Details are on the Gilfer Web page at http www gilfer com 68 May1997 QS jrc535gs htm The 535D includes the bandwidth control module the exalted carrier selectable sideband ECSS unit and the narrow 1 kHz filter THE BOTTOM LINE The JRC NRD 535D is a proven performer among BC and SWLers and it could be a great complement to the ham shack too It s loaded with fea tures and a pleasure to listen to NRD S35D HF RECEIVER AF GAIN Tone From the Front If you squint the 535D resembles JRC s JST 245 amateur transceiver see Product Review QST Sep 95 It s a good looking radio with smooth lines and plenty of nice sized knobs and buttons to play with But not too many There are no concentric controls either something that those with big fingers might appreciate The top left side of the radio includes the fluorescent display with frequency mode bandwidth S meter and other operational information Below the display are mode buttons for Table 2 Japan Radio Corp NRD 535 Communications Receiver serial number 68926 Manufacturer s Specifications Frequency coverage 0 1 30 MHz Modes of operation AM USB LSB CW RTTY FAX and NFM Power requireme
24. ather have had individual labels on each jack or connector instead of the single plate in the middle of the panel The IC 756 has no transverter port Computer control is possible via the RE MOTE jack but you ll need the optional CT 17 CI V level converter On The Air Our IC 756 hit the ground running in large part because the steep learning curve encountered with some new transceivers simply didn t exist with the IC 756 The radio put in an appearance in several contests including the ARRL International DX Contest CW and SSB and the CQ 160 Meter SSB Contest It also got used on 10 and 6 meters and for casual rag chewing on HF CW and SSB An internal fan just behind the front panel kept the radio cool even during long contest operation We never heard it Same for the automatic antenna tuner which uses a combination of motors and relays Our review team found the receiver per formance above average Our unit had the optional 250 Hz CW filter in the 9 MHz IF and an optional 500 Hz CW filter in the 455 kHz IF Experienced CW operators said this yielded a receiver with sufficient selectivity for all but the most demanding circum stances Users felt the twin passband tuning gave an added edge in troublesome QRM situations although one op who used the radio for SSB said the twin PBT was not a substitute for the narrow filters on that mode The CW PITCH control gives you suffi cient latitude to suit nearly all tastes
25. ck of an equally effective manual notch made it half a feature since an auto notch is useless on CW The auto notch is outside the AGC loop so you ll still see the inter fering signal on your S meter and on the spectrum scope even though you can t hear it and it can still affect your receiver s front end The ability to tweak transmit audio to taste was a real plus Everyone s voice is different and this DSP feature bursts through the old one size fits all mental ity letting you customize the equalization for your voice Users liked being able to use the transmit audio treble and bass settings quickly accessible via the user friendly menu to optimize transmit audio the way they needed it from really punchy contest audio to pleasant con versation quality audio The built in monitor lets you hear your own signal The IC 756 follows up its fine DSP au dio equalization system with AF level speech processing While you can use the ALC scale on the multifunction meter to set a maximum level using one of the little stem controls on the front panel apron you really have no idea how much or how little compression ie how many dB you re cranking in IF Filters The IC 756 can be equipped with up to two optional narrow IF filters one each in the 9 MHz and 455 kHz IFs In other words you must choose between either SSB or CW filters This is one drawback in what is otherwise a
26. creen and on screen legends above each key indicate the key s function depending on the menu ICOM calls it a set mode selected For example contrast and S meter backlighting controls allow you to adjust these levels to your liking Just press F5 EXIT until you reach set mode Then choose F2 Display Set and use the F1 and F2 keys now defined as up and down ar rows and spin the VFO knob to adjust LCD contrast brightness and the backlighting levels for the S meter and push buttons Each adjustment has a little percentage scale which makes it easier to remember your settings On menus where it s ap propriate one button restores default DEF settings When you re done press F5 to EXIT the set mode A vertical row of seven multifunction buttons is arranged down the left hand side of the display window Just like the Func tion buttons a corresponding column of on screen labels conveys the role each button 4 2 0 2 pene ia 1E MESAS Tt ji Figure 3 CW keying waveform for the unmodified IC 756 showing the first two dits in full break in QSK mode The equivalent keying speed is 60 WPM The upper trace is the actual key closure the lower trace is the RF envelope Horizontal divisions are 10 ms The transceiver was being operated at 100 W output at 14 2 MHz Note that the first dit is somewhat shortened This is much less evident in semi break in mode plays in a given set mode For exa
27. eters was on a par with other transceivers we ve seen lately and higher order products ie beyond fifth order were at or below 60 dB in most cases Transmit IMD performance started to degrade at 17 meters and got progressively worse through 10 meters not only with respect to third order numbers but to higher order products Transmit IMD performance of the IC 756 was much worse than that of the earlier IC 738 see Product Review QST Apr 95 which had worst case third and fifth order products of 40 dB Like the IC 738 the IC 756 uses bipolar transistors in the PA as opposed to power MOSFETs On the other hand 6 meter transmit IMD performance of the IC 756 was notably better than that of the predecessor IC 736 but higher order IMD products do not drop below 40 dB until the 15th order On bands with these levels of transmit IMD an amplifier could tend to exacerbate the problem on the air It was interesting to note that the IC 756 that ICOM had modified to fix the CW sidebands problem also exhibited far superior reduction of higher order transmit IMD products While the third and fifth order products on 10 meters and 6 meters were comparable to those of the other two IC 756s we d tested the higher order products on those bands were much less evident on the modified radio ICOM expressed its appreciation to the ARRL for its findings with regard to the performance of the IC 756 and said We continually refi
28. even for one reviewer who likes to copy his code at a pitch of 280 Hz In band audio IMD something we ve criticized ICOM radios for in past product reviews was not a problem with the IC 756 Receiver audio quality was judged to be on a par with other radios in its price class The ARRL Lab reported third order products improved by 14 dB over the unmodified IC 775DSP in the AGC fast setting that we looked at last year see Product Review QST Jan 1996 The internal automatic antenna tuner is active on all bands and works in receive as well as transmit Using it on receive certainly raised the radio s second order intercept point see Table 1 from 48 6 dBm to a very respectable 83 5 dBm with the preamp off Second order dynamic range improved by approximately 17 dB with the preamp off when using the built in antenna tuner during receive Unfortunately we could not will the 6 meter band to open so we were unable to gauge the radio s performance during a busy day on the magic band The trans ceiver tunes below 50 MHz so the 6 meter DXer can check for those overseas TV car riers that alert ops to openings If the Lab numbers see Table 1 are any indication the IC 756 should perform very well on 6 meters For starters it should be able to hear those weak signals receiver sensitiv ity on SSB and CW was comparable to the IC 736 141 dBm with preamp 2 turned on Two tone third order IMD dynamic r
29. flexible and generally 8 10 12 14 16 18 20 22 Frequency Sweep 2 to 22 kHz from Carrier Figure 5 Spectral display of the unmodified IC 756 transmitter output during composite noise testing at 50 2 MHz Power output is 100 W The carrier off the left edge of the plot is not shown This plot shows composite transmitted noise 2 to 22 kHz from well thought out radio Optional CW and data mode filters of fering bandwidths of 250 350 or 500 Hz are available for both IFs For SSB there s an optional 1 9 kHz filter in the 9 MHz slot and a 1 8 kHz filter for the 455 kHz IF It s a shame you can t add both types at the same time Bringing narrow IF filter s into play is as easy as making other menu choices We felt this filter selection scheme was a de cided and welcome improvement over the LED push button based filter selection system employed in the IC 775DSP while also recognizing that the 775DSP also offers more filter choices The Flip Side The rear panel on the 756 is not a separate panel at all It s actually part of a 4 inch high cast aluminum framework that surrounds the radio s innards save for the front panel which is mounted in front of the aluminum chassis Rear panel connec tions for all the usual suspects are there plus the additional receive antenna port and a straight key jack and two DIN plugs fora variety of external connections Most users would r
30. il able from Gilfer Shortwave see note 1 above Order item T03601 59 95 plus 3 shipping and handling Expanded Product Review Report Available The ARRL Laboratory offers a comprehensive test result report on the JRC NRD 535D receiver that gives in depth detailed technical data on the receiver s performance outlines our test methods and helps you interpret the numbers and charts Reports are 7 50 for ARRL members and 12 50 for nonmembers postpaid Request the NRD 535D Test Result Report from the ARRL Techni cal Department 225 Main St Newington CT 06111 personal checks accepted For credit card orders only call 860 594 0278 mst Oot May 1997 71
31. mple a button next to the AGC label lets you toggle between fast middle and slow AGC set tings holding it in momentarily turns off the AGC The AGC action was flawless Another button selects ANT 1 or ANT 2 holding it in momentarily in either position lets you select a separate receiving antenna more on this later Other items the user can tweak give you the ability to tailor your transmit audio this is done using DSP You also can set a timer to turn the radio on or off at a preset time or set the radio to beep at you when you go out of band You can also make adjustments for CW sidetone level Some hard core CW buffs might not want to hear this but you don t even need to know the code to pro gram the memory keyer Using the keyer set mode you can change the plain lan Frequency Offset kHz Figure 2 Spectral display of the unmodified IC 756 transmitter during two tone intermodulation distortion IMD testing at 50 2 MHz The worst 37 dB below PEP output and the worst case fifth order product is approximately 33 dB down The transceiver was being operated at 100 W output See text for additional details case third order product is approximately guage messages for each of the keyer s four 55 character buffers to send whatever mes sages you need Programming the keyer requires a lot of button pushing however more than a few CW ops will balk at not being able to simply record their messages from their paddle
32. ne and update our products All production of the IC 756 from April 1 1997 will include changes made to improve the CW characteristics of the transceiver ICOM said the CW modification also would improve the transmit IMD performance Of considerably less importance were reports of choppy or clipped keying when using the internal keyer and full break in at speeds much more than 30 or 35 WPM The radio lets you change the dot to dash ratio but only very slightly and this made only minimal improvement Instruction Manual After all the hoopla that surrounded the introduction of the first transceivers with integrated DSP it s just a little curious that gsf May 1997 67 ICOM s Instruction Manual downplays DSP on the IC 756 ICOM s ads mention IF DSP but you d have to look very carefully to find the expression DSP any where in the Instruction Manual it s on the block diagram DSP is hardly pass but have we reached the point where there s no longer a need to point out that a radio has DSP At least one reviewer felt it would be nice if the manual contained a simple DSP next to each of the headings that describe DSP based features There were few complaints about what the manual does include however Op tional IF filter installation setup and op eration did involve a bit of jumping from page to page to find relevant information but the text offers pointers to pertinent pages for most
33. nts 100 120 220 240 V ac 10 12 16 V dc 13 8 V standard at approx 2 A Measured in ARRL Lab As specified with some usable sensitivity below specified lower limit As specified DC current drain 1 1 A max volume no signal tested at 13 8 V dc Lab testing conducted using 120 V ac Size HWD 5 2x13 2x11 5 inches weight 19 8 Ib CW SSB sensitivity 10 dB S N INTER filter 0 1 0 5 MHz 5 0 uV 93 dBm 0 5 1 6 MHz 2 0 uV 101 dBm 1 6 30 MHz 0 32 uV 117 dBm AM sensitivity 10 dB S N INTER filter 0 1 0 5 MHz 15 8 uV 0 5 1 6 MHz 6 3 uV 1 6 30 MHz 2 0 uV FM sensitivity 12 dB SINAD INTER IF filter 1 6 30 MHz 0 5 uV Blocking dynamic range Not specified Two tone third order IMD dynamic range 106 dB channel spacing not specified Second order intercept point Not specified FM adjacent channel selectivity Not specified Not specified FM two tone third order dynamic range IF audio response Not specified IF rejection 70 dB or better Image rejection 70 dB or better Notch attenuation 40 dB or greater Squelch sensitivity Not specified S meter sensitivity Not specified Audio output 1 W or greater at 10 distortion into an 4 Q load Line out RECORD level Not specified RTTY CW USB LSB AM FM and FAX When used with the FUNCTION button each mode button serves a second purpose such as selecting the display brightness controlling the clock and timer features
34. ocking dynamic range Not specified Blocking dynamic range 500 Hz filters at 9 MHz and 455 kHz preamp 1 on for 1 21 MHz preamp 2 on above 21 MHz Freq Preamp off Preamp on 1 0 MHz 135 dB n a 3 5 MHz 137 dB 132 dB 14 MHz 132 dB 128 dB 50 MHz 125 dB 118 dB Two tone third order IMD dynamic range Not specified Two tone third order IMD dynamic range 500 Hz IF filters at 9 MHz and 455 kHz preamp 1 for 1 21 MHz preamp 2 above 21 MHz Freq Preamp off Preamp on 1 0 MHz 95 dB n a 3 5 MHz 101 dB 101 dB 14 MHz 103 dB 100 dB 50 MHz 96 dB 94 dB Third order input intercept Not specified Preamp 1 for 1 0 21 MHz preamp 2 above 21 MHz t Freq Preamp off Preamp on 1 0 MHz 21 8 dBm n a 3 5 MHz 14 7 dBm 8 7 dBm 14 MHz 21 0 dBm 10 5 dBm 50 MHz 26 1 dBm 0 7 dBm Second order intercept point Not specified 14 MHz preamp off antenna tuner off 48 6 dBm antenna tuner on 83 5 dBm FM adjacent channel rejection Not specified At 20 kHz spacing 29 MHz preamp off 81 dB preamp 2 on 80 dB 52 MHz 67 dB preamp off 67 dB preamp 2 on FM two tone third order IMD dynamic range At 20 kHz spacing 29 MHz preamp off 73 dB preamp 2 on 72 dB Not specified 52 MHz preamp off 69 dB preamp 2 on 70 dB Squelch sensitivity SSB CW RTTY less than 5 6 uV At threshold FM 29 MHz preamp 2 on 0 07 uV FM less than 1 0 uV 50 2 MHz preamp 2 on 0 37 uV SSB 14 2 MHz preamp 1 on 0 98 uV Receiver audio output gt 2 W at 10 THD into 8
35. on scheme This reduces the garbling effects of selective fading of AM signals where the carrier frequency fades leaving only the sidebands The ECSS works quite well While in the ECSS mode you can choose the sideband farthest from an interfering signal to minimize the interference To use it you press the ECSS button and select USB or LSB as appropriate effectively removing the other sideband and carrier Compared with the standard AM mode on the radio we found slightly improved audio fidelity of AM signals even on the ham bands using ECSS Tuning can be a bit tricky when using this feature If you re not within 500 Hz of the desired carrier frequency before turning ECSS on or if the radio can t lock onto the carrier you will hear a loud squeal I found it easier to first tune in the signal in SSB mode perhaps because I have had more gst May 1997 69 experience tuning in SSB than AM The front panel also includes a numeric keypad for direct frequency entry and to set other options There are rotary AF GAIN and TONE controls too From the Back The rear panel has a full complement of connectors The radio has a built in ac power supply for 100 120 220 or 240 V ac input settable at the fuse holder but you can also power the radio from a 12 to 16 V dc supply capable of at least 2 A An antenna connects via an SO 239 50 Q connector or unbalanced high impedance 600 Q wire antenna push terminals
36. s One nice touch the keyer offers sequential QSO serial number ing The keyer speed range is approxi mately 6 47 WPM There are five little stem controls along the front panel s bottom apron These include adjustments for mike gain RF power compression level keyer speed and break in delay Unlike similar controls on the IC 781 you can t push these back in and out of sight And the Spectrum Scope While appealing at first blush the spec trum scope drew mixed opinions from our review team about its usefulness in the real world While the IC 756 spectrum scope looks similar to the one on the earlier IC 781 ICOM says it s implemented dif ferently The IC 756 spectrum scope has its own RF amplifier and AGC making it independent of the S meter and the RF gain control It is affected by the pre amps though One user said he found it interesting to watch the fading patterns on 40 meter HF broadcast stations one after noon especially noting the timing of the fades which differed from signal to signal But the same op and others found little use for the spectrum scope for contesting An other op called the spectrum scope kind of fun and suggested it was a handy tool for spotting band activity We found that the display requires a moderately strong signal S4 or so just to show up on the graph and a pretty hefty signal to really be seen The image does not refresh rapidly enough to catch signal splat ter
37. the main tuning knob rate of 1000 steps per revolution is too fast you can slow it down to only 250 steps per revolution If you want to eliminate the slight signal attenuation introduced by the receiver front end filters you can bypass them via a menu selection This may help you pull in that extremely weak signal but will also increase interference from strong signals over a fairly wide frequency range You probably wouldn t want to set and forget that one but it might prove valuable at times Circuit Features The NRD 535D is a triple conversion superheterodyne receiver with IFs of 70 455 MHz 455 kHz and 97 kHz For FM reception only the first two IFs are active The selectable filters are part of the second IF The WIDE filter has a 6 dB bandwidth of 6 kHz and the INTERmediate filter has a 6 dB bandwidth of 3 kHz You can narrow the effective bandwidth of both of these with the bandwidth control The BWC does not work in the NARROW filter position With no auxiliary filter installed the effective bandwidth is 12 kHz The 535 uses a phase locked loop and direct digital synthesis hybrid to control the operating frequency By the Numbers Tests in the ARRL Lab suggest this receiver should perform well see Table 2 As was the case in the 525 sensitivity in the NRD 535D is not reduced automatically in the vicinity of 1 MHz ie the AM standard broadcast band We found that sensitivity was fairly uniform across
38. top memory numbers and then hitting the RUN button There is no way to skip certain memory channels within the range you set the NRD 525 could not do this either I would have preferred more flexibility although you can program the memory data such that those channels you want to skip are outside the selected range If you want to search through a certain frequency range you use the sweep feature Again you select the start and stop frequencies and then hit the RUN button There are user options to set the time the radio will spend on each channel or frequency 0 5 to 5 seconds for scan and 0 05 to 0 5 second for sweep The default condition is to continue scanning after that time whether there is a signal on frequency or not Again you can change that condition with a user option so the radio will pause on that channel or frequency as long as a signal is present Memory channels can be used in so many ways The ability to store a frequency so you can come back and check it later is invaluable The 535D has 200 memory channels the same as the 525 all tunable and each one stores all operating information such as mode bandwidth and AGC setting I found that changing between VFO and memory operation was a bit quirky as it was with the earlier NRD 525 When you first switch from VFO to memory operation the radio displays the frequency that was on the dial with all the same operating settings but showing the last
39. ven provides wiring diagrams for those rear panel connectors that aren t immediately obvious There is a brief section on adjustments and maintenance and another on troubleshooting While neither of these will take the place of a service manual they should help you solve the basic problems Detailed descriptions cover the installation of optional units The last 12 pages of the manual include a one page block diagram of the radio and detailed schematics The details are in rather fine print however Options For the CW buff JRC offers optional 500 and 300 Hz CW filters for the NRD 535 There are a couple of other optional units that should catch an active ham s eye The RTTY demodulator will copy the CCITT No 2 alphabet Baudot RTTY with any of the common frequency shift widths and speeds You ll have to connect your computer to the RS 232C interface to read the text though There is also a high stability reference oscillator unit which includes a constant temperature crystal oscillator to provide a reference frequency for the synthesizer This unit provides a frequency stability within 0 5 ppm over a temperature range of 20 C to 50 C I didn t find frequency drift to be a problem without this option Inside the set you ll find that JRC has retained the computer style construction method it used in the NRD 525 If you re curious enough to pop the cover you ll find that a mother board covers
40. you interpret the numbers and charts The report even includes a summary of how this radio stacks up with similar previously tested units Reports are 7 50 for ARRL mem bers and 12 50 for nonmembers postpaid Request the C 756 Test Re sult Report from the ARRL Technical Department 225 Main St Newington CT 06111 personal checks accepted For credit card orders only call 860 594 0278 Japan Radio Co NRD 535D HF Receiver Reviewed by Larry Wolfgang WRIB Senior Assistant Technical Editor I don t own a transceiver with general coverage receive coverage and I haven t done much shortwave broadcast listening lately so getting my hands on this receiver was a treat The NRD 535D first introduced a half dozen years ago has proved an able and popular performer among SWL BC DXers but many hams might not be familiar with it I found it to be a full featured radio that is at home on the ham bands as well as outside them so if you ve got a yen for listening you might want to check out this fine receiver The NRD 535D is the fourth generation in Japan Radio Company s line of general coverage receivers We didn t review the NRD 505 but we reviewed its similar looking predecessor the NRD 525 almost nine years ago see QST Jul 88 and its predecessor the NRD 515 seven years before that see QST Nov 81 The NRD 535D retains many of the features of the predecessor 525 and some of its flaws Those famili
Download Pdf Manuals
Related Search