IC-703_review_RC_2003.pdf

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1、The Icom IC-703 HF +50MHz Transceiver REVIEW Reviewed by Peter Hart, G3SJX, The Willows, Paice Lane, Medstead, Alton, Hants GU34 5PR; and Tom Robinson, G0SBW, 2 Beacon Heights, Point Clear, St Osyth, Essex CO16 8JW. T he IC-703 has been introduced by Icom to satisfy the growing interest in low power

2、 operation. It provides a fully featured HF + 50MHz transceiver with 5 or 10 output, tailored to the requirements of the Foundation Licence, and meeting the needs of the QRP enthu- siast and the amateur who likes to operate portable. The outward appearance of the IC-703 is virtually identical to the

3、 well-established IC- 706 series and operation and many of the features are very similar. However, under the bonnet the architecture, circuitry and layout are substantially different. BASIC FUNCTIONS The IC-703 is a compact radio meas- uring 167W x 70H x 235Dmm and weighing about 2kg (the manual has

4、 the dimensions incorrect). The front panel is detachable and may be oper- ated remotely with an available sepa- ration cable. The microphone, which uses RJ telephone style connectors, may be plugged into either the front panel or the rear panel and an HM- 103 electret hand microphone is pro- vided

5、as standard. The radio is designed to operate with power supplies in the range 9 to 15.8V. Above 11V the transmitter provides 10W maximum power output. Below 11V, the trans- mit power is limited to 5W and power saving measures are automatically selected, principally by switching out the LCD backligh

6、t and button illuminations but also reduc- ing the receiver current giving a lower dynamic range. Low current consumption has been a major consideration in the overall design of the radio and a power save mode which sequences to lower current with no signal is selectable. All power saving functions

7、are user selectable. The transmit power output can be set to one of fi ve maximum levels: 10, 5, 2.5, 1 or 0.5W and within these maximum levels the power output is fully adjustable down to less than 0.1W. The receiver tunes continuously from 30kHz to 60MHz and the trans- mitter is enabled for segmen

8、ts around each of the amateur bands. LSB, USB, CW (normal and reverse), AM, FM and various data modes are provided. Data allows for both FSK and AFSK operation. FSK provides RTTY operation where the radio gen- erates the tones from a digital input. AFSK is provided by SSB-data mode and is used for a

9、ll audio tone inter- faced modes. Two main printed circuit boards contain the bulk of the circuitry. The lower board contains the power amplifier and output filters, auto ATU and controlling processor. The upper board contains all the remaining signal circuitry includ- ing DSP. The detachable front

10、panel contains the control interface and display processors. Overall a rugged construction has been achieved without the need for a fan on transmit. A 6cm diameter speaker fits into the case top. A carrying handle is not provided but is available as an extra if needed, as is a mobile mounting bracke

11、t. The receiver is a double superhet on all modes with IFs of 64.455MHz and 455kHz with the main selectiv- ity being achieved using ceramic filters at 455kHz. One optional extra filter may be fitted from the available filters for narrow CW (250 or 500Hz), narrow SSB (1.8kHz) or wide SSB (3.3kHz). Th

12、ese are quite expensive but give excellent per- formance. A 500Hz CW filter was provided with the radio and was also useful on data modes. Note that the IC-706 is also double con- version on SSB/CW but with IFs of 69MHz and 9MHz and achieving main selectivity at 9MHz. Optional filters in this freque

13、ncy range are cheaper. Two multipin connectors on the rear panel allow interfacing to data terminals, linears and external auto antenna tuners. A 13-pin DIN plug with lead tails is provided, the other is a standard 6-pin mini-DIN. There is a separate connector for the Icom AH-4 tuner and set-up opti

14、ons allow appropriate control of exter- nal auto-tuners. The built-in tuner covers all bands from 1.8 to 50MHz for VSWRs up to 3:1 and adopts relay switched inductors and capacitors with memories for fast October 2003 RadCom www.rsgb.org After Peter Hart had carried out his usual thorough lab measur

15、ements and tested the IC-703 in the shack, we sent Tom Robinson out and about with the transceiver and its portable accessories to try it in the fi eld. 25 tuning. The relays are latching types to min- imise continuous power drain. The rear panel key jack accepts a key- ing paddle used in con- junct

16、ion with the inter- nal keyer, a straight key or an external keyer ac- cording to set-up options. The front panel headphone jack is switchable to provide external speaker output in addition to the external speaker jack on the rear panel. External computer control is included via the standard Icom CI

17、- V serial interface which requires a level converter to RS-232C. The radio is provided with a comprehensive 106-page manual but no technical description or cir- cuit details are included other than the specifications. A basic operation section is included as a quick reference guide to assist beginn

18、ers. Keep the manual to hand, as some of the more exotic functions are quite complex to use. FEATURES In addition to the usual dedicated controls and keys, four multi-func- tion buttons below the display select most of the remaining functions of the radio. These functions are grouped into a number o

19、f scrollable menus. Two of these menus allow for user set-up and three access the wide range of radio features. The initial set-up mode, which accesses 43 of the set-up parameters, can only be accessed by turning off the radio, turning it on, setting the parameter, turning off and on again, which is

20、 a little long-winded. The detented 40mm diameter main tuning knob has a friction adjustment lever but a somewhat dead feel. Tuning on SSB/CW/RTTY modes is in 10Hz steps / 3kHz per knob revolution or 1Hz steps / 300Hz per revolution with a faster and programmable tuning rate selectable. On CW and da

21、ta modes it is possible to tune even slower at one quarter of the normal tuning rate. On AM and FM 26October 2003 RadCom www.rsgb.org For the Field Trials, in addition to the IC- 703 itself, Icom (UK) supplied the LC-156 multi-bag, BP-228 battery pack (and its 600mA charger) and OPC-581 separation c

22、able. Because Icoms promotional litera- ture states the IC-703 is partly aimed at Foundation licensees, all the fi eld trials were conducted using SSB. In keeping with the IC-703s lightweight, go any- where ethos, all the equipment was eas- ily carried to the sites by one person. ACCESSORIES USED Th

23、e BP-228 9.6V 2800mAh NiCd battery pack weighs 1lb 9.5oz (715g) and took six hours to charge using the supplied charger. It performed well in the fi eld, giving well over two hours of 75:25 receiving/transmitting and still allowed a further three hours of listening in the shack, at the end of which

24、it still had spare capacity. During this period output was limited to 5W by the IC-703s effec- tive power saving circuits.The supplied 100-240V battery charger has four inter- changeable mains plugs; very useful for the world traveller. It has automatic charger circuits for both NiCd and NiMH packs

25、and a button operated battery dis- charge function. The LC-156 Multi-Bag is well made and well thought out. It has many fea- tures including a secure harness com- plete with chest strap and convenient hooks on the shoulder straps, front pouch, side pockets, controller case, six Velcro antenna fasten

26、ers, loops for hold- ing the separation and power cables, padded area for the battery pack, and two, sealable, holes in the sides for run- ning out leads to the antenna and the controller. It also has a built-in rain cover which folds neatly away when not in use. A minor criticism is that the Velcro

27、 antenna fastening straps are short.A 7/8in (22mm) diameter tube was gripped very securely but one of 1in diameter was not. FIELD TEST RESULTS The fi eld tests comprised two picnic table portable and two pedestrian mobile (manpack) confi gurations. The first test was also the most complex configurat

28、ion: a W3EDP 84ft (25.6m) wire antenna plus counter- poises, 4:1 balun, curly tail earth spike, 33ft (10m) and 18ft (5.5m) fibre- glass support masts (conveniently sited trees are not available at the trial site), and a 7000mAh gelcell battery. The IC- 703s internal ATU was able to tune this end-fed

29、 wire/counterpoise system on all bands from 80m to 10m via the balun. I measured the SWR band-by- band using an Autek RF1 analyser. The worst case SWR was 8:1 on 40m but the auto tuner effortlessly brought down the SWR to 1.3:1 or less, as measured with the IC-703s meter. This was a much better perf

30、ormance than I expected, given the specifications 3.0:1 SWR maximum. Encouraged by this, I listened on the bands: 17m was almost dead and 20m not too lively. I heard a pile-up working JW6VJA (Svalbard) and gave him a call. He congratulated me on breaking the pile-up with 10 watts.A new DXCC coun- tr

31、y for me with my fi rst IC-703 portable QSO! Contacts followed on 40 and 80m with favourable comments on the audio and signal strength. I tried 17m and worked VE9KEN in New Brunswick. The DSP auto notch fi lter effectively eliminated tuner uppers and the DSP noise reduction helped improve reception

32、on 80m. A more easily-erected picnic table station used the Buddipole, a commercial coil-loaded dipole covering 40 to 10m supported on an 11.5ft (3.5m) fi breglass painters pole fastened to an in situ wooden post.Again, the gelcell battery was used.The antenna was only 15ft above ground so I operate

33、d NVIS on 40m.The Buddipole does not require a tuner, but careful adjustment is needed to get a 1:1 SWR.The internal tuner on the IC-703 made light work of bringing an intentionally poorly adjusted Buddipole to less than 1.3:1. The IC-703/Buddipole combination seemed to work as well as most of the o

34、ther stations heard on 40m. 57 reports were typical from British, German, French and Russian stations and mini-pileups associated with special event stations and LX/PA1AT proved no problem. For pedestrian mobile operation, the LC-156 multi-bag, OPC-581 separation The Field Trials REVIEW Close up of

35、LC-156 bag with added antenna support frame. only a higher and programmable tuning rate is selectable together with 1MHz steps. At high tuning speeds auto speed-up is engaged fairly seamlessly. The receive fre- quency can be shifted independent- ly of the transmit frequency using the RIT control on

36、all modes except AM and FM over the range 10kHz. Alternatively this control can be assigned to parallel the main tuning knob. Bands are selected by up/down buttons returning a single frequency per band. The usual A/B twin VFOs are pro- vided with split frequency capability, a check/set TX frequency

37、and a quick split function. There are 99 regular memory channels and a further six for storing scan edge frequencies, and memories can be tagged with alphanumeric names up to nine char- acters long. There is a one press store and recall quick memory feature allowing fi ve or 10 frequencies to be acc

38、essed rapidly providing the rele- vant menu line has been actively selected. Scanning features allow scanning between two programmed frequencies, across all non-empty memory channels or across selected memory channels. One memory channel can be designated as priority watch for repeated checking. Rec

39、eiver features include selectable RF preamplifier/attenuator, fast/ slow AGC, IF noise blanker for igni- tion type noise and IF shift to move the receive passband away from interfering signals. Audio DSP pro- vides a noise reduction facility and an automatic notch fi lter that has the capability of

40、notching multiple and moving tones. Having incorporated DSP, it is surprising that more DSP features were not provided, eg audio fi lters. The DSP unit is fi tted as stan- dard in the UK but this is not neces- sarilythe case in other countries. A combined RF gain/squelch control may be programmed to

41、 function as either an RF gain control or squelch sepa- rately on SSB/CW and AM/FM modes. Transmit features include a speech compressor and VOX on SSB and full or semi break-in together with a full message keyer on CW. Keyer parameters are programmable and three message stores with up to 50 characte

42、rs per store are provided together with contest serial number auto-incrementing and auto-repeat of messages. For the FM operator, the radio is equipped with a CTCSS tone 27October 2003 RadCom www.rsgb.org cable and BP-228 battery pack acces- sories were used, largely duplicating that shown in Icoms

43、advertisement for this rig. QRP, coupled with small, ineffi cient antennas, is a recipe for disappointing pedestrian mobile performance so I decided to use my proven 13ft (4m) whip antenna.To support this adequately it was necessary to make a light frame and fasten it to the LC-156 using the bags an

44、tenna fastening straps.While walking this bag/frame combination pro- vided a stable antenna mount. During an early morning seven-mile walk, 20m was open with lots of DX, including Hawaii.The best I could achieve though was a 56 from a station in Italy.The autotuner, again, had no problems tuning the

45、 whip.This confi gu- ration proved to be the lightest (12lb) and most comfortable pedestrian mobile backpack I have worn, and would pro- vide a suitable arrangement for a dedi- cated QRPer.The breakthrough and RF feedback problem mentioned in Peter Harts review did not occur on SSB but during a shor

46、t CW test with the LC- 156/BP-228 and short whip confi gura- tion feedback was noticeable. One drawback of using the LC-156 in this way is that Icom suggests the IC- 703s power output be limited to 5W, presumably to prevent the rig from over- heating. However, I wanted to assess the rigs pedestrian

47、mobile performance at its maximum 10W using a larger anten- na. I therefore used my own ventilated backpack with its 15.25ft (4.65m) verti- cal antenna and the 7000mAh gelcell for the second pedestrian mobile trial. I was on parade at 0500UTC to catch the early morning DX.The internal auto- tuner wo

48、rked faultlessly, tuning the whip/counterpoise system on all bands from 40m to 10m.The receiver managed to pull in weak signals from VK, ZL, South America,Alaska and USA West Coast. I did not manage to break any of the pile-ups so decided to put out my own CQ. I was surprised to have my call answere

49、d by VK5HK.The ensuing QSO lasted for more than 30 minutes during which he played back a recording of one of my transmissions. Contacts with Polish, German and local M3 sta- tions followed. In the evening I repeated my walk. 17m was open and weak DX was audible (Taiwan, USA), but not workable. I received good reports from Spain, Finland and Sweden, though. Both the pedestrian mobile confi gurations used towed quarter- wave counterpoises and a 4:1 balun to complete the antenna systems. During these pedestrian mobile tests I was impressed by the IC- 703s ergonomics. I operated with the cont