The Icom Ic Hf Transceiver

A sturdy and popular rig.

I 'm lucky enough to be frequently ottered new equipment for review. and my luck was running well in early April when 73 arranged to have a new IC-738 delivered to me for this purpose.

The IC-738 has been on the market long enough that it's already popular, as is its more pricey sibling, the IC-736, There are only two differences between these units: The IC-736 offers 6 meter (as welt as HF band) coverage and has a built-in AC power supply- while the IC-738 lacks 6 meter coverage and requires an external source of 13.8 VDC power The two ngs share a common owner's manual and most other features Because the IC-738 lacks an internal power supply, it weighs less (19 lbs) than the IC-736 (23.1 lbs) and may be easier to handle for field operations, As far as t can tell, the IC-736 has no provision for externa* DC power at all. making H a base station rig in every sense.

Despite the 738's lighter weight and potential batlery-power operation, it too, is really a base station radio because it is not small. Measuring 13" x 4.4* x 11.2" (H x W x D), the IC-738 has the look and feel of a real radio. Most of its controls are targe and spaced far enough apart for even clumsy fingers and its display s large enough to be viewed from across a large room. The icom s 59 panel-mounted controls are easy to use with the possible exceptions of the RF-gain and power output controls,

The IC-738 comes well-packed and includes most items needed to get on the air quickly, save for power supply and antenna. Its instruction manual is reasonably complete and well wntten. The transmitter output power is rated at 100 watts SSB, CW, and FM, without any note regarding possible derating requirements for high-duty-cycle operation {like FM or RTTY), I don t know whether Icom would consider it safe to operate at 100-W output continuously or not Also the specifications discuss only SSB. CW FM. and AM. and doiVf mention the digital modes except

Photo A. The iC-738 has a clean, uncluttered front panel that's user-fhendty with a huge main display

for bnef connection instructions on page 16 of the manual, which state, "The transceiver does not have an FSK mode for RTTY, AM-TOR, packet, etc.; however you can operate these using AFSK in the SSB or FM mode/" I'm neither a Digitai Oemon nor a Binary Bimbo, but even so. I d expect more discussion of such a popular subiect.

Strengths

A point in its favor, though, Is that the IC-738 passed my 'Can I use this radio without opening the manual?" test with flying colors. I had the rig out of the box and on the air and completed my first 50 or so contacts, without ever glancing at the manual. And that's good. This is important because, in an emergency, there may be no time to indoctrinate operators; they need to sit in front of the radio and use it immediately. The more intuitive the rig is to operate without instructions, the better its design, as far as I'm concern ed. On a scale of 1 to 10.. I'd give the IC-738 a for intuitive use. I d have given it a MO," except its built-in. two-port antenna switch {frontpanel controllable) kept switching to the unused port as 1 switched bands, making me scratch my head about why signals seemed so weak on bands where I knew they should be strong1 (The IC-738 remembers which antenna position was last used on each band, and reverts to it. As it comes from the factory, who knows how it will be set up? You can override this feature, but it is not intuitive and probably requires an instruction reference )

The first thing \ noticed about the fC-738 was how uncluttered its display fs. On power-up, the display panel indicates VFO frequency, mode tuner status. VFO selection (A or B). and channel number for memory operation. That's it! I like the tidy display, and only wish it omitted the channel number unless memory operation is actually in use. It would then display only what the operator absolutely has to know. The frequency indicator numerals are large {12" high) and very easy to read being dark gray segments against a bnght orange background. The display is readable even operating outdoors on a sunny day.

The second thing I noticed is how quiet the receiver is. Unless the PRE AMP is activated, the noise level on every band tends to indicate about SO (no reading) and the ambient hiss between signals is very slight. This tempts one to turn the volume up very high, to hear something+ Then, when you tune across a signal, the sound jumps out at you from the rig's top-mounted speaker. The background noise is so low that you wonder if the receiver has the sensitivity we ve come to expect from modem equipment. It does. The iC-738 tests as sensitive as any receiver I've come across The small amount of hiss is due to advancements in synthesizer, IF, and audio stage design. The rig is deceiving. It doesn't sound sensitive until you need it to be and then M s right in there with the best of them,

Weaknesses

Within a few QSOs made, I was able to find a few shortcomings with the Icom—not in performance, but in creature comforts. For example, the analog metei indicates only one of three possible data on transmit: either power output (watts scale), SWR (1 to infinity, with SWR = 3 at center scale), or ALC activity (thick normal' range} However, there is no way to tell which scaie is active. There is no three-position panef-mounted swrtch to which to refer. The meter is switched by a single push-button, which toggles the meter mode between the three possibilities.

Another example is the power level control, which, like the receiver RF-gain control, is a small knobless shaft protruding through the front panel to the lower left of the main VFO tuning knob. While I dont find myself adjusting RF gain much, I do frequently like to change transmitter output power. This is a control thai gets a real workout in my station, as I ve never been an "AKTFT (All Knobs To flight) operator if I work somebody very strong, i tend almost automatically to reduce my power, if the station worked is very weak, f almost automatically turn it back up. Rapid-fire contesting notwithstanding, I adjust this control a lot, and know many others who do, too. The !C-738fs control lor this function is too smail to be easily and repeatedly adjusted.

One other thing that struck me as inconvenient is the placement of the VOX controls which are on the rear panel, it is inconvenient to have to reach around behind the rig to make adjustments. In many shacks, it might take quite a bit of effort, and maybe a flashlight, to do so! VOX controls, especially the DELAY control need to be more accessible.

My last gripe ts that the IC-738 Jacks transmitter mike gain. The factory-supplied handheld mike is quite good and sounds fine on the air. but has rather tow output level and requires the 738 s gain control to be run literally all the way up to make the ALC work properly

The only other complaints I might have is that the CW sidetone level adjustment is internal and requires removing the covers The ng has any CW offset you might want by using the Six control (similar to a receive RIT, put works the transmitter offset), but the sidetone pitch always remains the same As a true CW operator, I like being able to adjust everything f can when using this mode.

Okay enough gripes. Other than these small issues, the IC-738 works really greatl

Strengths again!

if you re already familiar with modem FF gear, you won t need any training in how to use the Icom, if this is your first modem HF transceiver, read the manual and try out each function one at a time, I like that the 738 has two key input jacks, one of them three-circuit tor connection of a paddle to use the rig's (standard) internal electronic keyer. and a separate two-circuit jack for use with a straight key, Dug." external keyer or computer control t also like ihe ng s use of a common RCA 'phono' jack for connecting the key line to an external linear amplifier. {Note: This jack is labeled SEND, which is a bit mislead-

Photo B. Rear View of the IC-738. The two side-by-side SO-239 coaxial receptacles are for two antenna connections. The cooling fan to the left side of the photo is one of fwo cooling fans used to keep the unit loafing along even at continuous duty at full power.

ingr It is connected in common with pins on ACCHI ^ ACC|2]t the two accessory DIN-jacksT and is a dual-function I/O port. If grounded, as with a footswitch, the rig wiN transmit, If connected to the key jack of most amplifiers, it will ground on transmit and cause the amplifier to keyr) I happen to like RCA phono plugs and jacks mostly because they ve been around tor generations, are likely to be in nearly everyone's junk box, and can be picked up inexpensively at a Jocal Radio Shack in a pinch. DINs are fine, bui are also the kind of rhing you mighl forget to brung to a DXpedttion; DINs are also difficult to assemble in the field.

Operating

My first 30 or 40 QSOs with the new JC-738 were on CW. my favorite mode, (1 can hear the boos and hisses but to each his own.) The rig had no trouble producing more than 1GQ-W output on every band. The semi-QSK worked great and so did the full QSK (break-in) mode, up to at least 45 wpm.

On SSB. the stock microphone lacks punch unless Ihe mike gain is turned fulfy clockwise. 111 guess that Jcom might have a fix for that by now. I did try using one of my favorite desk mikes, an old American-made Shure 444 (big and clunky, but they usually sound good}, and it produced far more punch than the stock hand-held mike and reports received were excellent. With the 444, I was able to turn the mike gain down about halfway and still have sufficient audio to get an ALC indication. The IC-738 has a built-in speech processor whose function is labeled COMP (compression) on the front panel its adjustment is also labeled COMP and is located on the rear apron of the radio, next to the VOX controls. The compressor worked pretty well, allhough stations contacted advised my audio sounded more natural with it off This is a pretty subjective issue, and I'm used to getting mixed reports about speech processors and compressors. Despite most stations' reports telling me 1 sounded better with it off. the compressor did its job of increasing PEP output power as indicated on my Autek WM-1 PEP computing wattmeter.

This is afl one can ask for from a simple speech compressor circuit

The rig's JF bandwidth, stated as 2 1 kHz (-6 dB), is very adequate for SSB work, but mighi be too wide for crowded CW operation. J liked the way the receiver sounded with the factory-equipped filter on SSB. it was tight enough to prevent much adjacent-channel interference, but wide enough to allow excellent fidelity of received signals, t thought it was just about the proper balance, and the receiver is one of the best Ive ever listened to. Although t have four modern HF rigs, my standards of comparison for HF receiver performance are older equipment that in many ways outperform the latest gear. I use a 1978-vintage Drake TR-7 (transceiver) and a 1958-vintage Collins 75A4 (receiver). Beheve it or not, these old-timers offer better performance under some conditions than anything built since, If a modern synthesized transceiver can hold its own against these two radios, I'm usually astounded, The IC-738 comes very close.

The IC-738 is one of the few modem HF rigs I ve used having a receiver that I like listening to on SSB I did not have at my disposal the optional narrow CW filters on the review model, so I can t comment on ihem. But the standard SSB filter works very wel]t and the optional filters are plug-in, not solder-in (although installation does require removing the radio's covers}.

The 73B s standard, built-in ATU (automatic antenna tuning unit} is fast and smooth as silk, J was extremely impressed with it. The ATU is activated and then implemented with a single push-button control rTUNERj A fast push activates it,, and a longer push engages the tuner, which makes the Iransmitter operate at reduced power until the tuner finds a nearly perfect match point I could not find any point in any band where I couid not achieve a nearly perfect match with the antennas I normally use, f could even gel my 6 meter vertical so load up on 80 meters, as well as achieving success with my 160 meter dipole on every single band, including 10 meters.

As an experiment, I tried loading up a 12" long Radio Shack clip lead (#20-gauge wire with an alligator clip on each end) on 20 meters II clipped the far end of the lead lo a paper poster hanging on the wall (a contest award, actually'] and the rig found a match within a few seconds. I answered a strong W5 in Arkansas, and completed a contact with the clip-lead antenna. I should note that my shack is at ground level, enclosed within the house and having no windows to the outside. This is not a very objective test, and I have no way to measure the impedance of the dip lead on 14 MHz but it goes a long way »n demonstrating the effectiveness of this tuner

The ATU obviously has memories, and seems to know how to retune itself (once set points have been established by prior use) as the receiver is being tuned across each band. The problem is that I don l know how many tuner memories it actually has. because the manual does not address this point. The ATU also retunes itself to the presets as one tunes around on the receiver which makes transmitting at full power on nearly any frequency as easy as pressing the PTT button or key: but the manual does not discuss this point either. This is a shortcoming of the manual: The rig has features that work very well but aren't even mentioned!

The receiver s PREAMP works well to boost receiver sensitivity en lhe higher bands like 10 meters, but serves no usefuf purpose on the noise-laden lower bands. (This is typical of many modern HF rigs. Nobody needs a preamplifier when using any reasonable transmitting antenna to receive below 10 MHz.) The IC-738 also has an ATTenuator, which reduces signals reaching the front end and might be useful when receiving on or near the frequency of extremely strong signals.

The IC-738 contains the normal comple^ ment of features and functions found in HF base station transceivers of the nineties. I've already mentioned most of the important ones, but a tour of the rig s panel controls would be incomplete without mentioning these as welt.

The AGC switch is a push-button that toggles between FAST and SLOW, Although it lacks an OFF or MEDIUM mode I found it satisfactory for most operations The AGC performance is good Concentric to the voi-ume control (labeled AF) is a squelch control (SQL) that functions on all modes but is normally used only for FM work in the 29.6 MHz range. The rig has a pulse-type noise blanker activated by a push of the NB switch It works as well as most I ve used and does a fine job of reducing ignition noise.

The buili-in electronic keyer for CW work has a speed control (KEY SPEED) concentric to the mike gain (MIC) control and adjusts smoothly from 7 wpm to 41 wpm. The keyer works fine, but I usually use an external memory keyer for contest work Still, an internal keyer is handy in a pinch or for portable work. The previously mentioned antenna switch is an internal relay that is activated by a press on the ANT button above which are mounted two LED indicators to indicate the antenna (T" or "2 r) selected, The ANTenna selection data is normally automatically stored in band memory, but may be overridden at any time by a push of the ANT button.

The RF PWR control adjusts the rig's output power from less than 5 W to full output MOO W except on AMt where the max is about 40 W) It works well and adjusts output smoothly, but 1 wish it had a larger knob to make for easier frequent use. Just below the

Icom 736 Vco Box Location
Photo C. Inside the IC-738. bottom view. The rig has a clean layout and appears easy to service. To the right, in the shielded compartment, is the ATU {automatic antenna tuning unit)

main VFO tuning knob is a tuning brake adjustment screw, turned by a small Phillipstype screwdriver, to vary tuning dial tension. I found the factory setting just about perfect, but you can adjust this to your heart's content, from quite loose (allowing a spin across the band) to fairly tight (won't jar the knob even if the rig is bumped hard).

The main VFO tuning knob operates smoothly and has a weighted feel Large enough to provide a comfortable grip, it also has a large circular finger-hole depression for raptd motion using a single finger. I liked it a lot. This is one of those features that many hams overlook, but can make a real difference in operating, especially for long periods (like contesting). \ wish every rig out there had a tuning knob like this one Just above the tuning knob is an electronic dial lock switch (LOCK) which prohibits the VFO from changing frequency. I never actuaMy use this function, although most modem rigs offer it.

The IC-738 offers 101 channel memories and six pages of the owner's manual are devoted to describing its operations. The memories wilt store frequency, offset, mode, antenna selection and so forth. The memories can be of great assistance in a variety of ways, but I use them moslfy for rapid band and mode changes, or to store repeater frequencies in the 10 meter FM subband. A very handy feature is the IC-738 S scratchpad memories. These are five additional memories (extendible to 10 if desired) which do not occupy space in the normal 101 memory register and can be instantly stored and recalled with a single push of the MP-W (Memo Pad-Write! or MP-R {Memo Pad-Read) button, tf you want to store the frequency to which you're tuned, and then tune somewhere else, just punch the MP-W button and spin the knob. A single push of the MP-R button instantly recalls where you were before you tuned around. These memories stack up. and the factory default allows stacking five of them: if you add a sixth, the oldest one stored will drop out of the memory, and you H be ible to recall the latest five This Mature is very handy when DXing or contesting, and easier to use than the other 101 memories.

which require more thinking and keystrokes.

Like any good modern rig, the IC-738 has a frequency/band keypad. a set of 12 push-button switches that can be used to change bands instantjy, or access specific operating frequencies without the need for spinning the VFO knob. Eleven of these buttons are labeled with band designators and/or the numbers u1" through "0. plus a decimal point, if you re on 80 meters and want to switch to 10 meters instantly, just push the "28 button, and you're there, right on the last 10 meter frequency used, if you want to dial up a specific frequency without turning the VFO knob, that's easy, loo For 14.225 MHz, you'd press FREQ (NP {frequency input), followed by 1-4—2-2-5, followed by ENT (entef).

Another way to tune around besides using the VFO knob is to use the UP and DOWN buttons, located below the keypad just discussed. If you press and hold either button, the rig will electronically tune up or down the band in programmed steps from 1 kHz to 1 MHz. Having ihis function on the front panel is almost superfluous however. The Junction may be duplicated with the UP and DOWN burtons atop the handheld microphone {and also found on most desk mikes). That can be handy,

Operating "split1, with the 738 is as easy as with most modern rigs, and involves using the SPLIT button in combination with the A, B (VFO ^A" or JhB' select) button, llf you wish to check your transmit frequency instantly when operating split, a push of the XFC (Transmit Frequency Check) button will toggie the VFO from the receive VFO to the transmit VFO, If you press XFC and hold it down, the VFO knob may be tuned To change your transmitter frequency to anything desired, without changing your receiver frequency. When you release the button, your transmitter frequency will be vtiaiever was lasi tuned. Very handy for working split-frequency pileups

A Quick Tuning switch \TSt for Tuning Speed) allows changing the VFO tuning speed from normal (1 Hz or 10 Hz, user-selectable) to fast (1 kHz) for rapid band excursions. When IIle normal (slow) tuning mode is selected to allow i Hz tuning, a third numeric indicator to the right of the frequency decimaJ point iliumtnates; otherwise when the normal tuning mode ;s 10 Hz. this digit is blanked and not pari of Ihe frequency display. Not a bad idea. Using the 1 Hz tuning mode can be painfully slow and is rarely necessary (can you really hear a 1 Hz change?), although it might be nice when using a sharp CW filter and the NOTCH function,

The mode selector buttons are easy to use and large enough to operate quickly. Located just to the left of the main VFO tuning knob, the mode switches are labeled SSB (toggles between LSB/USB); CW/N (toggles between CW wide and CW narrow if the optional nar row filter is installed); AM: and FMrTONE (toggles between FM and FM+CTCSS tone [encode] if the optional UT-30 tone encoder is installed).

The 1C-73S, like most recent tcorn products tor HF, has both RIT and XIT functions. RITt Receive Incremental Tuning, is featured under various names on ail HF transceivers made in the past two decades or so. XIT allows similar adjustment of the transmitting frequency, independent of the receiving frequency. Using either one or the two together, you can work split up to about 20*kHz separation, without needing to use the SPLIT function. The RIT and XIT functions are indi-viduaily addressable but share a common tuning knob labeled RIT/aTX.

The rig also has two interference-fighting tools: PBT (PassBand Tuning) and NOTCH filtering. The PBT control has a center off detent, while the NOTCH control has its own separate on/off switch. I found the passband tuning PBT function extremely helpful under a variety of situations, but the NOTCH not particularly useful. Notch filters are mostfy intended for reducing the intensity of an interfering single-frequency carrier, and donTt help much in reducing interference from a nearby SSB station. Used in combination with some patience and skill, the PBT and NOTCH can complement each other to further reduce some types of interference. But I think the PBT will be of greatest help for most users, and the one in the IC-738 is good.

The unit has the usual scanning features that may be used to frequency-scan between memories or preset band limits The scan modes are "programmed scan," "memory scan," and "select memory scan," and are described in two pages of clear instructions within the manual.

Technically speaking

The IC-738 uses a triple-conversion receiver with "up conversion* as has become the norm. Its receive first tF is at 69 MHz, second IF at 9 MHz, and third at 455 kHz. allowing the use of conventional bandpass filters. Foi-iowing The signal path from the antenna jack, received signals are first routed through the antenna switching relay, then through the T/R relay, a iow-pass fitter, and the receive attenuator switch before they reach either a low-pass filter for reception up to 1.6 MHz. or a set of diode-switched bandpass filters for coverage of 1.6 through 30 MHz. Seven such bandpass filters are employed, each covering an octave or less.

The filtered signais are routed to the re* ceive preamplifier switch, where, if the preamp is engaged, they are amplified by a pair of 2SK2218 JFETs in parallel. Signals are low-pass filtered once again before reaching the first RF mixer, a pair of balanced 2SK2171 JFETs, then are bandpass filtered at the first IF of 69,0115 MH* before being amplified by the first IF amplifier, a 3SK121 dual-gate MOSFET. Received signals are then bandpass filtered once more at 69,0115 MHz before being mixed down to the 9.0115MHz second IF in a diode balanced mixer, type ND4B7CIT LO njection to Doth mixers is provided by the PLL unit. The first mixer infection provided by the PLL tunes from 69.0415 through 99.11499 MHz, thus allowing continuous receive coverage of nearly the entire 30-MHz spectrum. This output range is achieved by four VCOs having outputs 69.0115 MHz above the received tuning range. (For example, VCOl produces 69.0145 Through 76,0114 MHz; VC02 produces 76.0115 through 84.0114 MHz, and so forth). The second mixer injection at 60.000 MHz is provided by a frequency-doubled 30MHz crystal oscillator, also located in the PLL unit.

The 9.0115-MH2 second IF is filtered using another 2-pole bandpass monolithic device, after which the noise blanker gate is located. The noise blanker gate is a set of four MA77 diodes driven by a gate control circuit located on the output of the noise blanker loop. The noise input to the blanker is sampled at the 9-0115-MHz IF and is amplified and detected in a noise blanker AGC loop of its own prior to dnving the gate control circuit. After the diode gate, the 9-MHz IF signals are amplified once more and then bandpass filtered by one of two 9-MHz crystal filter units. (The 2.1kHz unit is standard, but an optional narrow CW filter may be installed at this point as well. AM or FM signals continue through the

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