Kenwood TR-751A Multi-mode VHF Transceiver
A standard for years to come.
An old saw claims that the more things _ _ change, the more they stay the same. It's only partly true for amateur radio. Radios still transmit and receive, and still use RF. but features of our radios have changed radically over the years.
Hams in the hobby more than five years will have seen HF rigs become synthesized, miniaturized, and microcomputer-controlled HF rigs now have dual VFOs, built-in general coverage receivers, built-in narrow CW and SSB filtering, up to 100 memories, and the ability to be controlled by an external personal computer. There's even a rig—the Yaesu 767—that serves as the platform for not only a complete HF station, but also a fairly complete VHF/UHF station An operator can add modules on it for 6 meters, 2 meters and 70 cm.
If this is the case for HF, imagine what's been happening at VHF and UHF.
Rigs have become incredibly compact and are still capable of 25 to 50 watts of output. VHF rigs have 10 to 20 memories and can have such items as built-in CTCSS tones for tone access, digitized voice, limited access, and liquid crystal displays.
Contrast this with one of the standards of a few years ago. the (COM IC-255A. It was state of the art for 1980 and sported a microprocessor, light emitting diode display, dual VFOs. RIT, five memories, and high or low power. (All this is standard now ) 11 also had more than enough audio and was about as rugged
a transceiver as we've run across in a long while.
However, the radio was big. on the order of about five pounds and measured in at about 6" x 8" x 2". Also, it didn't sport many of the features we take for granted today, such as repeater reverse, repeater offsets stored with frequency, priority channel, built-in CTCSS tones, and the ability to resume scanning after it had found a busy frequency.
The state of the art only seven years ago was far different than it is now.
Let's return to today's state-of-the-art and look at one of the more capable multimode VHF rigs on the market, the Kenwood TR* 751 A. It is an example of just how far the radio art has come in less than a decade.
For starters, the TR-751 A has a GaAsFET front end. something that was only dreamed about a few years ago. This development radically increases the sensitivity and dynamic range of the TR-751A. In fact, when I checked my TR-751A against one of the standbys of the 2-meter multimode world, the ICOM IC-251. we found that the 251 needed a preamp to match the performance of the TR-751A right out of the box.
Further, the TR-751A is far more linear in its operation While tuning through a signaf with the IC-251, the operator can hear the distinct frequency changes in the signal's beat note. It
sounds not unlike a multi-tone commercial paging device. In contrast, the TR-751A tunes smoothly through the signal with no trace of a changing beat note.
Introduced last year the TR-751 A's built-in microcomputer programming has an interesting feature When in the Channel Search (CS) mode, the TR-751 A wails for a similarly equipped Kenwood with the same feature activated. Once it senses that it has connected with another Channel Search-equipped transceiver the TR-751 A synchronizes with the other unit and they both hunt for an open simplex frequency—presuming they are in simplex range, of course—and both rigs automatically QSY.
It's a great way to keep repeater use to a minimum, especially when the operators are capable of simplex operation. How many times have high-power VHF transceivers been used for repeater operation from fixed stations? M seems that more and more, repeaters are replacing simplex or 75 meters for local ragchewing, which isn't the purpose of repeaters in the first place. Repeaters are meant to allow reliable mobile communication when two mobile stations are out of sight of one another or for low-power station-to-station work when the radio's output can't be used for simplex work. Hams outside North America tend to appreciate this point much more.
The TR-751A uses a liquid crystal display (LCD), Much like a personal computer's CRT, the backlighted, green LCD displays frequency down to the nearest 50 Hz, It also indicates whether the operator has the alert feature activated; the frequency increments (50 Hz, 5 kHz, etc.); memory recall mode; the shift (plus, minus or simplex) for FM and repeater work: optionatsubaudible tone selection; and the frequency lockout. Further, the LCD indicates when it is in "open channel" search mode, and when the coded squelch option has been activated. The "open channel" search is one of the newest features of the Kenwood VHF lineup.
The LCD also has a standby mode indicator, which shows the features in that mode, an indication the TR-751A is in memory moder where the memory number is indicated, and whether the RIT is activated.
The TR-751 A's front panel is clean, easy to use and, sensibly arranged. All of the functions dealing with frequency are grouped in the upper left, while functions applying solely to radio operation are grouped below. In the center is a large frequency selection dial, while mode and memory buttons are grouped to the right.
The rig features a genuine analog S/RF meter that doubles as a relative power output meter. It's a refreshing change in these days of LED metering, Just above and below the S/RF meter are the status indicators, and pushbuttons dealing with coded squelch (Digital Code Squelch) and Digital Channel Link (DCL) are in the upper right. Altogether, it's a well done and well thought out front panel.
Automatic Mode Selection
This unique feature is one of the nicest on the TR-751 A. Kenwood took the ARRL band-plan and put it into silicon memory. The result is that the rig does some thinking for the operator. The allotted mode is called up automatically at a spin of th^ dial. For example, in the automatic mode when tuned below 144 100 the CW indicator lights up; above 144.100. the USB indicator is lighted. In the repeater segment of the band, the FM indicator automatically lights. It makes this multi-mode rig a pleasure to use not only in contests (mine has seen more than one) as well as mobile. Let the radio worry about which mode and concentrate on logging or driving.
The TR-751 A also has more than enough punch for most situations. With a high-power setting of about 25 watts (it measured about 28 on my wattmeter) and a low-power setting of 5 watts I found that il had more than enough power for mobile and contest work. I used a four-element beam and a short length of feedtine so the effected radiated power of the lash-up was more than competitive with other stations. The high power setting will also drive most makes of high-power amps to 200 watts.
Another nice feature is the large, finned heatsink. The TR-751A provides more than enough heatsinking to operate at high power for hours with no problems.
The Receiver Incremental Tuning is also a very nice feature. It only works on receive, but when used in conjunction with 50 Hz resolution of the LCD, the operator can zero easily in on any station. On the down side, only a small indicator in the display indicates the RIT is activated. The receiver frequency remains the same and the transmit/receive frequency offset is not obvious.
On the air, the GaAsFET front end easily picks up weak stations and, even though the rig is very sensitive, it didn't complain in the presence of other RF signals. There was some increase in received noise, but it wasn't bothersome. A small adjustment of the RF gain control took care of overly-loud stations.
The noise blanker is also effective against most kinds of pulse-induced noise, such as ignition noise. It managed to quiet more than one noisy ignition when I was using it mobile. The transmit and receive audio are superb in both FM and SSB modes.
The only things I fault are the documentation and the price. At over $600 for the basic rig without the Tone Encoder or Voice options, it is quite expensive, especially for a single
band multimode rig. The ng offers FM. sideband and CW. as well as DCL and a GaAsFET front end, but it's just as true that it's only for one band, rather than two, I suppose it's as much a result of the yen-dollar readjustment, which has made just about every imported item expensive.
The documentation seems as if it were written by a person with little knowledge of the American idiom. It's rough and makes little sense in places. However, it does come through in the areas where it has to: programming and using the rig. The graphics are first quality and carry the user guide where the language falls down.
Overall, I enjoy using my TR-751 A, II has some great specifications and quality features. And. like its predecessor. theTR-9130t the TR-751 A should be a standard for many years to come.
Marc N1BLH is an engineer at Digital Electronics in Boston. He reviews regularly for 73.