Kenwood Tr

i have operated a lot of different two-meter rigs in my short life, and J am picky- When I first saw the Kenwood TR-7800 two-meter FM transceiver at a show last year, I made several unkind remarks about the rig to my companions Ha!" I said. 'Look at that ridiculous keyboard entry system. That won't work in the car!"

r now wipe the egg off my face and present my slncerest apologies to my friends, not to mention the poor tortured soul in the booth- This is one of the best two-meter rigs \ have ever used! Kenwood has designed this rig to be at home in both base and mobile applications, which is no minor undertaking.

In a way, my first impression was right—the keyboard is not easy to use while driving. What I

missed was that it Is rarely necessary to use that keyboard at all This rig is equipped with an extremely flexible memory system, which allows 15 frequencies and their transmitter offsets to be stored in memory and recalled with the push of a button on the microphone. The memories are maintained even when the power switch is off.

Add four AA nicads and the rig will ren ember your favorite frequencies when there isn't a 12-volt power supply for mites around No more peering at a washed-out display while fighting rush hour traffic. No more calling a friend feverishly while your rig is on the wrong offset. Groping for the MHz switch or the 5-KHz button also have been mercifully banished from the two-meter experience. In short, this rig offers just about every thing the dedicated FMer could ask for—either in a mobile installation or as a base station,

Basic Performance

It's no use having ali these sophisticated features if the basic performance isn t up to snuff. Before we go any further let's examine the 7800+s performance characteristics,

The 7800 is very compact, measuring only $-7^8tP wide, 2-1/2" high, and 8-1/16" deep. Electronic performance is excellent, Actually, the design of the receiver and transmitter sections of the 7800 is very simitar to thai of its older brother, the TR-7625. Many improvements have been made, but the basic design is a tried and proven one. There appears to be some additional filtering in the receiver to increase selectivity, and more reliable finals were used in the transmitter output stage.

Southern New Hampshire is not what could be considered an rf saturated area, so the fact that we never encountered any intermod problems doesn't mean too much. Still, all indications are that the 7800 should handle intermod at least as well as any other top-quality synthesized rig. Squelch action was very sensitive and sharp, more so than other popular rigs we have tested. The squelch control can be set barely above the noise threshofd, and weak signals will open the squelch1 but noise won't. Received audio Es excellent, both through an external speaker and through the JargeMhan-usual built-in speaker. Since the built-in speaker is top firing, you won't have any problems if you mount the rig on a shelf or the transmission hump of a car.

Transmitter deviation was set perfectly, as was the output of the DTMP encoder The 73 repeater uses a digital tone decoder, and if the tone levels on a pad are set too high, the decoder rejects them. The TR-7800 has one of the few pads we have seen that doesn't need some adjustment to work properly.

Transmitter output is rated at 25 Watts on high power Our sample put out over 30 Watts throughout the entire 144-147-MHz range. Low-power output is internally adjustable and we set it at 2.5 Watts. The transmitter's fina: stage is protected against high swr by sampling reflected power. As swr climbs, transmitter drive is reduced.) left the rig key-down with no toad for over a minute, and the only thing that failed was my nerve. I figure that If anyone transmits for more than a minute without any an^ tenna connected, it won't be Kenwood's fault if the finals blow"

Squelched receive current consumption was 0.4 A and maximum current required was 6 A in the high-power transmit mode. The rig draws about 3 mA even when the power switch Is off to maintain the frequency and offset memories. Four AA nicad batteries can be installed inside the case to maintain the memories when the rig fs com-pietely disconnected from a power source. The nicads will maintain the memories for several days at a lime and are automatically charged at 30 mA whenever the transceiver ts on.

In short, the TR-7800 functions so well that its basic performance characteristics can safely be taken for granted. There is nothing temperamental about this rig, so you are free to enjoy its sophisticated bells and whistles. With no further ado, let s take a good look at those bells and whistles.

Frequency Agility

The front panel is fairly simple and the controls are easy io understand. There are several methods of selecting an operating frequency on the 7800, The first is by entering the last four digits of the desired frequency on the keypad. 146.52 MHz would be entered as 6520. If operation other than simplex is desired, the offset aEso is entered via the keypad.

The second method of ire-quency selection is to scan through the band using the up/ down switches located on the microphone. The band can be scanned in 5- or 10-kHz steps, with an audio tone accompanying each step,

A third way to change frequencies IS by depressing ;he SC button on the front panel. Don't ask me what SC means—J haven't a clue! What it does is automatically scan the band looking for signals. When it finds a signal, it pauses for about five seconds and then continues its scan, if you want the 7800 to come to a complete stop, you can press the transmit switch, the C button on the tone

TR7800 (front view) with Bird Ham-Mate' Thruiine- Wattmeter 26 73 Magazine • April, 1981

Kenwood 7800

Bottom vtevr of TR-7800.

Top view of TR-7800.

Bottom vtevr of TR-7800.

Top view of TR-7800.

pad, or one of the scan buttons on the microphone.

Each time you change frequencies using oneof the above methods, the 7800 reverts to the simplex mode. Let's suppose that you are operating on 146,76r with the transmitter offset set to -500 kHz. If you scan up to 146.85. the rig will revert to simplex, and you il have to punch the negative-offset button again. This would be annoying if there weren't yet a fourth method of frequency selection. This fourth method of tuning is one of the features that makes the TR-7800 a truly outstanding two-meter rig, and it deserves close examination.

There are fifteen memories available to the 78001s operator and they hold the offset as well as the frequency. Memories 1 through 13 are programmed by entering the receive frequency and a standard offset ( + ,.-, or simplex). Memories 0 and 14 allow the receive frequency and any transmit frequency to be entered separately, so you can operate on any repeater split. Memories are selectable from the scan switches on the microphone, the SC switch on the keypad, or rotary knob on the front of the rig. The large LED readout always displays the frequency of operation, and the smaller two-digit display tells which memory has been selected.

The memories really enhance my enjoyment of two-meter activities. The ability to scan through 15 memories from the microphone makes this rig as safe in mobile use as a crystal-controlled rig, yet it offers almost unlimited frequency options, Since the rig beeps every time it steps through a frequency, you can go from repeater to repeater without even looking at the rig, much less touching it. The little keyboard also works fine, even with my large fingers, but the keyboard is a little too small to be used safely by the driver of a vehicle in motion.

The 15 memories also can be automatically scanned. When you use any rig in the bandscanning mode» it is always stopping on something that you don't want to hear. The 7800's memory scan feature ailows you to be very selective about what you listen to.

More Features

I already can hear the screams of protest from all you old codgers who were weaned on big Motorola microphones. Yes, the microphone is small, but it seems to have been carefully designed. Even my massive paws handle it with ease. There is a very good reason for Kenwood's little microphone—stick-shift cars.

Ever try to jam *er down into third with a big clunky microphone in your hand? Hard to do. You'll have no trouble shifting while holding on to the little Kenwood mike. Clearly, small microphones have arrived!

I have one complaint about the Kenwood microphone: It isn't equipped with a standard hang-up iug. It does have some kind of hook arrangement that is apparently popular in Japan, but since no mating hang-up clip is provided with the radio, you'll have to home-brew your own.

The instruction manual does a fairly good job of explaining how to connect and use the rig, and it contains a good schematic and block diagram. The manual would be a lot more effective if it made better use of the

English language. 1 would encourage Kenwood to have their manuals proofed and edited by a native speaker of English in the future! A separate service manual is also available, but it wasn't ordered In time for review.

Compulsive input checkers will be pleased with the momentary-contact "reverse" switch, which allows one to listen on the input frequency and transmit on the output frequency of a repeater,. Priority channel operation is also available. When the priority Alert switch is depressed, the 7800 scans whatever frequency is programmed in channel 0 for activity every five seconds. If there is activity, the rig beeps to let you know. You can switch over to the priority channel by pushing the priority Operate switch. Handy, eh what!

Also on the front panei is a tone switch. Activation of this switch supplies power to a usersupplied CTCSS encoder. Connections are provided inside the rig for ground, post-fitter audio input, and + 8Vdc.The +8Vdc is supplied only during transmit. The setup is tailor-made for a Communications Specialists encoder, but something could be home-brewed to fit in the space fairly easily.

To those of you concerned that all of this flexibility may be unreliable, relax. I remember a radio (which shall remain nameless) that came out a few years ago offering most of the features of the TR-7800, This disaster was filled with acres of mechanical switches and TTL Chips, Naturally, it ran extremely hot and was unreliable. The fea* tures of this rig and the TR-7800 may be simitar, but the designs are worlds apart. The 7800 uses a single microprocessor rather than discrete logic chips, and its schematic positively reeks of conservative design. It's not at all unreasonable to expect the TR-7800 to stand up to the rigors of daily use and abuse better than more conventional synthesized rigs.

There are a tot of other details that quickly endear the TR 7800 to the jaded two-meter operator. Ever scratched up a rig when you stack your two-meter rig on top of other equipment in the ham shack? Kenwood thoughtfully included four rubber feet that screw into the bottom of the rig. The sJide-in mounting bracket included with the rig is one of the slickest acts in town.

Many rigs have a front-panel layout that makes them difficult to operate in the dark. The knobs and switches on the TR-7800 are carefully shaped and placed for ease of use.

The microphone wouid need five pins to connect the ground, audio, scanning, and PTT lines to the rig, but the TR-7800 has six pins in its mike connector, leaving a spare for the inventive ham One possible application that immedia-ely comes to mind is the power connection for a touchtone7^1 mike or an autodialer. Just connect 12 volts to the spare terminal in the mike connector and you're in business!

Conclusion

The TR-7800 is one of the most carefully thought out rigs l nave ever used. Unlike many other synthesized rigs, the fancy features don't substitute for good performance. This rig s basic characteristics are beyond reproach, and Í could explain

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