Preview of Kenwood’s latest OSCAR rig.
This entry into the goodies available to the increasing number of OSCAR 13 operators has stirred up a lot of enthusiasm and anticipation Although I had read all of Kenwood’s magazine advertisements and press releases. I had yet to see a unit, much less enjoy the opportunity to operate one from my own shack.
I am fortunate in having available an extensive complement of laboratory-grade instrumentation as a result of an earlier venture in manufacturing ham UHF and VHF equipment. Consequently, I always feel certain that the gear in my ham shack is at the peak of performance. I spend much more time tweaking and updating than I do operating. Now, I was about to have a chance to see how close a box manufactured many thousands of miles across the sea could come to approaching the performance of the satellite equipment that I treal with such tender loving care. There was no question in my mind that a single, multi-band transceiver had to be inferior to the installation of receivers, converters, transverters. preamps, linear amps, power supplies, etc., that constitutes my OSCAR station.
As I unpacked the neat and compact transceiver, I became even more convinced that it would have to run a poor second in performance to my accumulation of satellite hardware. Anything that could be packed this compactly must have lots of design compromises and performance tradeoffs!
I don’t think I’m unique when it comes to getting a new “toy”: I want to make it play at once. I can always read the Instruction Manual later, when the band is dead. Sometimes I want to skim through the manual briefly to orient myself, but the main objective is to connect the power supply and the antenna and “make like a radio ham.”
With this radio you cannot follow this routine! You’ll have to STUDY the Manual to operate the features of this radio. The 790A is really three transceivers, each with three operating modes.
After several hours of reviewing the instruction manual, I later felt qualified to do more than work 146.52 simplex, but I was still hazy aboul using some of the more complex features.
General Operating Features
It’s very difficult to describe ail of the many operating features of this remarkable transceiver. Only a “hands-on” examination will let you appreciate the intricacies of the design.
First of all the front panel’s 43 switches and rotary controls are intimidating enough even before you realize that a majority of them serve different functions, depending upon the chosen position of some of the others. Unfortunately, even after intensive study of the manual, some of the interdependence of these controls is not apparent
From the operator’s viewpoint, the 790A consists of three multimode transceivers. At any given tnstant you can listen on two different bands with independent selection of mode, tuning, squelch threshold, volume, etc. One of these two is designated as the “MAIN” receiver, while the other serves as the “SUB” receiver. A single panel switch lets you reverse the two. The principal operating difference is that the MAIN unit also functions as the transmitter. The SUB Receiver will continue to serve its selected functions regardless of the current mode of the MAIN unit. The frequency of either unit can be tuned without affecting the other The only limitation is that the MAIN and the SUB may not be on the same band.
The selected status of the MAIN and the SUB sections can be exchanged at any instant by means of the main/sub function key. Each section has an A and B VFO. selectable at will Either active section can be switched to operate from any one of 59 programmed memory frequencies: all attributes of mode, offset. CTCSS, etc., are retained in memory. Flexibility of frequency, mode, offset, tone, squelch, audio volume, etc.. is virtually unlimited. I don’t have the time or the space here to include all of the many more things that you can do with this unit!
Although the TS-790A can fully service the operating needs of any VHF/UHF/microwave enthusiast, it will probably appeal principally to the ham who operates (or plans to operate) using the OSCAR, UoSAT, JAMSAT and RS Satellites Unfortunately, the unit I received to review did not have the optional 1200 MHz module, UT-10. So, I was unable to put it through its paces on OSCAR 13, Mode L
I was. however, able to do all of the other exciting things provided by both OSCAR 10 and OSCAR 13 on Modes B and JL In addition, I had two OSOs with Alexander U4MIR, on the Russian MIR space platform. All this in just a few days!
Automatic Down Link Frequency Finder
One of the problems that I have had with my present equipment has been the need to set my separate receiver and transmitter to the appropriate uplink and downlink frequencies, corrected for Doppler and the round trip time delay. The TS-790A neatly solves this by allowing you to program into memory the appro* pnate numerical value representing the sum of the uplink and downlink frequencies, a constant for each of the satellites. You can store and retrieve this number for as many as ten different transponders, then just tune the SUB receiver to the desired frequency and push the sat key This will automatically move the MAIN unit to the appropriate transmit frequency. Alternatively, you can set the MAIN section to the desired transmit frequency first, and then push the sat key. The SUB receiver will automatically move to the appropriate down link frequency. I am certainly going to miss this capability when I have to relinquish the 790A and am forced to do it the hard way again.
I found only one area where the transceiver needed help. On both 2 meter and 70 centimeter operation, the input signal required to activate the S Meter was far in excess of the level of signals received from existing Phase III satellites. This is not necessarily a bad thing because, except for installations with very short feedhnes to the antenna system, you’ll want to install a preamp at or near the antenna.
In my specific installation, the GaAsFET preamplifiers determine the system noise floor. With these in line, the TS-790A S Meter is indeed quite comfortably scaled. Incidentally, the MAIN section has a conventional analog meter for signal strength display, while the SUB section boasts a very fine resolution LCD display for signal strength. I was pleasantly surprised to measure the actual noise-floor of the receiver on both 2 meters and 70 cm at about 0.019 fV (for3 dB S + N/N). Adding my GaAsFET preamp improved this by about 2dB to 0.015uV,
Power output on both bands was in excess of that specified by Kenwood. I was initially surprised at the specified higher output ratings for the FM modes vs. the SSB modes. Presumably this is a function of linear range vs, saturation operation for FM. The unit employs multi-stage “bricks” for all the RF Power stages on both 70 cm and 2 meters, and as the driver stage on 1200 MHz. A discrete bipolar transistor serves as the 1200 MHz PA.
Early in this article I expressed my doubts regarding the ability of a package as compact and attractive as the TS-790A to have the capability to compare favorably with a multi-component dedicated satellite assembly of equipment. I can now say that my doubts were unfounded. Other than the definite desirability to add external low noise preamps, this unit matches my equipment across the board. And the XYL might let me bring a package this attractive up from the basement “studio”!
I have only one major concern about operation with transceiver-type multiband equipment. You must be very, very careful to never activate the transmit function on the band where you have your receiving preamplifier, or goodbye. GaAsFET. Once you’re comfortably familiar with the MAIN and SUB sections of this unit, this situation shouldn’t be too high a probability. But, I nearly did it twice. Fortunately the MAIN was in the SSB mode with the microphone gain all the way down. Whew!
I have neglected to say as much about the FM operation and the many scanning features as the radio deserves.
– 1989 Ed Clegg W3LOY – 73 Amateur Radio