Wideband FM QSOs using Gunn transceivers
January 22, 2005

Clint, KA7OEI, with the portable 10 gig WFM setup.
Clint, KA7OEI, with the WFM 10 gig setup.
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Most activity on the 10 GHz band is undertaken using Gunn transceivers.  These units are self-contained transceivers, capable of both transmit and receive at the same time by virtue of the fact that the transmit oscillator is also the receiver's local oscillator.

It should go without saying that one cannot receive on the same frequency as one is transmitting, so a standard IF (Intermediate Frequency) of 30 MHz has been chosen.  While this frequency could be practically anything in the HF or low VHF range, 30 MHz was chosen because it is still in the HF range, but low enough that the mixer diode's output is still good.  An additional advantage is that there are not usually any strong signals present at or near 30 MHz.  In the past, initial activity was carried out on the bottom end of the FM broadcast band, at about 87-88 MHz but nowadays, every available slot on the FM band is used.

On 10 GHz, two types of Gunn transceivers are commonly used:

Another view of Ron's setup, above the valley fog.
Ron, K7RJ, working Charlie, N7MLD on 10 GHz WFM
Top and Middle:  The vantage point of Ron, K7RJ, above the valley fog.
Bottom:  Ron, working N7MLD in DN31 from the traverse range above Draper.
Click on picture for a larger version.

Using the transverter (as test equipment) during the contest:

At the time that we did this, my Gunn transceivers were of the "door opener" type, being Solfan units manufactured in the late 1970's and used, until the mid 80's, in the Dee's Hamburger restaurant in Bountiful.  Not having a varactor diode, I'd tuned the one that I take with me in the field to 10250 MHz, relying on the fact that everyone else was either on 10280.

During the contest, the transverter proved to be extremely useful.  Owing to the cold temperatures, my Gunn transceiver drifted up several MHz, putting the intended calling frequency of 10250 MHz (paired with 10280 MHz) outside its tuning range.  Fortunately, I'd brought along a service monitor.

With the transverter's wide range IF capability, I was able to generate a signal at 344 MHz that, when put into the transverter, caused it to emit a signal at 10280 - the receive frequency when using a 30 MHz IF (while transmitting at 10250.)  Using this scheme, I was able to retune the Gunn transceiver at will to verify that I was actually on the intended frequency - something that came in very handy, especially when I worked others whose Gunn oscillators had also drifted off frequency.

From my location (along Utah highway 111, in line with 6200 south) I was able to work most of the others that were on 10 GHz that day using Wideband FM on the Gunn Transceiver:

After the majority of the activity had subsided, I went to Ron's location above Draper to see his setup.  From there Ron continued to work Charlie, N7MLD from various grid squares in Davis county (including DN41 and DN31) on 10 GHz, with the longest distance being approximately 45 miles.  Even at this distance, good signals were noted "horn-to-horn" (e.g. no dish on either end.)

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