Wideband FM QSOs
January 22, 2005
Clint, KA7OEI, with the WFM 10 gig
setup. Click on picture for a larger version.
Most activity on the 10 GHz band is undertaken using Gunn
These units are self-contained transceivers, capable of both transmit
receive at the same time by virtue of the fact that the transmit
is also the receiver's local oscillator.
It should go without saying that one cannot receive on the same
as one is transmitting, so a standard IF (Intermediate Frequency)
of 30 MHz has been chosen. While this frequency could be
anything in the HF or low VHF range, 30 MHz was chosen because it is
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
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
MHz but nowadays, every available slot on the FM band is used.
On 10 GHz, two types of Gunn transceivers are commonly used:
The so-called "Gunnplexers." This is a brand name, but it
refers to the fancier gunn transceivers that not only have a mixer
but can be electronically tuned using a built-in varactor. This
tuning allows 50-100 MHz of frequency adjustment allowing tuning and
of either of the two standard wideband FM frequencies.
Microwave "door openers." These typically have a mixer
do not have electronic tuning. Fortunately, varying the Gunn
(typically from 7 to 9 volts for 10 GHz Gunn sources) will also vary
frequency by 5-15 MHz, the precise amount depending on a number of
While this is enough to allow modulation of the transmitted signal, it
does not allow tuning between the two standard wideband FM frequencies
so, unless test equipment is at hand, the mechanical tuning screw
be accurately adjusted to another frequency.
There are also some types of door openers that have appeared
that do not
have a mixer diode: Ron, K7RJ was looking at one of these, trying
to figure out how they could possibly work, until he realized that the
circuit extracted the mix frequency from the Gunn diode itself:
the return signal (or a received signal) actually superimposes itself
the Gunn voltage supply line. Preliminary tests indicate that
this scheme works, it does not result in as good as sensitivity as
a mixer diode, but it is possible that further refinements (such as
L/C networks in series with the power supply lead, better receiver
matching, amplification, etc.) may be able to improve performance.
Top and Middle: The
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.
test equipment) during the contest:
At the time that we did this, my Gunn transceivers were of the "door
opener" type, being Solfan
manufactured in the late 1970's and used, until the mid 80's, in the
Hamburger restaurant in Bountiful. Not having a varactor diode,
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
Owing to the cold temperatures, my Gunn transceiver drifted up several
MHz, putting the intended calling frequency of 10250 MHz (paired with
MHz) outside its tuning range. Fortunately, I'd brought along a
With the transverter's wide range IF capability, I was able to
a signal at 344 MHz that, when put into the transverter, caused it to
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
Gunn transceiver at will to verify that I was actually on the intended
frequency - something that came in very handy,
when I worked others whose Gunn oscillators had also drifted off
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
the Gunn Transceiver:
Dale, WJ7L, near-ish Joe's Rock on Wasatch Blvd (a distance of
Ron, K7RJ, on the traverse range between Utah and Salt Lake
distance of approximately 15.5 miles.)
Charlie, N7MLD, who was above the Utah State capitol (approx.
and later moved to the International Center, near the airport (approx.
I was also able to hear John, K7JL, (approx. 12 miles) but he was
to hear me. It was clear, from the sound of the signal, that
was ground obstruction at my end. Later, I moved about 100 feet
the east to clear this obstruction, but some unknown problem seemed to
stop his Gunn transceiver from working. (I could work Ron from
location, but I neither Ron or I could hear John at that point.)
After the majority of the activity had subsided, I went to Ron's
above Draper to see his setup. From there Ron continued to work
N7MLD from various grid squares in Davis county (including DN41 and
on 10 GHz, with the longest distance being approximately 45
Even at this distance, good signals were noted "horn-to-horn" (e.g. no
dish on either end.)