[South Florida DX Association] Diversity RX

[Bill Marx]

Found on the Icom Reflector...

What to do when you up-graded to a Pro 3 with the old reliable Pro/Pro-2
rig? Diversity RX is a method where two or more receivers listen to the
same incoming signal with co-located cross polarized antennas or widely
spaced antennas of the same or different polarization. The basic idea is
that as one channel fades out the other is still working or both add to
produce a net gain. An example would be a Butternut HF-9 on one rig and
a G5RV on the other, on your headphones, the vertical is on one ear, the
dipole one the other. Does one have a better signal? Put the "Master"
rig on it via a coaxial transfer switch. Icom HF radios like the 756 can
be set up for a poor man's diversity receive system, by connecting the
CAT ports together and setting up the baud rate and address to the same
value on both radios. What happens is as you tune or change the filter
on the rig your touching, the other radio "SLAVE" follows like magic. As
you tune one rig the other follows obediently. At W7DO, I built a cool
little switch box that allows either radio to be the MASTER with
connects to my computer via the icom level converter CT-17 to my logging
program. The "MASTER" rig is the one with the active TX, also the one
connected to your Linear Amp if needed for pile-up combat. Also by
switching the "fixed" audio outputs from the detectors directly to a
soundcard, you can have the MASTER output available for other uses like
on screen decoder and O-Scope programs. Important! However, make sure
the keying is in parallel via the ACC-1 jacks in the back of the rig,
this assures both rigs go to transmit when either is keyed. Make a
jumper that connects the keying/ground pins of both rigs. This protects
the companion RX from TX damage by the active TX rig. Too scary? have a
technical friend check your handy work. You don't have to talk on or
Morse key the idle TX, just make sure the idle TX is on and not
processing an unintended signal. There's more confusion than any
advantage by trying TX diversity, at least for me.  Also, since the rigs
are essentially independent, they do not share a common xtal time base.
This will cause a slow beat note that is annoying, so press the idle
RX's TS button for full resolution and use it's RIT to correct the time
bases. What? Run the two audio channels from the two RX to a monitor
O-Scope X/Y set up for lassajou patterns and carefully adjust the
"slave" RX RIT for a steady or very slow moving ellipse. I use an old
Yaesu YO-1 scope for that. Someone is always throwing a carrier to tune
up or practice being a LID, so take the opportunity to look at the
monitor scope and correct the error. As the rigs warm up, this becomes
less and less of an arduous task. So what happens? I run the audio to a
Behringer Xenyx 802 mixer, this is a great value at $59.99, plug in a
nice headphone set and run stereo or mixed "blended" RX audio, you'll be
impressed. There is a very cool but subtle spatial effect when
conditions are stable, close your eyes, and you'll sense stations in QSO
around you in the room. It's funny that no diversity literature talks
about this effect. Too complicated? Well convince your XYL you need that
IC-7800 pronto, that does all the above. If you like fiddling with
knobs, like an old Boeing 707 flight engineer, you'll love the above.
Finally other rigs like the 775 work too, just make sure they are the
same series, this ensures the time delay through them is roughly
matched. Lastly, when running AM, make sure the carrier is turned down
on the slave. 73, Gary, W7DO "CW Forever"