I ran my K3 in diversity mode during the ARRL 160 meter contest for the first
time from this side of the country. It was a revelation. If you've never
listened in diversity, you must do everything you can-- now that we're in the
time of year that's favorable for the low bands-- to experience this for
yourself. Top Band here in the Eastern Time Zone is a lot more fun that it was
on the west coast.
The K3 Owner's Manual describes diversity mode like this: "True diversity
requires a pair of identical receivers running from a common frequency
reference and using two different antennas." Where you connect your two
antennas depends on whether you have the antenna tuner and transverter board
options, but you should configure the transceiver to accept the dedicated
receiving antenna at the AUX input because there's a bit less loss at this
input.
You enter Diversity mode with a long press of the SUB button. Usually, your
main (transmitting) antenna is fed to one ear and the receive antenna to the
other ear by setting "L-MIX-R = A b" in the K3's CONFIG menu. It also helps
to set "SUB AF = BALANCE" so that you can use the SUB audio control on the
front panel to make the two antennas sound equally loud in your headphones, in
conjunction with adjusting the RF gain of each antenna from the front panel. I
believe the best practice is something like the following:
* While listening to noise adjust the RF gain controls for 'an equal amount of
noise' from the two antennas
* Then listen to a signal and use the SUB (Balance) control to equalize the
levels and place the signal in the center of your stereo headphones
Who would have thought that an antenna laying on the ground would be useful,
but this year I tried a loop on ground (LoG) antenna as the 2nd antenna. The
LoG was a square only 20 feet (6.1 m) per side, made of insulated wire, in
contact with the ground, and fed at a corner with a 9:1 transformer wound on a
binocular #73 core. This is the common LoG design that you see all over the web
( http://kk5jy.net/LoG/ ). The LoG is somewhat bi-directional for low angles of
arrival, so I oriented it northeast-southwest. I got the best results by:
1/ Using an antenna tuner to better match the LoG to the 50-ohm input of the
K3. A LoG has very high loss, so everything you can do to conserve its signal
power helps. I noticed an S-unit of LoG receive improvement when using the
tuner.
2/ Turn the preamp on for the LoG, but the attenuator on for your main antenna.
3/ Route the main ant to your left ear and the LoG to your right, as discussed
earlier.
4/ Because my LoG was directly under the transmit antenna, and even though I
possibly could have done without one, I was more comfortable with a PIN diode
switch to protect the AUX input (which is where the receive ant enters the K3).
I built a circuit that takes the KEY OUT of the K3 and switches a bias voltage
to the PIN switch: +12 V on receive and -12 V on transmit. This switch has a
measured isolation of > 60 dB... good enough for transmitting at 100 W and
probably much more. However, this might have been overkill and a simple diode
limiter probably works just as well.
Using the RF gain and Balance controls, you can center a signal in your
headphones as discussed earlier. Pretty soon you'll have a soundstage between
your ears where signals seem to float from left to right and back again as
fading and polarization occur. It's as if your head is inside the band. It's a
very powerful psychoacoustic experience that gives you a visceral feel for what
propagation is doing. Instead of fading in and out, signals move from left to
right and back again, sometimes slowly, sometimes abruptly, always randomly.
My main ant being a horizontal dipole, I was pleased that when a signal would
fade *out* on the main, it tended to fade *in* on the LoG, and vice-versa. The
end effect of this is that you largely mitigate QSB. Signals stubbornly hang in
as the band does its fading thing.
Since the contest, I've tried the LoG on 80 and 40 and it works even better on
those bands. Since your main ant's RF gain is cranked way down to match the
LoG's output, everything sounds quieter. I found myself wondering why my noise
level was so low. But don't worry, you'll still have enough sensitivity. The
noise floor is so low that you feel as though you can copy signals down to
negative infinity. The effect is addicting!
If your K3 or K4 has a subreceiver, I urge you to try diversity mode. I think
you'll be delighted at what you hear.
Al W6LX/4
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