Posted by
David Gilbert on
Sep 16, 2010; 8:37am
URL: http://elecraft.85.s1.nabble.com/K3-Diversity-Reception-and-Antenna-Directivity-tp5537531.html
Several weeks ago, I believe that Wayne posted a message asking what
kind of different uses people were coming up with for their K3. One
thing I've been playing with lately is feeding the signals from two
horizontally polarized antennas at different heights on my tower into
the Main and Sub receivers of my K3 in diversity mode. Since the
relative phase between the two signals is preserved in the translation
to audio, I can feed the audio from the two receivers into the A and B
channels of my computer sound card and compare the relative phase using
a dual-trace sound card oscilloscope program like Zelscope. By knowing
the vertical distance between the two antennas I'm hoping to be able to
calculate the arrival angle of the signal in real time. I say "hoping
to" because so far I don't have a distant stable, unmodulated carrier to
work with ... the best DX carriers have come from 40m BC stations but
the modulation screws up the triggering. Once I get the methodology
worked out a bit better I'll ask someone in Europe to throw a carrier on
frequency for me.
Playing around with this stuff got me thinking, though. What if I fed
the output from two VERTICAL antennas into the K3 receivers in diversity
mode, fed the audio output of both receivers into the A and B channels
of the computer sound card, and used an application that introduced an
adjustable delay in one audio channel before summing the two channels
and doing the D/A translation back to monaural audio? Wouldn't that
have the exact same effect as being able to adjust the phase of the
incoming RF, and therefore the directivity of the 2 element vertical
array? I'm pretty sure that today's computers could certainly handle
the computation. There wouldn't be any constraints on the amount of
delay so the array should be continuously steerable through an entire
360 degrees, and since the delay would be imposed digitally there
wouldn't be any frequency dependency. Ideally the two feedlines would
be of equal construction and equal length, but even if they weren't it
would be fairly easy to characterize their relative phase delay as a
function of frequency. I think mutual coupling even become a non-issue
if the verticals are non-resonant. Non-resonant antennas might be the
way to go anyway since such unlimited control over phase means that
spacing between them would be less of an issue, and therefore the same
pair of verticals could be used on more than one band as long as the
spacing was wide enough.
Why wouldn't this work? The PCM data format is pretty straightforward
and I can't believe that the application would be that complicated to
write. I must be missing something but nothing jumps out at me. If it
worked, it could even be a feature in a next generation K3 (maybe even
the current one) .... all it would take is some means to adjust the
delay since everything else (two phase locked receivers, DSP processing
for both RF and audio) is already there.
In the case of the K3, all of this would only apply to reception, of
course, although it almost seems like a transceiver could be engineered
that used the desired delay determined from the receiver to set a
corresponding delay for two identical tone-modulated transmitter chains
driven from the same oscillator. I suspect a pair of phased
transmitters would have pretty limited appeal, though ... certainly
they'd be an expensive way to get just two or three db steerable gain.
Fun stuff to think about, in any case.
73,
Dave AB7E
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