[Elecraft] [K3] Diversity Reception and Antenna Directivity

[David Gilbert]

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