[Elecraft] [K3] Diversity Reception and Antenna Directivity

[Alan Bloom]

> 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?

Yes, I think that would work fine.  There are two issues that I can
think of:

While the main and sub receivers are phase-coherent, the actual phase
difference between them is random.  I believe that if you change
frequency it is not guaranteed that the phase difference will be the
same.  So every time you change frequency you may have to re-adjust the
phase delay to get the antenna to "point" in the right direction.

The other issue is that the antennas must be no more than 1/2 wavelength
apart to get a clean, single-lobe response in the directivity pattern.

Al N1AL


On Thu, 2010-09-16 at 01:37 -0700, David Gilbert wrote:
> 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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