Re: [K3] Diversity Reception and Antenna Directivity

Posted by Alan Bloom-2 on Sep 16, 2010; 5:47pm
URL: http://elecraft.85.s1.nabble.com/K3-Diversity-Reception-and-Antenna-Directivity-tp5537531p5539646.html

Yes, that should work, just switch the sub receiver antenna over to the
main receiver to calibrate the phase.  I think you'd get the best
accuracy by looking for a null and then subtracting 180 degrees.

By the way, I think rather than an adjustable delay between the two
channels you need an adjustable phase.  (If the phases of the two local
oscillators in the K3 differ by X degrees, than all audio frequencies
also differ by X degrees.)  There are a number of ways to do that, but
probably the most straightforward is to re-convert each audio signal to
"RF" (a few kHz) using local oscillators of the same frequency but
different phases, and then convert back to baseband with a single LO.
That could be done either with hardware or in software.

Just a SMOP.  (Small matter of programming :=)

Alan N1AL


On Thu, 2010-09-16 at 10:08 -0700, David Gilbert wrote:

> Thanks for the reply, Alan.
>
> That's interesting.  I didn't realize that the two receivers in the K3
> had a random phase difference between them even when locked.  I noticed
> differences in phase delay when I changed frequencies during my tests
> with the two horizontal antennas on the tower, but I mostly attributed
> that to different arrival angles for the different stations being
> monitored, and different phase delay of the feed lines (expressed in
> wavelengths) at the new frequencies.
>
> However, that random phase difference between the two receivers could be
> adjusted out by momentarily feeding the same antenna into both receivers
> at each new frequency.  That routing could be accomplished within the K3
> if there was a quick and easy way to control whether or not the sub
> receiver was switched to the AUX RF antenna when diversity mode is
> active.  If that routing option took the form of a command, the whole
> process could be done in software (either external or internal to the
> K3) each time the frequency was changed ... albeit of course with some
> settling delay while the phase difference was determined and adjusted out.
>
> 73,
> Dave   AB7E
>
>
>
>
> On 9/16/2010 8:42 AM, Alan Bloom wrote:
> > 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.
>
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