I did a simple simulation to get the "difference in phase between two antennas"
as a function of incoming elevation angle.
I assumed 20 meter wavelength, 10 meter antenna height, and two configurations,
one where the second antenna is 5 meters higher, the other where the second
antenna is 5 meters horizontally displaced, in the direction of propagation.
And for 4 reflection coefficients: -1 - (typical for low angle H-pol), -0.5
(lossy version of previous), 0 (no reflection), and +1 (flipped reflection
phase)
Here you go - I can post the matlab code if anyone wants it.
https://drive.google.com/file/d/19LO0YacHbloWAfboGQq_3SmFTWrBKXtE/view?usp=sharing
There was a bug - the incremental phase between the two antennas just due to
displacement is partly wrong, but the general shape of the responses should be
ok.
If Dave posts his frequency, height, and spacing, I can run it for that.
On Tue, 14 Apr 2026 13:30:22 -0700, David Gilbert via TowerTalk
<towertalk@contesting.com> wrote:
I decided that the SVG version of the moving interference pattern I
previously linked had some flaws. The motion was at a constant rate and
the direction of the motion of the combined diffraction pattern should
have been in any direction. Codex had difficulty resolving those
problems within SVG so after many iterations I told it to switch to a
Canvas implementation within JavaScript/HTML. I think the result is
much more accurate and is located here:
http://www.ab7e.com/Interference Pattern.html
Notice that the red and green arrival angle lines now shift in phase
relative to each other in sync with the displayed phase shift ... which
also now goes both positive and negative.
The interference pattern of the combined waves is now the much broader
shaded light colored pattern and it now shifts in multiple directions.
The is a more accurate display compared to the SVG version ... which
turned out to be more illustration than representation.
A really key point is the comment made by Gemini (another AI agent) that
my good friend Bob, K7ZB used to analyze what is going on. And that is:
What we really measure when we compare the phase of the signals from two
antennas is the instantaneous GRADIENT of the interference pattern that
results from multiple signal paths (both relative angle and relative
phase) due to propagation and various local reflections (ground, nearby
terrain, other structures).
Not sure if anyone else finds this stuff as interesting as I do, but at
least it explains what I empirically found when trying to use my
ArrivalAngle application.
73,
Dave AB7E
p.s. For reference:
(http://ww.ab7e.com/ArrivalAngle.html).
(https://youtu.be/MxRaYSRMPE4)
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