I've been interested for some time in tracking the arrival angle of DX
signals, and in the past I've used the audio output of the two phase
locked receivers in my Elecraft K3 fed into a 2-channel oscilloscope
application via the stereo line input of the sound card on my computer.
Just trigger on one channel and look at the delay for the other
channel. It worked ... sort of ... and it works because phase is
preserved in the down conversion from RF to audio.
But with the availability of coding agents like Claude or Codex, I'm now
working on a browser app that does FFTs on the audio inputs from the
phase locked receivers, uses better algorithms to determine the phase
angle, and plots the result over time as a scrolling display. It has a
"phase calibration" slider to zero out phase differences in the to coax
runs, and will compute and plot the arrival angle once you tell it the
RF frequency and how far the antennas are apart. It will also have the
ability to switch between elevation angle and azimuth angle depending
upon how the two antennas are arranged. Of course the "phase
calibration" to get absolute values for angle would only work if you
provide a signal source midway between the two antennas, but otherwise
it is still interesting to be able to see the time varying relative value.
It isn't completely ready yet but should be soon. It has given accurate
results when using signals from a 2-channel RF signal generator with the
ability to vary the relative phase.
The reason I mention it now is that in testing it with the two antennas
being my 2 element Shorty-40 positioned about 10 feet above my tribander
(four elements on 20m and 15m, eight on 10m) I've noticed very large
swings in the phase difference using WWV at 10 MHz. I used a very
narrow passband (100 Hz) on the K3 in order to mostly eliminate the
modulation. I theorized that the yagis, due to having parasitic
elements, introduce their own phase delay that may be different
depending upon the arrival angle of the signal, and since the two
antennas are significantly dissimilar the amount of antenna-induced
phase difference is likely different and indeterminate. My two
antennas have not been pointed at WWV. I queried ChatGPT on this, and
it rather strongly confirmed it as being likely.
I honestly don't know how equivalent the phase difference contributed
solely by the antennas would be for two different yagis pointed at the
desired signal, or if it would be different for different arrival angles
even if the were pointed in the right dirrection, or even if it would be
different for two identical antennas at different heights due to ground
interactions. Maybe EZNEC could tell us that but I haven't looked into
that yet.
By the way, if anyone should happen to be interested, the app will be
just some HTML and JavaScript to run in any modern browser and it will
be free. Maybe I'll accept donations. ;) It will need a rig with two
receivers that can be phased locked. Or maybe just use the SDRPlay
RSPduo ($300) with the SDRuno app (free) that can pretty much do
everything by itself, and might even work my my future app for plotting
results over time.
Sorry for rambling on but I thought the part about capturing phase from
different antennas might be relevant.
73,
Dave AB7E
On 3/10/2026 2:25 PM, Jim Lux wrote:
This would assume you get enough signal to show on an oscilloscope at your
frequency of interest. And that there's no interference. Or you've got a narrow
band filter (matched) on both legs.
Some tens of millivolts, perhaps, which is ~ -30 dBm.
Just as an example, if you have a 1 Watt source, 10 km away, at 15 MHz, and
isotropes on both ends, you'll be receiving -48 dBm.
If you have a Yagi with 8 dBi gain, ok you're at -40 dBm.
And your source could be 1 km away, that would get you to -20 dBm.
You could also use any of a variety of two channel SDRs that have phase coherence. (many don't
- it they use a different LO synthesizer for each channel, so there's an ambiguity in
the "startup phase" of the synthesizer)
On Tue, 10 Mar 2026 12:05:24 -0600, Jim Rhodes<jimk0xu@gmail.com> wrote:
Best method would be a O-scope with H input to ant 1 and V input to ant 2.
Use feedline, identical length and characteristics. Feed the same low
level signal to both antennas with whatever switching you have available.
If your signals are in phase you are perfectly in phase. At the
feedpoints, if the feedpoints are equidistant from the boom. However I bet
they aren't. Cheap way. Low level signal again to both antennas use a
remote receiver at a comfortable distance. O-scope again will show 2
superimposed sine waves out of phase if they are not in phase. Now turn
the antennas to a new heading 90 degrees in same direction. I bet the
results will be different. To the dx they are going to be phased at some
random angle. Different dx, different angle. Worth the trouble? Probably
not, unless there is on heading you want to favor. BTW you can tell the
phase difference by the fraction of the wavelength difference. To tell
which signal is which add a few feet of feedline to 1 antenna.
Jim K0XU
jim@rhodesend.net
On Tue, Mar 10, 2026, 10:29 George Fremin III wrote:
I have posed this question to a number of people over the last few years -
and I have gotten some interesting ideas but I am not sure any of them have
provided a simple or repeatable way of making such a measurement. I have
not tried any of they yet but I think I am getting to that point.
So, I thought I would cast a larger net.
On the simple side of things - if I have two antennas - lets say verticals
at some distance from each other with coax coming from them is there some
way to measure the phase difference? Could I get some value out so that I
know how much delay I need to add to one to get them in phase for a given
signal?
Or lets say I have two yagis on a tower fed with coax and I would like to
verify they are in phase or at least close - can I measure this in some way?
What if I have say a 48 foot boom 10m yagi and a 24 ft boom 10m yagi on a
tower at 60ft over 30ft. If there a way for me to measure the phase
difference?
The last question is a real use case - and on the air use of this antenna
seems to show that I might have lucked into these antennas being in phase -
at least they work better together for EU and the USA. But it would be
nice to repeat this luck or measure it.
It would be nice if this did not require $100k in test equipment.
George Fremin III
K5TR
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