[Elecraft] K3 diversity phase drift
Alan
n1al at sonic.net
Thu Apr 9 18:09:12 EDT 2026
Hi Dave,
> I'm not sure yagis work so well for this sort of thing.
I imagine it would be similar to making a circularly-polarized antenna
using two identical perpendicular yagis on the same boom fed 90 degrees
out of phase, which is sometimes done at VHF/UHF. Signals coming in
off-axis have an elliptical polarzation rather than perfectly circular.
One thing to watch out for, both for dipoles and yagis, is feedline
radiation. The feedlines should be routed perpendisular to the
elements of both antennas and there should be choke baluns at the
feedpoints. Also any mast should be located out of the near field of
the antenna. For a yagi, that implies using an extra-long boom that
extends some distance behind the reflector where the mast is attached.
Admittedly hard to do at HF.
> I literally did not write a single byte of the actual code myself.
Ah, the brave new world of AI! Fortunately I retired before my coding
skills became obsolete. :-)
Alan N1AL
On 4/9/2026 9:01 PM, David Gilbert via Elecraft wrote:
>
> Hi, Alan.
>
> Yes, that could rather easily be done. Of course it's not possible to
> independently assign "phase" to an individual signal since that would
> require some sort of independent phase reference, but the app I build
> already measures the relative phase between them and that is all that
> is needed. The app also already measures the relative amplitude
> between the two signals, so it should be possible to have an app
> (either this one or a similar one) do exactly as you propose.
>
> I'm not sure yagis work so well for this sort of thing. Yagis operate
> by manipulating phase, and some of my tests involving the two yagis on
> my tower instead of the purpose-built horizontal dipoles gave REALLY
> squirrely results. I have some EZNEC models of various yagis and when
> I look at the far field data under the "FF Tab" the phase is
> dramatically different for different elevation angles. As best I can
> tell, that means that the incoming phase would be corrupted by the
> antenna itself and almost certainly in a different manner for a
> horizontally oriented yagi than a vertically oriented yagi. I suspect
> that two crossed dipoles would be best. If I remember correctly, a KL7
> did a bunch of work tracking polarization shifts a few years ago. I
> don't remember his callsign but he's pretty active on the TowerTalk
> reflector.
>
> Again ... I haven't waded this far into the swamp before so I'm mostly
> in "explore" mode as far as capturing all the nuances.
>
> By the way, I wrote the app using a PowerPoint diagram for the layout
> of the user interface and a list of prompts on what I wanted the app
> to do. I fed that into Codex and I've spent maybe 5X more time
> working on the video describing the app than I spent with Codex
> refining it. I literally did not write a single byte of the actual
> code myself.
>
> 73,
> Dave AB7E
>
>
> On 4/9/2026 12:41 PM, Alan wrote:
>> Hi Dave,
>>
>> Have you given any thought to using this technque to measure the
>> polarity of the incoming signal? One receiver input would go to a
>> horizontal dipole and the other to a vertical dipole, with the two
>> dipoles co-located (feedpoints at the same location). It could also
>> be done with two Yagi antennas mounted on the same boom.
>>
>> If you can measure the phase of each signal as well as the amplitude,
>> the polarity can be calculated with a little trigonometry.
>>
>> This is something i've wanted to do for years "when I get time". :-)
>>
>> Alan N1AL
>>
>>
>> On 4/9/2026 6:43 PM, David Gilbert via Elecraft wrote:
>>>
>>> Hi, Mike.
>>>
>>> I haven't done any searching, but I'm sure that such studies have
>>> been made ... probably many decades ago. A good friend of mine
>>> told me that a long time ago he was a consultant for the Army on a
>>> project that used an array of several antennas to track
>>> instantaneous changes in arrival angle using phase determination. He
>>> said that significant changes could be seen in fractions of a
>>> second, but I wouldn't be surprised if they were also experiencing
>>> multipath diffraction patterns.
>>>
>>> In my case, I think several factors are at play. I'm using two
>>> short (non-resonant) horizontal dipoles 18 feet high spaced about 12
>>> feet apart that are both broadside to WWV, and I'm using a really
>>> narrow bandwidth on the K3 to filter out the sidebands so I get only
>>> a mostly clean carrier. Given the results I see, I think these are
>>> the possible effects:
>>>
>>> 1. Simple multipath reflections due to ionospheric propagation
>>> effects.
>>> 2. Reflections from the sloped ground beneath the antennas (I live
>>> on a hillside) that would have different effect with different
>>> arrival angles ... AND different effect caused by #1 above.
>>> 3. Reflections from surrounding terrain. I not only live on a
>>> hillside with a mountain range to the south and west of me, but
>>> there is a deep (50 foot deep, 120 foot across) ravine roughly 100
>>> feet to the south of the two dipoles.
>>>
>>> I don't think it is possible to accurately model any of that unless
>>> it was possible to actually measure and plot a ground conductivity
>>> profile of the entire area that would show where the actual RF
>>> ground plane is. The sides of that ravine show how variable the
>>> earth is here ... soil in some places, iron-based rocks in some
>>> places but limestone or quartz in others, and rocks varying from the
>>> size of an orange to the size of a garage.
>>>
>>> I have to admit, though ... even if I can't get unambiguous numbers
>>> for arrival angle, the application accurately displays the relative
>>> phase between the signals that are coming from the two dipoles and
>>> it's rather fascinating to see the rapid and significant changes
>>> over time.
>>>
>>> The application may be better suited to displaying the azimuth angle
>>> of a signal ... presumably using vertical antennas. I suspect that
>>> there is less multipath propagation azimuth-wise than there is
>>> elevation-wise ... but I could be wrong about that as well. ;)
>>>
>>> 73,
>>> Dave AB7E
>>>
>>>
>>>
>>> On 4/9/2026 10:18 AM, Michael Carter via Elecraft wrote:
>>>> Hi Dave,
>>>>
>>>> I've been interested in your experiments since you first posted
>>>> news of them and the app you developed for angle-of-arrival
>>>> estimation. Your latest post really piques my curiosity. Is there
>>>> new science to be uncovered for the effects you describe as
>>>> anomalous, or is there professional academic literature that
>>>> already has reported such effects? I have not ventured into that
>>>> literature, but would be surprised if some ionosphere scientists
>>>> had not conducted similar experiments.
>>>>
>>>> Thanks for a very interesting thread, and keep the reports coming!
>>>>
>>>> 73,
>>>> Mike, K8CN
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>>
>
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