Topband: Interesting observation and comment (Skewed Path Vs. Horizontal/Vertical Polarization)

[David Olean]

I saw the same thing all the time on 144 MHz using my horizontal yagis, 
while trying to work vertically polarized stations. (usually mobiles 
with vertical whips.)  My yagis would always peak up the vertically 
polarized stations well off the correct heading.  The effect was more 
noticeable when the mobile was close by.  Over paths longer than say 150 
miles, the error was not visible. Headings tended to be correct.

Dave K1WHS

On 6/3/2021 9:09 AM, Don Kirk wrote:
> While playing around with my portable flag that I designed for MF/HF radio
> direction finding, I noticed something that confused me for about a year,
> and I finally figured out what's going on which led me to think about the
> 160 meter skewed path comments I've seen over the years and wonder if some
> of the observed phenomena is really Vertical versus Horizontal polarization
> of the received signal and not really a skewed path.
>
> There is a local 10 meter beacon that uses an attic dipole and my portable
> flag as well as my tuned and untuned direction finding loops always
> indicate the signal is located approximately 350 degrees from my QTH
> whereas I know this is not correct.   The beacon WA4OTD is actually located
> 8.6 miles away at a heading of 267 degrees (I'm almost 90 degrees off from
> the correct herading).
>
> Then a few weeks ago I noticed that when my good friend Jay (W9TC) was
> operating on 20 meters that my portable flag did not point in the correct
> direction of his house, and he's located 2.8 miles from my QTH and he uses
> horizontal beams on 20 meters.  I then orientated my portable flag so it
> was horizontal versus the normal vertical orientation that I use, and
> "bingo" the portable flag now indicated the correct direction.  I then went
> back and obtained a heading on the WA4OTD beacon on 10 meters with the
> portable flag orientated horizontal, and now it points the correct
> direction (mystery solved).
>
> I then went and looked at various antenna models using 4NEC2 in which I
> looked at the vertical gain versus horizontal gain of the antennas when
> mounted in their normal orientation, and this explained what I was seeing.
> Small loop antennas mounted vertical have a maximum horizontal gain that's
> shifted 90 degrees from the maximum vertical gain direction.  I then
> modeled beverage antennas and their maximum horizontal gain is shifted 45
> degrees from their maximum vertical gain direction.
>
> I suspect the polarization of received signals on 160 meters is constantly
> changing, but wonder if the skewed path observations over the years
> indicates the polarization of the received signal has shifted to
> predominantly horizontal versus vertical or a mix of both?  Maybe a crazy
> thought, but thought I should share my observations with the topband group.
>
> I've not really had a problem tracking down typical local noise sources on
> MF/HF using my portable DF antennas orientated for vertical polarization,
> and that confirms the many comments that local noise on MF/HF are typically
> propagated vertically, but thought my observation was very interesting and
> it unlocked a year long mystery about the local signals that were
> intentionally transmitted using horizontal polarization that did not track
> well with DF gear that normally does a phenomenal job.
>
> P.S. it took me a while to figure out how to look at vertical gain versus
> horizontal gain using 4NEC2, but it was sure worth the effort.  Normally
> 4NEC2 displays total gain.
>
> Just FYI, and can't wait for the comments to come flooding in about my
> crazy idea :)
> 73,
> Don (wd8dsb)
> _________________
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