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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