Hi James, Yes, multipath is certainly a variable, and I'm actually trying to include something that's not outwardly obvious regarding the directional response of a receive antenna related to polarization versus vertical polarization which is something I had never before considered (I'm not trying to exclude anything), and I don't recall it being discussed before. I suspect the signal is changing polarity frequently (probably rapidly) and probably often appears like circular polarization, etc. so it's a very complex picture.
Thanks, Don (wd8dsb) On Thu, Jun 3, 2021 at 12:57 PM James Wolf <[email protected]> wrote: > Don't dismiss the possibility of multipath reflections. > > Jim - KR9U > > > > > -----Original Message----- > From: Topband [mailto:[email protected]] > On > Behalf Of Don Kirk > Sent: Thursday, June 3, 2021 9:10 AM > To: topband <[email protected]> > Subject: Topband: Interesting observation and comment (Skewed Path Vs. > Horizontal/Vertical Polarization) > > 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) _________________ Searchable Archives: > http://www.contesting.com/_topband - Topband Reflector > > _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
