[AK-VHF] which polarity is preferrws for long-range VHF/UHF/mw shots

[David Heimke]

This is a topic in the ARRL Antenna book, 15-2 in my 22nd edition.  Their
punch line is no discernable difference unless you are hearing the local
noise near the antenna which tends to propagate with vertical polarization
as we all know (the other polarizations of a ground wave attenuate quicker
due to ground resistance).  In that case horizontal would provide a weak
signal advantage.

I had an interesting experience about 30 years ago with the very early UHF
digital radiotelephone systems using TDMA so multiple subscribers could get
Basic Exchange Radio Telephone Service (BETRS) up near Central,  Alaska.
Our choice to provide basic telephone service to people too far away for an
economical cable plant installation was these new systems, point to
multipoint.  Right above our UHF band.  Vertical polarization was the
choice so that we could use one base station antenna, and then the
subscribers were typically a yagi.  Well, I couldn't get the new system to
sync up so no calls could be made.  I had to cry uncle as I could easily
make analog FM calls work on a different radio system.  The manufacturer
sent us a bright experienced tech, and we looked at the incoming signals on
a spectrum analyzer.  The levels were jumping all over the place!  Even
from visible line of sight locations. It was clearly multipath but like I
hadn't seen before, these were not mobiles.  We tried horizontal
polarization and everything quieted right down, synchronization
established, calls were solid.  I scratched my head quite a bit, but during
lunch in the local Central Roadhouse a USGS crew came in from flying over
the area (rich mining district).  They mentioned that their magnetometers
were pegging the needle, that the ground was very conductive.  I got to
thinking that maybe was why we had so much multipath.  Anyway, the
horizontal worked, we built a horizontal base station array, turned the
subscribers to horizontal, and purchased a couple "Eggbeaters" for our
telephone truck for mobile operation.

I often wondered if I could exploit that and build a UHF gold finding radio
gun......

73's,

Dave AL7LO

On Thu, Jun 16, 2022 at 3:55 PM Paul Kiesel via ak-vhf <
ak-vhf at mailman.qth.net> wrote:

>  So, if the state of affairs in a certain area is that antennas are
> vertically polarized, then it makes sense to change them to be horizontally
> polarized. Weak signal enthusiasts using vertical polarization might do
> well if they consider doing this. Gotta convince everyone to do it, though.
>
> 73, Paul K7CW / VE7IB
>
>     On Thursday, June 16, 2022 at 03:55:30 PM PDT, Ed Cole <
> kl7uw at acsalaska.net> wrote:
>
>  I thought this was an interesting answer why horizontal polarity is
> chosen as standard for weak-signal VHF and up operation:
>
> "Yes polarization is maintained under clear free space paths.
> Reflections off of angled structures can cause polarization rotation.
> Propagation through magnetically biased plasma (the Ionosphere) result
> in polarization rotation."
>
> **This is called Faraday rotation for satellite and eme signals**
>
> "Reflections off of surfaces that have the same orientation as the wave
> tend to reflect more efficiently. This is why horizontal polarization is
> preferred for paths beyond the horizon. Troposphere bending is greater
> when the waves electric field is is in the same plane as the boundary.
>
> Brian
> WA6QDP"
>
> 73, Ed - KL7UW
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