Topband: circular polarization on 160m

[Tom W8JI]

Hi Carl,

This has to be the big picture of the system and the goals, and not a narrow 
picture of what a wave is doing.

I think in the big picture we all agree it is useless.

> First, when I said "advantage", all I meant was there is less fading on HF
> when receiving on a circularly polarized antenna. That's the common
> conclusion of those "studies" that I referenced. Remember these studies 
> are
> HF (80-10m), not MF (160m).

While G2HCG likely had circular polarization on ten meters, there isn't much 
in the WA3's article that actually convines me he was observing  circular 
polarization. If he did have circular polarization, which he probably did 
have some, it was only basically "straight up".

This is entirely different than circular polarization at modest or low 
angles, which is terribly difficult on any lower band. To be circular 
polarized at modest to low angles, the horizontal antenna would have to 
somewhat high above ground and broadside to the DX, and the vertically 
polarized antenna would have to cross the center line of that antenna, or 
have some planned offset.

In other words, it would have to actually be a circular polarized antenna.

EZNEC actually provides a way to look at this. At the bottom of the arrow 
tabs is Desc Options. Click on that, a choice of fields appear that includes 
"circular". The bottom choice, "Linear, Maj, Min", gives a relative 
comparison of circular to linear. Do a Far Field plot and look in the FF Tab 
on the left for a level comparison between linear and circular fields.

I've seen several enthusiastic studies where a lot of time was spent with an 
antenna that really could not measure what the experimenter concluded he was 
measuring.

> Second, polarization is not purely random. There is more order to
> polarization that we generally think due to the ionosphere being immersed
> in a magnetic field. What's important is where the wave enters and
> exits the ionosphere - and how well the polarization of the ordinary and
> extraordinary waves that propagate thru the ionosphere couples to the
> polarization of your antenna. In my mind that theory translates nicely to
> the real-world. One of G2HCG's conclusions from his 10m study unwittingly
> confirmed magneto-ionic theory. I don't think he was even aware of the
> effect of a magnetic field on a plasma, so that makes his conclusion all
> the better. Yes, the ionosphere is dynamic and varies over the 
> short-term -
> so there is some randomness imparted on the what the ionosphere dictates.
> For the record, G2HCG's conclusion referenced above stated that "It was
> immediately apparent that the number of hops to the ionosphere and back 
> was
> totally irrelevant. The polarization of signals must therefore be
> controlled by the last hop."

The first issue is actually creating a circularly polarized antenna at a 
useful angle that does not deteriorate signal-to-noise. I think that is a 
very difficult thing to do unless the target is nearly straight up. Most 
people think grabbing any horizontal antenna and delaying or advancing phase 
90 degrees aganst something vertical produces a circular polarized antenna 
in any direction at any angle. Nothing is further from the truth.

A poorly planned antenna might do that in some directions or at some angles 
in some directions (with or without the 90 shift), but it will also result 
in pattern tilt and pattern change. Adding signals and noise unpredictably 
is not a good thing to do. Even if we somehow manage to improve absolute 
signal level, we can also easily "improve" noise level just as much or more.

I haven't looked at higher bands, but on 160 through 40 adjusting for some 
optimum mix largely appears to be either a random thing or useless. On most 
of HF, at least where I have looked, the same.

> Having said all the above, I still say circular polarization on 160m would
> not be beneficial due to just the ordinary wave being useful.

The bottom line is we are S/N driven on HF, not absolute signal level.

What ratio of V to H signal levels do you expect, Carl? What direction is 
the rotation? I'm assuming this is actually a circular signal, and not 
something rotating very slowly that is causing fades?

73 Tom