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Re: Topband: circular polarization on 160m

To: "JC N4IS" <>, <>, <>
Subject: Re: Topband: circular polarization on 160m
From: "Tom W8JI" <>
Reply-to: Tom W8JI <>
Date: Wed, 5 Feb 2014 16:36:13 -0500
List-post: <">>
The way I see it is if the rate is not 0.546 uS or so, you do not have
circular polarization.You have a slowly rotating wave, and the sense of the RX antenna would be meaningless unless you could time-sync rotation at that
slow fading rate.

Someone correct me if I am wrong.
100% correct

I hope Carl K9LA has input, but I cannot think of a single way that a circular polarization signal would have fading that would be corrected by changing from a linear polarized antenna to a circular system. This is what perplexes me about any advantage of using a circular RX antenna based on the signal:

1.) If the wave was circularly polarized, that could not cause a fade on a linearly polarized antenna. It rotates far too fast for that. It would just be a steady 3 dB loss.

2.) A slowly rotating signal can go into fades as the electric field crosses the minimum response of an antenna. Making an antenna that responds **in a correct way**, so we don't have a skewed or sloped linear polarization (because that would still fade), might cure that fade. The cure would always be at a S/N penalty for half of the rotation or more. The tradeoff would be a few moments large advantage (during the fade) for a longer time disadvantage. If the horizontal antenna did not have comparable directivity to the vertical, that system could "totally hose" S/N for all but a very short time, that time being when there would have been no signal.

3.) On VHF, and even ten meters, we can build a directive vertical and horizontal antenna with a good pattern at low wave angles. The wavelength is short enough we can get away from noise, the earth, and have low angle horizontal patterns. But.....a linearly polarized antenna would not fade to zero from a rotating wave unless it was rotating slow. The period of rotation for a circularly polarized wave is far too fast for that. I can tune into FM BC circularly polarized signals with linear polarized antenna, either a dipole or vertical, and not have a bit of fading. Any fading would only come from my having the wrong rotation on a circular receiving antenna, or a long term null of response from a very slow rotation.

This is what perplexes have fading from polarization it has to rotate slow. That is not a circularly polarized wave by the normal use of the term. If the wave rotates slow, the R-H L-H sense of the antenna makes no difference at all.

So why are experimenters hearing slow fade on a linear antenna, and correcting that fade ONLY with a certain L-H or R-H antenna? It was rotating fast enough to be circular, the antenna rotational sense would make zero difference and it would not be fading on a regular single polarization antenna. The wave rotation would, at best, only cause a 3 dB fade into a linearly polarized antenna.

This gives me pause about what people are measuring and writing. If they are correct, hundreds of FM BC transmitters need to change their antennas. We have a WA3 claiming the rotational direction makes a difference, that implies the wave is circular. But if the wave were circular, he would not have fading on a linear antenna.

73 Tom
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