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Re: [TowerTalk] Re: Horizontal + Vertical Polarization Question

To: Martin Ewing AA6E <>,
Subject: Re: [TowerTalk] Re: Horizontal + Vertical Polarization Question
From: Jim Lux <>
Date: Fri, 21 Nov 2003 08:56:49 -0800
List-post: <>
At 09:39 AM 11/21/2003 -0500, Martin Ewing AA6E wrote:
K9OM asks:

Has anyone experimented with feeding both a horizontally polarized and
vertically polarized antenna simultaneously on HF? Such as, feeding a horizontally polarized yagi and a vertical on 20, 15, or 10 meters?

Well, in my time, we called this circular polarization. That's what you have if you feed H and V 90 degrees out of phase, anyway, and if the phase centers of the two antennas coincide. If the antennas are not symmetric, you'll get elliptical polarization, i.e., circular plus linear. If the antennas are physically offset, you'll get "interesting" interference fringes on top of the normal radiation pattern.

Circular polarized antennas are insensitive to the (linear) polarization angle of the incoming wave, so that eliminates one source of QSB. (Propagation can twist the polarization angle, but typical HF propagation favors H polarization. It's the same reason your Polaroid sunglasses work.) On the other hand, a right-hand circular antenna rejects left-hand circular waves, so if both sides are playing this game, you'd better agree which sense to use. The optimum antenna (on receive, but same argument for transmit) for a linearly polarized wave is linearly polarized at the same orientation. If you use circular receive for a linear transmit, you are going to be down 3 db against an optimum linear antenna. So there's no free lunch.

I think, though, that given the random polarization of the incident wave when it actually hits the antenna(especially given all the stuff around the typical ham antenna.. relatively few of us have antennas on tall non-conductive towers, fed with optical fiber, over perfectly flat salt water marshes, etc.), the fact that most CP (or, more properly elliptical polarized) antennas have no deep nulls when receiving a LP signal is significant. Sure, you lose 3dB on the peaks, but you also don't get the 20-30 dB fade when the signal happens to be cross polarized. (one reason why TV stations broadcast CP/EP.. it keeps multipath fades from being so deep)

It would be very interesting(!) if someone were to actually measure the incident polarization of typical skywave signals (actually, someone probably has.. the radio astronomy folks working at HF have to deal with nulling out interferers, etc., and I'm sure some one in the SW broadcast business has looked at this), particularly in terms of the short time statistics.

If someone could suggest a simple way to do it, I might do it myself. Perhaps a couple of short dipoles, fed through a FET switch, to a receiver like the PCR1000 hooked up to a PC for data logging? Flip the switch 10 or 100 times a second, etc. I could even look at the NCDXF beacons or, perhaps something like WWV/WWVH. Shortwave broadcast might be a good source of a transmitted signal at a known frequency and time.


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