|To:||Martin Ewing AA6E <email@example.com>, firstname.lastname@example.org|
|Subject:||Re: [TowerTalk] Re: Horizontal + Vertical Polarization Question|
|From:||Jim Lux <email@example.com>|
|Date:||Fri, 21 Nov 2003 08:56:49 -0800|
At 09:39 AM 11/21/2003 -0500, Martin Ewing AA6E wrote:
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.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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