Antenna Polarization Information

This explains some of the signal loss issues between mismatched polarity between the signal and the antenna. My understanding is received signal polarization can change due to satellite tumbling and it can change as it passes through the ionosphere. Ideally you would be able to switch your antennas between vertical, horizontal, right hand circularly polarized, and left hand circularly polarized. The relays and cabling to do that are probably complex. Unswitchable circularly polarized (stuck in RHCP) antennas are a compromise though. With a circularly polarized antenna it seems you can get away with only a 3dB loss with no switching. Thanks Jean for the info. - John Brier KG4AKV

From: Jean Marc Momple <moc.liamg|elpmom.cram.naej#moc.liamg|elpmom.cram.naej>
Date: Sat, 15 Dec 2018 19:44:30 +0400
To: Bob Hammond <moc.liamg|rednirgporp#moc.liamg|rednirgporp>
Cc: AMSAT <gro.tasma|bb-tasma#gro.tasma|bb-tasma>
Subject: Re: [amsat-bb] Antenna separation on crossboom


So that all may fully understand:

Most LEO’s use monopoles or dipoles (on VHF/UHF) which are actually linear and not circular polarization, but the birds are spinning and tumbling therefore the polarization can be H, V or any angle. If you use H or V pole at the ground station the fading may be as high at 30dB therefore it is recommended to use circular polarization at the ground station as maximum fade would be around 3 dB whatever the satellite polarization may be.

I suggest that you use RHCP without polarisation switch, except if you wish to spend some money to experiment with same. I have the possibility to switch polarization but it is not used at all.

Hope this help.


Jean Marc (3B8DU)

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