At 06:27 PM 1/3/2009, R. Chastain wrote:
From what I have read from people with switchable RHCP/LHCP, they can switch to the other polorazation to combat fading. Wouldn't doing this at a fast rate accomplish the same goal?  I admit my antenna theory is very weak and surely someone would have considered this long ago.  Thanks, RoD KD0XX --- On Fri, 1/2/09, Nigel Gunn G8IFF/W8IFF nigel@ngunn.net wrote: From: Nigel Gunn G8IFF/W8IFF nigel@ngunn.net Subject: Re: [amsat-bb] RH and LH CP simutaniously To: "R. Chastain" suenrod@yahoo.com Cc: "Amsat-BB" amsat-bb@amsat.org Date: Friday, January 2, 2009, 6:28 PM Would effectively cause a 3dB loss of antenna gain as seen by another circularly polarised antenna as the receiving end would receive negligable signal 50% of the time. R. Chastain wrote: > Hi all, > ��� Has anyone ever considered the possibilty of using PIN diodes and a free running square wave oscillator to electronically switch between RHCP and LHCP? > The switching frequency would have to be high enough so as to not introduce > a tone to the signal. > � > Just a thought I have had for awhile. > � > RoD > KD0XX > > > _______________________________________________
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The problem with switching is knowing when to switch. If you switch to LHCP when the signal favors RHCP you will not hear anything due to 20-dB cross polarization loss. The change of polarization isn't a regular event (or predictable for the average ham). Another approach to polarization diversity would be by using two receivers. One connected to RHCP and the other to LHCP, The receivers would need to be in phase sync (use a common LO). Then using a program like Winrad (or Linrad if you use Linux) the actual polarization will display and be maximized. You can feed each receiver to a stereo headphone and you will hear the shift go from side to side. Such a system is used on eme by a few folks. It is a bit more complicated to do than switching, as you propose.
A better approach for satellite is just having the capability to switch pol when it is needed. if signals begin to fade, you switch pol to check if that is better.
73, Ed - KL7UW