[amsat-bb] Re: RH and LH CP simutaniously

[Edward Cole]

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? Â  I admit my antenna theory is very weak 
> and surely someone would have considered this 
> long ago. Â  Thanks, RoD KD0XX --- On Fri, 
> 1/2/09, Nigel Gunn G8IFF/W8IFF 
> <nigel at ngunn.net> wrote: From: Nigel Gunn 
> G8IFF/W8IFF <nigel at ngunn.net> Subject: Re: 
> [amsat-bb] RH and LH CP simutaniously To: "R. 
> Chastain" <suenrod at yahoo.com> Cc: "Amsat-BB" 
> <amsat-bb at 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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> Nigel A. Gunn. G8IFF   W8IFF (was KC8NHF) 1865 
> El Camino Drive, Xenia, OH 45385-1115, 
> USA   937 825 5032 e-mail 
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> http://www.ngunn.net Member of  ARRL, GQRP 
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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