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
But why should I have to check? That's one of the computers jobs.
Edward Cole wrote:
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.
Then as suggested, you have a receiver set for each case and let them vote as to has the best signal...that's letting the computer do the work....
Tim T. K4SHF
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Nigel Gunn G8IFF/W8IFF Sent: Sunday, January 04, 2009 8:19 AM To: Edward Cole Cc: amsat-bb@amsat.org Subject: [amsat-bb] Re: RH and LH CP simutaniously
But why should I have to check? That's one of the computers jobs.
Edward Cole wrote:
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.
_______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Tim,
Sort of like voting. Actually both receivers are receiving full time. The computer combines this information and the signals received to both display the effective polarization angle and produce a maximized signal output. An alternative that is available with Winrad and Linrad is to output each audio stream to the right and left ear of a stereo headset with the result your ears and brain process the effect. Polarization changes produce a stereo effect, as it were. This is currnently being done be eme stations!
HF stations have long done diversity reception by use of two recevers and antennas separated by some arbitrary amount. When done with FM repeaters the repeater compares all received signals and choses (votes) for the best signal to repeat. This is largely an analog system.
For eme and possibly satellite application audio is digitized and processing is done in the computer with audio reconverted from the system.
73 Ed - KL7UW
At 04:40 AM 1/4/2009, Tim Tapio wrote:
Then as suggested, you have a receiver set for each case and let them vote as to has the best signal...that's letting the computer do the work....
Tim T. K4SHF
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Nigel Gunn G8IFF/W8IFF Sent: Sunday, January 04, 2009 8:19 AM To: Edward Cole Cc: amsat-bb@amsat.org Subject: [amsat-bb] Re: RH and LH CP simutaniously
But why should I have to check? That's one of the computers jobs.
Edward Cole wrote:
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.
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
participants (3)
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Edward Cole -
Nigel Gunn G8IFF/W8IFF -
Tim Tapio