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Re: Polarity questions



....I agree with Gus. And the difference is 20-30 dB depending upon the
construction, reflections,
lobes of antennas and other complex parameters.

 In general a Cross-Yagi which appears a very good circularity, then rising
easily to 30 dB
between RHCP-LHCP.

 Tim,
 also keep in mind, by using CP the fading is much less and never the signal
has
too much "deep" .
Having in mind that the LEOs changing quite often the polarization, I
believe the
switching between RHCP-LHCP is mandatory,  if always you looking for good
RX-TX conditions .  A mere example was the last pass of AO-7 over my QTH .
During the ascending orbit it was 5 S-units without preamp and almost close
to TCA the signal
dropped down to Zero (Q5). By changing my antenna to the opposite
polarization,
it was again 5 S-units. That is a great difference on receiving.

  So, If you want just to play with LEOs and you are not looking for the
optimum,
you can do it by using stable polarization. However it's compromise
and manytimes you will wonder why the satellite is too weak and some other
times "booming".


73, Mak SV1BSX




----- Original Message ----- 
From: "Angus" <angus@young5769.freeserve.co.uk>
To: <AMSAT-BB@amsat.org>
Sent: Friday, September 19, 2008 5:29 PM
Subject: [amsat-bb] Re: Polarity questions


> if the satellite is running RHCP and you have LHCP the VHF/UHF Manual
> handbook says 20 -30dB which is a lot!
> having spent ages getting a homebrew polarity control box to work just
> right, I can honestly say it was well worth the effort!
> regards
> Gus M0IKB
> ----- Original Message ----- 
> From: "Tim Tapio" <tim@timtapio.com>
> To: <amsat-bb@amsat.org>
> Sent: Friday, September 19, 2008 1:58 PM
> Subject: [amsat-bb] Polarity questions
>
>
>>
>> Hi,
>>
>> How much signal reduction is there as the result of having the wrong
>> circular polarization?
>> I'm looking at M2 circular antennas for the 70cm downlink, it's another
>> $200
>> for the switching to change polarity (woo hoo).
>>
>> 73 de Tim, K4SHF
>>
>>
>>
>>
>> _______________________________________________
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>
>
> _______________________________________________
> Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author.
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