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Re: Up and dwnlink polarization of HAMSAT



Thanks Drew.
Your comments are appreciated.

I thought I had read somewhere that a radio receiver senses a CP wave
as the opposite CP polarization from the transmitters view.

I am glad we have the expertise of others, sharing their experiences
through this medium, to keep us straight.

73,
Charlie, N5TD


----- Original Message ----- 
From: "Andrew Glasbrenner" <glasbrenner@mindspring.com>
To: "Charlie Schlieper" <n5td@vvm.com>; "Don,w7das" <w7das@cox.net>; 
<amsat-bb@AMSAT.ORG>
Sent: Friday, July 01, 2005 2:05 PM
Subject: Re: [amsat-bb] Up and dwnlink polarization of HAMSAT


> No...RHCP matches RHCP. Think of it this way. Take two bolts, both with 
> the same threads. Think of them like helixes. Put a nut on one bolt. Point 
> them at each other like antennas would be. Move them close enough together 
> that the ends touch. Notice how the nut (the wavefront) will thread off 
> the first bolt right onto the second! If a LHCP transmit antenna required 
> a RHCP receive antenna this would not be true.
>
> It's a simplistic analog, but always one that helped me understand 
> circularity.
>
> The part about defining what constitutes RH or LH is true though. Groups 
> disagree on which way the thumb points for which one, LOL. Been too long 
> for me to remember who's on what side of that fence.
>
> 73, Drew KO4MA
>
> -----Original Message-----
> From: Charlie Schlieper <n5td@vvm.com>
> Sent: Jul 1, 2005 2:29 PM
> To: "Don, w7das" <w7das@cox.net>, amsat-bb@AMSAT.ORG
> Subject: Re: [amsat-bb] Up and dwnlink polarization of HAMSAT
>
> By golly, I think you're right Don.
>
> You just reminded me not only of that, but the fact that Optical theory
> denotes the polarization (polarisation) opposite from us radio guys, or
> as the twist is seen coming into the RECEIVE antenna, instead of the
> TRANSMIT antenna relationship.
>
> Thanks for that refresher!
>
> Charlie, N5TD
>
> ----- Original Message ----- 
> From: "Don, w7das" <w7das@cox.net>
> To: <amsat-bb@amsat.org>
> Sent: Friday, July 01, 2005 9:18 AM
> Subject: Re: [amsat-bb] Up and dwnlink polarization of HAMSAT
>
>
>>I may have read incorrectly, but I thought polarisation was determined by
>>the rotation of the electric field about the axis as the wave moved AWAY
>>from the source.  If this is true, wouldn't the polarisation be opposite 
>>as
>>it arrived on Earth?  i.e. transmitting with an LHCP antenna in space 
>>would
>>be best received with an RHCP antenna on Earth?
>>
>> 73,
>> Don
>>
>>
>> ----- Original Message ----- 
>> From: "William Leijenaar" <pe1rah@yahoo.com>
>> To: <amsat-bb@amsat.org>
>> Sent: Friday, July 01, 2005 2:37 AM
>> Subject: [amsat-bb] Up and dwnlink polarization of HAMSAT
>>
>>
>>> Hi AMSATs,
>>>
>>> This morning I received the answer from ISRO about my
>>> question for the uplink polarization, and why they
>>> used LHCP on the downlink.
>>>
>>> The uplink of HAMSAT is in RHCP, opposite of the 2m
>>> downlink that is in LHCP.
>>>
>>> I was also supprized to hear that the downlink is in
>>> LHCP, as most amateur sats use RHCP.
>>> The reason that ISRO used RHCP and LHCP is to avoid
>>> interaction between the uplink and downlink signals.
>>>
>>> By using opposite polarizations the output of the
>>> satellite would less interact on its 70cm input.
>>> Personaly I think the antennas are at such close range
>>> that this will not really help...
>>> At least we know the right polarizations, and the
>>> reason why it is done.
>>>
>>> Myself I have fixed RHCP antennas, and actually have
>>> had never any problems with the HAMSAT.
>>>
>>> On the other hand the signals are that strong that it
>>> should be no problem, and most of the hams I hear on
>>> HAMSAT are in aligator mode and can use some
>>> polarization attenuation on the uplink :o)
>>>
>>> 73
>>> William
>>> PE1RAH
>>> ---
>>> ----
>>> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
>>> Not an AMSAT member? Join now to support the amateur satellite program!
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>> ----
>> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
>> Not an AMSAT member? Join now to support the amateur satellite program!
>> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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