[amsat-bb] Re: Polarity questions
kl7uw at acsalaska.net
Sat Sep 20 11:18:18 PDT 2008
At 03:56 AM 9/20/2008, Anthony Monteiro wrote:
>At 07:29 PM 9/19/2008, Clint Bradford wrote:
> > >>...I have to disagree with Clint...
> >I just must be the luckiest S.O.B.(*) working AO-51, then...During
> >demonstrations in front of folks, someone in the assemblage almost
> >always asks about polarization. I twist the Arrow, and we all "hear"
> >no difference in its strong, clean signal.
> >Clint, K6LCS
>Dear Clint and friends,
>There is no luck involved. The UHF downlinks on AO-51 are
>circularly polarized. You can twist your Arrow all you want
>and you will not hear any difference, nor could you measure
>any because there isn't any difference!
>The cross-polarization loss from a circular TX antenna to a
>linear RX antenna is a constant 3 dB regardless of the
>actual linear polarization angle.
>If you want to demonstrate polarization mismatch loss, use AO-27
>(which is linear) with an Arrow.
Well, theoretically the signal from AO-51 might be somewhat
elliptical if there is a significant squint angle. Apparently this
does not happen with enough change to be detectable. The human ear
cannot detect audio level differences under 3-dB. Other effects
probably mask any measurable variance.
73 Ed - KL7UW
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