[amsat-bb] Re: Antenna Polarization Technical Question

[Thomas Doyle]

Thanks to Domenico for sharing the work done by K4KJ. It is amazing
how much good information there is out there. It takes a bit of
digging to find it but it is worth the effort. The configuration shown
in figure 14 looks promising but probably too difficult to put on a
sat.

W9KE Tom Doyle

On Sat, Aug 4, 2012 at 10:18 PM, i8cvs <domenico.i8cvs at tin.it> wrote:
> Hi All,
>
> I agree completely with Bob, WB4APR and this is what is wery well
> explained into the article "CIRCULAR POLARIZATION by K4KJ,
> a zipped file 5 MB long available from me.
>
> 73" de
>
> i8CVS Domenico
>
> ----- Original Message -----
> From: "Bob Bruninga " <bruninga at usna.edu>
> To: "Thomas Doyle" <tomdoyle1948 at gmail.com>
> Cc: <amsat-bb at amsat.org>; "andrew abken" <kn6za at hotmail.com>
> Sent: Sunday, August 05, 2012 12:24 AM
> Subject: [amsat-bb] Re: Antenna Polarization Technical Question
>
>
>> > Not sure why anyone would want to maintain the
>> > orientation of the satellite in such a way that
>> > would cause the direction of circular
>> > polarization to change during the path.
>>
>> Lets try this approach... As I said before,  By the laws of physics, what
> comes out one side of a circular polarized low gain antenna as RHCP comes
> out the opposite side as LHCP.
>>
>> Now given that, and the fact that someone in Maryland is in the center of
> the RHCP beam, then by the laws of physics, the guy in California must see
> mostly LHCP.  No matter how much one of those persons demands that he
> deserves the RHCP beam, by definition, someone else somewhere will get the
> LHCP one, and the geometry changes at least every 10 minutes or so and every
> time the spacecraft rotates a bit.
>>
>> So one might say, "point it down" then only the person in Kansas will see
> the main beam and those in CA or MD will be completely off the sides almost
> 70 degrees from the main beam.  Mot people do not realize how LOW these
> satellites are.  The only solution is to put satellites so high, that "down"
> is about the same to everyone (geostationary altitude).  But then that takes
> 100 times more altitude, and that takes 10,000 times more power.
>>
>> Better to just live with the laws of physics... I guess.
>>
>> Bob, WB4aPR
>>
>> >
>> >On Sat, Aug 4, 2012 at 2:47 PM, Bob Bruninga <bruninga at usna.edu> wrote:
>> >>> I believe that is true but that does not explain
>> >>> why the optimum polarity setting on the receive
>> >>> end would change during a pass.
>> >>
>> >> That's easy.  The circularity on a pair of crossed dipoles (about all
> you can get on a spacecraft) May be designed for Right hand circularity when
> viewed from the prime direction.  But by definition, that save waveform will
> be LHC when viewed from the opposite direction.
>> >>
>> >> And since the geometry to any one observer is constantly changing by
> almost 180 degrees during an overhead pass, that is why it is very easy to
> see, complete change in circularity.
>> >>
>> >> Bob, WB4APR
>> >>
>> >
>> >
>> >
>> >--
>> >
>> >Sent from my computer.
>> >
>> >tom ...
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>



-- 

Sent from my computer.

tom ...