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Re: Circular Polarity




I have another question for the experts in the group.  Commercial
Satellite feeds for CP (this is my understanding) often are linear probes in 
a horn and a (either 1/2 wl or a 1/4 wl-- i don't know) dielectric lens is 
placed at a 45 degree angle from the probe.. I guess the lens is machined so 
the signal is "slowed down" more in one section than the other and the 
signal becomes CP..

Does anyone know of some references for how this works?  Also on 10 GHz is 
it possible to scrounge one of these devices (or the whole feed) from a DSS 
LNB?

Fred W0FMS


>From: "Edward R. Cole" <al7eb@ptialaska.net>
>To: James Sharp <jsharp@psychoses.org>
>CC: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] Circular Polarity
>Date: Fri, 29 Dec 2000 22:04:15 -0900
>
>James,
>
>This [helix antenna designs] was a topic on this list about two weeks ago.
>Hopefully someone who kept the info will respond.
>
>As far as 10 GHz goes, I would discourage you from making a helix.  A
>better antenna would be a small dish fed by a horn.  Instead of circular
>polarization, I would make a circular horn [3/4 inch dia] with two coax
>probes at 90 degrees and chose which ever one [polarization] that gives the
>strongest signal.  A 60cm dish will produce a signal 20 dB over noise if
>your preamp has a noise figure of 1.5 dB.  An 18 inch DBS offset feed dish
>is only 3 dB less gain and can be gotten from mcm electronics for around
>$30.  That's what I plan to use [well, I also have a 2.5m dish for 10 GHz
>with a .79 dBNF preamp].
>
>Ed
>
>At 11:48 PM 12/29/00 -0500, you wrote:
> >
> >Anyone have or know of a program to help design helical antennas?
> >
> >I'd like to build one for the 1.6 Ghz GEOS satellites, plus a 2.4 Ghz and
> >maybe 10ghz for Oscar work.
> >
> >
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> >
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