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Re: C Band AWSOME !



>  I don't have a circular polarized
>antenna at the moment. I am going to build a two pound coffee can >feed 
>when
>time permits. YES, I KNOW it doesn't weigh two pounds, and yes I know >it 
>is
>not circular polarization.  If anyone has a  three to five turn helix >they
>want to get rid of, please let me know.
>

As far as a coffee can goes, there are two ways I can think of to
make it circular:  #1 is to use a piece of dielectric, like teflon, or
maybe even plexiglass or polycarbonate placed at a 45 degree angle
fron the probe (one direction is LHCP, other is RHCP, try it both ways).  
The other is to build two probes at a 90 degree angle and feed it 90 (or a 
multiple of 90) degrees out of phase.  It'd be interesting
to see a design for that be synthesized.

As far as the helix:  You can build one in a hour or so.  Insulated #12 AWG 
on thinwall 1" PVC is close to the correct diameter for the
helix at 2401 MHz.  I'd advise around three turns for the f/d of a
typical TVRO dish.  You can play with the pitch angle by spreading
and compressing the turns of the helix for best pattern.  At some
point you can try to play around with the match, but I've found
that for RX with a dish, that a good match is nice, but not an
absolutely necessity.

By the way, before I moved to Iowa, and picked up a "no TVRO dish"
covenant, I used my TVRO dish with a 1691 MHz "tapewound" helix 
(intentionally taking the 3dB hit from the GOES linear polarized sats-- 
didn't have to worry about rotating the feed this way!) slightly offset from 
the main feed, and used to get full "P5" no noise
WEFAX pictures.  So yeah, I'm not suprized it works well for AO-40

Fred W0FMS

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