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Re: Mode S feed for TVRO Dish



Just a word of precaution, you can get quite substantial attenuation just
below the cut off frequency of a wave guide. I would recomend measuring the
dimensions of the feed. For linear polarisation you need at least 1/2
wavelength (free space) across the longest dimension (the magnetic field
direction) and for circular polarisation you usually need a round waveguide
of 1/2 wavelength (free space) minimum dimension.

Regards,
Murray Peterson
VK2KGM
----- Original Message -----
From: "Howie DeFelice" <hdefelice@petrexintl.com>
To: "John Brown" <n4cnn@yahoo.com>; <amsat-bb@AMSAT.Org>
Sent: Wednesday, January 31, 2001 4:07 AM
Subject: Re: [amsat-bb] Mode S feed for TVRO Dish


> My guess would be that the existing TVRO feed may work OK. The spec for
> WR-229 shows low end cut-off at 2.577 GHz. You would need a waveguide to
"N"
> transition to connect the downconverter. You might be able to fabricate
one
> from the old LNB. Otherwise, the 3 turn helix feed described by G3RUH
should
> work pretty well. Typical F/D of that type antenna is around .37
>
> Howie
> AB2S
>
> ----- Original Message -----
> From: "John Brown" <n4cnn@yahoo.com>
> To: <amsat-bb@AMSAT.Org>
> Sent: Monday, January 29, 2001 7:22 PM
> Subject: [amsat-bb] Mode S feed for TVRO Dish
>
>
> > I have a 10' TVRO dish with weeds growing around it
> > out in the back yard.  Anyone have any suggestions on
> > a feed to use for Mode S?  Have a Drake on the way and
> > figure I would get the weed eater out and get started
> > on a new project.
> >
> > John - N4CNN
> >
> > __________________________________________________
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