Re: [amsat-bb] Info Needed

["Frederick M. Spinner" <fspinner@xxxxxxxxxxx>]

Although many have reported success with a patch feed and a offset fed dish, 
the effective 0.7 f/d of the offset fed dish is not theoretically suitable 
for a patch feed.  Patch feed's gain/beamwidth are suitable for a 0.3-0.4 
f/d.

The 5 turn helix, with a cavity back, seems to be the most suitable feed 
devised for such a dish so far.

Fred W0FMS


>From: "Edward R. Cole" <al7eb@ptialaska.net>
>To: <amsat-bb@AMSAT.Org>
>Subject: Re: [amsat-bb] Info Needed
>Date: Wed, 28 Nov 2001 09:49:12 -0900
>
> >From: "Jack O'Mara" <jomara@erols.com>
> >Hi Folks
> >
> >I just picked up a 1.2 meter offset fed dish made by Channel Master.
> >I would like to compare it to my 4 foot andrews dish . What I'm
> >looking for is has anyone designed a helical feed for this dish?
> >If so could someone point me to the web page or where ever that
> >contains this info. This will be used for the downlink of AO-40
> >on S band.
>
>Jack,
>
>Not sure if you received an answer, but my understanding on all Ku-band
>direct satellite dishes is that they use the same feed/LNB's so the dish
>curvature is the same regardless of size.
>
>Tha being so a feed for any offset KU-band TVRO dish will be universally
>usable.  The feed needs to have a beamwidth suitable for a dish of F/d =
>0.7.  A 5-turn helix is suitable and the patch antenas discussed on the bb
>should be also.
>
>Maybe others will publish a web site shoing these.
>
>Ed
>
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