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Re: Helix phase center



Good Morning John,

I certainly can't claim to be definitive but I'm using a 47cm offset DSS
dish fed with a 5 turn helix.  I put the first turn of the helix at the
dish's focus.  Or put another way, the focus is 1 inch in front of the
reflector's feed.  If I ever get a stable signal source I want to try moving
it around to see if I can peak it up a bit more.

Lee-KU4OS

----- Original Message -----
From: "John Wright" <g4dmf@AMSAT.Org>
To: <amsat-bb@AMSAT.Org>
Sent: Friday, May 18, 2001 4:57 AM
Subject: [amsat-bb] Helix phase center


> Is there any definitive definition of where the phase center of helix
> should lie? I am currently trying to setup a 60cm offset dish for Mode S,
I
> have made a 3.5 turn helix, that has about the right beam-width to feed
the
> dish, but would like to have a rough idea as to where the helix should be
> in relation to where the Ku band LNB was. I think that the phase center
for
> the LNB is probably inside the mouth of the horn, the feed point is
> probably within the area covered by the original mounting clamp, so its a
> bit difficult deciding where to put the helix. I've tried to find data on
> Ku band LNB's to see if I can find where the phase center is on them, but
> have been unsuccessful. Perhaps it's not really that critical? Any help
> appreciated.
> John
>
> ____________________________
>
>       G4DMF  QTHR   IO93HA
>       Amsat-UK Member 5372
>           g4dmf@amsat.org
>       http://www.g4dmf.co.uk
> ____________________________
>
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