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R: Helix phase center




Hi  Lee,

I  founded the phase center of the elix at the same distance of  25 mm  (or
one inch ) from the elix reflector
My dish is  1,2 meter prime focus with 0,45 F/D and  3 turns elix LHCP feed
is needed to illuminate the edge at -10 dB approximately and get RHCP by
reflection from the dish.
For your 47 cm offset dish 5 turns  for 2400 MHz is correct by our
experiments in Italy

73 de i8CVS Domenico

----- Original Message -----
From: Lee <lee-fl@cfl.rr.com>
To: <amsat-bb@AMSAT.Org>
Sent: Saturday, May 19, 2001 1:51 PM
Subject: Re: [amsat-bb] 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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>
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