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Re: Re: no patches for offset dishes!!



Oh, I know they're not earth shaking, Cliff, and they have been
mentioned before.  I'm just wondering what the trade-off is.

>From what I have been able to gather:

1) the helix is nice because based on the number of turns you can
control the beamwidth, and match the pattern of the feed to the dish at
hand....  the higher the f/d, the more turns. The down side is, I run
portable, and unless the helix is encased or protected, it gets banged
and bent.

2) the patch has a fixed beamwidth which matches well to a center fed,
low f/d (0.3) dish. I want to use it on a high f/d (0.6-0.7) offset
dish. In that case, I will be over illuminating the dish, and picking up
noise.

3) if I add a scalar ring, like the aperture of a camera lens, I can
close down the illumination. So the question is:

What is the down side of doing that?

I was going to eye ball it...  that is, I'm going to size the ring so
the left edge of the patch can just see past the ring to the right edge
of the dish. Valid?

Bill
W1PA
----- Original Message -----
From: <cbuttsch@slonet.org>
To: "Bill Acito" <w1pa@hotmail.com>
Cc: <amsat-bb@AMSAT.Org>
Sent: Friday, July 12, 2002 12:18 PM
Subject: [amsat-bb] Re: no patches for offset dishes!!


> Hi Bill and all.  This little contribution is so far from earth
shaking
> I had to wait until someone mentioned the construction of a shroud for
> either a helix or patch.  For years many of us have used HUNT's whole
> tomato cans as raw material as they are four inches in diameter
without
> ridges---that is straight sides just as a shroud should be!  Seems
now,
> HUNT's has reverted to ridges on all products.  You might consider
> checking grocery shelves for remaining smooth cans while you are able.
> Told ya it was not earth shattering!!  Cliff K7RR

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