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Re: Re: no patches for offset dishes!!



Hi the downside is there is a practical limit to how much you can "choke" 
out with a scalar ring.

My knowledge isn't good enough yet to tell you what that limit is.
Making a shroud that is adjustable, you can tune for max smoke.  (Ok, max 
beacon s/n...)

But, go as far as you can and you'll be over-illuinating the dish less.  And 
that is still an improvement.

Good Luck,

Fred W0FMS


>From: "Bill Acito" <w1pa@hotmail.com>
>To: <cbuttsch@slonet.org>
>CC: <amsat-bb@amsat.org>
>Subject: Re: [amsat-bb] Re: no patches for offset dishes!!
>Date: Fri, 12 Jul 2002 13:33:53 -0400
>
>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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