Re: [amsat-bb] Cupping a patch feed

["Lee" <lee-fl@xxxxxxxxxx>]

Bill,

I've tried both with my 60cm Sony DSS dish.  In my case I need a feed with a
90 degree beamwidth.

For the helix I've used 5 turns.  This gives me the desired beamwidth and I
believe that the circularity is better than helix feeds with only 3 turns.
I have also tried the K3TZ patch with good results. Putting in into a deep
cup seemed to lower the noise floor maybe 3 dB.  The most notable thing for
me was that it seemed to pick up less of the neighbor's cordless phones from
the side.  In my case I made the sides of the cavity equal to the radius of
the reflector.

My suggestion is try both, experiment some and let everyone know what worked
best for you.


Good Luck,
Lee-KU4OS

----- Original Message -----
From: "Bill Acito" <w1pa@hotmail.com>
To: <amsat-bb@AMSAT.Org>
Sent: Wednesday, October 23, 2002 12:52 PM
Subject: [amsat-bb] Cupping a patch feed


> Assuming an offset fed dish (sometime I wished I lived in Europe, where
> the small f/d dishes are so prevalent...):
>
> f/d is +/- .6
> therefore, illumination angle about 70 deg.
> Matched helix feed gives proper illumination, but some side lobes and
> the axial ratio is not as good (per my reading).
> A patch over-illuminates (+/- 130 deg), but better axial ratio (less
> QSB) and no side lobes.
>
> Not knowing all the physics and the math of the pattern, if I cup the
> patch enough so it only "sees" the offset dish (effectively cutting off
> part of the "volume" of the patch's pattern), will I effectively reduce
> the gain of the patch?...
>
> In other words, some practical experiences describe a patch on an offset
> dish having the same relative signal strength for signals vs a helix,
> less QSB, but more background noise. If I cup the patch, can I reduce
> the noise component, and keep the same QSO signal strength, when I have
> effectively cut off the outer ring of the pattern?
>
> Bill
> W1PA
>
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