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Father Bill's offset dish



Father Bill,
Welcome to AO-40. I did been away from the satellite hobby for 25+ years and
just got back into it last fall. Wow! What a wonderful learning experience.
I have had more fun with AO-40 then I could imagine. This -bb is also
wonderful. The ability to get fast answers from people who know is great.
In general, it is best to have the D/C as close to the feed as possible.
There are some practical issues including that it serves no good to put  it
so close that is obscures part of the area of the dish that would otherwise
provide additional signal. When you look at mine you will see that I have
about 6-10 inches of coax from the feed to the D/C.
I am not familiar with your D/C but with my UEK-3000 it is generally
excepted that a preamp in front of the D/C is a bad thing. While it will
apply gain to the signal it will also provide gain to the noise and
introduce it's own additional noise. Other operators have convinced me that
the feed should go directly to the D/C without any additional preamp. You
should experiment with this issue and draw your own conclusions. Remember it
is not the S meter reading that counts, it is the signal to noise ratio that
matters. That is the only thing that can give you arm chair quality. In
general, if you don't like the S/N ratio you have, you need a bigger dish to
capture more signal. This assumes you have a good D/C. There is a wonderful
URL that gives you an overall system analysis for S/N ratio. Plug in your
numbers and check it out. You can also check out my suggestions regarding
preamps. It is listed below.

Regarding you Patch feed. Mounting properly is critical. You want the focal
point of the Patch, which is about 1/8" from the rear reflector (between the
rear reflector and the front hot plate) to be at the dish focal point. The
info on my web site is only relevant to the 1.2m offset dish I am using. You
will need to get the specifics for your dish. If your dish has a factory
feed mounted, you can use those dimensions. Just remember that an offset
dish takes a bit more thinking since that offset angle must be maintained.

I hope this gives you some helpful info.

Good luck on you station construction and we'll see you on AO-40.


URLs of interest:

W8GSM rig: www.wmfd.com/w8gsm
System noise/power budget calculator: This is an attachment on the direct
e-mail only.
A great site on AO-40 (W0LMD): www.ultimatecharger.com/dish.html


Gunther Meisse
W8GSM
AMSAT LM: 594


-----Original Message-----
From: Bill Jablonske [mailto:bill@jablonski.com]
Sent: Friday, November 16, 2001 3:10 AM
To: Gunther Meisse
Subject: ChannelMaster offset etc



Gunther

I have seen your postings frequently and have something similar here.  Can I
ask for a few details and information?

I have a Primestar ChannelMaster offset dish complete with arm and D/C. I
have a Cal-Amp D/C I am in the process of converting; I plan to order
(G3RUH?)the new Patch commercial offering from England. Last I will get a
Kuhne pre-amp and should be ready to go.  I do have a 50' crank-up with M2
boom, M2 2M and 440 and want to put this on there also.

The add this to the equation:  I have NEVER worked the satellites before
even though I have been a life member (LM490).

I finally have retired a little. and have my own home now and can put up a
tower. So here we go; age 67 and brave or foolish.  This is a steep learning
curve but fun anyway.

What distance should the the D/C be from the dish surface?  I do not know
exactly where the 'feed' is on the attached D/C , how deep or from what
point I should measure.  And then should I keep it all inline or just put
the patch in place and cable connect to the D/C and Pre-amp attached to the
outside surface of the arm? Or should the D/C remain in the house near the
847?

Do you have a web site?  Pictures?


Any advice or direction is very welcome.  Thanks.

(Father) Bill Jablonske  W9NNS
w9nns@amsat.org
bill@jablonski.com
EN45im
715-865-6154 collect

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