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Re: Dish Antennas for S Band



Ed,
Tell me about your CP feed, I am waiting for my downverter to arrive in the
mail.
I have a dish to replace the BBQ grill it comes with.
Frank KL7FH in Alaska
----- Original Message -----
From: "Edward R. Cole" <al7eb@ptialaska.net>
To: <amsat-bb@AMSAT.Org>
Sent: Thursday, August 16, 2001 9:25 PM
Subject: Re: [amsat-bb] Dish Antennas for S Band


> >From: "Duffin, Jon" <jduffin@dbxpro.com>
> >I am currently using a 30 turn helix (theoretically 17dBic gain) for S
band
> >reception for AO-40 with moderate success.  I am thinking about taking
the
> >next step and possibly going with some sort of dish solution.  So, my
> >question is:  what is the thereotical gain for the following dishes at
> >2401MHz?
> >
> >18" DSS style dish
> >24" DSS style dish
> >Primestar dish (don't know the exact size -- but I guessing it would be
24"
> >x 36" oval shaped)
> >Myers BBQ style dish
> >
> >I would probably construct a circular style feed for these and use my DEM
> >preamp and 2880 converter.
> >
> >Comments?
>
> Jon,
>
> I ran my spreadsheet to give you gain figures for the above antennas.  I
> assume an efficiency of 55% for all:
>
> 1.  DSS 18-inch = 19.7 dBi
> 2.  DSS 24-inch = 22.2 dBi
> 3.  Primestar [36x24] = somewhere from 22.2 to 25.7 dBi {I would use 24.8}
> 4.  Meyers [32x34, I think] = 24.9 dBi
>
> Now realise that you lose 3 dB of your effective gain if you have a linear
> feed vs circular polarity feed.  Also, the offset feed dishes [DSS &
> Primestar will likely have ~ 0.5 dB more gain due to better efficiency;
the
> feeds do not block the dish].  I use a 33-inch offset feed dish [like a
> DSS] with a theoretical gain of 25.5 dBic [I use a 5-turn helix feed].
>
> From my own experience and reading of others experience, you will have
> better results on the S2-xponder with the last two dishes [in my opinnion
> one should shoot for at least 24 dBi gain].  I originally planned to use
an
> 18-inch DSS dish but moved up to the 33-inch and very happy I did.
>
> Ed
>
> ----
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