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Re: 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
>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.


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.


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