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AO-40 spreadsheet



Wow, this spreadsheet is truly enlightening.  There's nothing better
than a good model to quickly teach how things work.

I notice that the ability to hear the transponder is VERY dependent on
the antenna gain, and relatively independent on the gain of the preamp.
For example, there appears to be no benefit to having a preamp gain of
more than 10-15 db.  Same for the Converter.  Don't waste your money on
super high gain components, just get a really good antenna.

So, my question:  Given the high dependence on antenna gain, besides
renting Arecibo for the weekend, what will give the most gain for the
buck?  I'm starting with an 18"x36" grill antenna with a dipole+hat feed.

  Increasing the size of the grill to about 30" x 36"
  Replacing the feed with a 2 1/2 turn helix
  covering the grill with a metal screen
  eliminating the 3-odd feet of RG-8 coax between feed and preamp
    (i.e. mount the preamp at the feed)

I think the answer to this is "none of the above".  If I've got this
right, none of these really increases the gain of the antenna itself,
just makes it pick up more of the signal and noise around it.  The
big gain will come by getting an antenna that has a sharper pattern, 
which will pick up the same signal and less background noise.  Sure,
improving the reflector and feed helps, but putting the same feed on
a wider grill mostly increases S+N, not just S.

Basically, getting a good signal from a mediocre antenna is hard.
Making a really good antenna, of course is hard too.  Where's the
sweet spot?

Thanks for the help,

Greg.
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