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Antenna noise temp

Now that I've gotten my primestar based AO-40 recieve setup on the air 
I'm trying to tweak it a little.  Currently I have a 5.25 turn helix 
mounted on a oval primestar dish feeding a 1.7db nf California Amplifier 
based downconverter.  According to W0LMD (ultimatecharger.com), the gain 
of the dish is about 27db (this seems a little optimistic).  Signals 
seem okay to me (I've never heard AO-40 on any thing but my own 
equipment) but SSB voice seems more difficult to copy than in recordings 
I heard.  The noise figure of my downconverter is a little higher than 
most so I was thinking a 2.4Ghz preamp might help things along a 
little.  Firstly though, my antenna is located in a high noise 
environment, downtown Houston, and my feed currently points towards the 
ground due to the offset feed angle.  This combined with 
over-illumination resulting from the oval shape of the dish leads me to 
believe that I have a relatively high antenna noise temperature.  I can 
hear 2.4Ghz spread spectrum cordless phones very well.  It is my 
understanding that a preamp won't help me as much in this situation 
because the noise will be amplified along with my signal.  What steps 
could I take to reduce the noise temperature of my dish?  Also what is 
the easiest way to measure my current S/N ratio and if possible my 
antenna noise temp?

David Carr

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