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Re: S-band receiving requirements



In a message dated 5/18/01 8:40:08 PM Eastern Daylight Time, 
al7eb@ptialaska.net writes:

>  Gene Marcus' spreadsheet is very useful for this process.

I agree!!  A couple of pointers..... 

The very first coax loss number before the preamp is very important. This 
really effects overall system noise. I calculated the 3 foot jumper (RG-8) on 
my Meyers dish as -.36 dB at 2400 (yuk). Throw that number in the spreadsheet 
and see what happens.

Also, I asked Gene about the antenna gain. The number you input is dBi 
Linear. So to be accurate, if you're using a Meyers dish you should subtract 
3 dB for the theoretical loss when going from linear to circular. So, for a 
Meyers dish that was advertised as 25 dBi, you would input 22 dBi.

I can see if I were to do any improvements to my system, I'd probably attack 
the antenna. I already have a good low NF preamp. The changes I'd contemplate 
would be to change the feed to circular and reduce the coax loss before the 
preamp. To see the effect of these two changes, input .1 dB for first coax 
loss and 25 dBi antenna gain in the spreadsheet and you'll see the 
improvement.

Now back to cobbling together a 5668 uplink :-}

73,
Mike, N1JEZ
AMSAT #29649
Local Area Coordinator
"A closed mouth gathers no feet."
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