----- Original Message -----
From: "Edward R. Cole" <kl...@acsalaska.net>
To: "Paul Delaney - K6HR" <paul.hamra...@verizon.net>; <amsat-bb@amsat.org>
Sent: Monday, March 14, 2011 7:54 AM
Subject: [amsat-bb] Re: Using Preamps In Shack
> Recently I lost one of my eme preamps on my tower and used a preamp
> at the shack. My normal system NF = 0.76 dB. In the shack I had
> 0.25 + 1.7 dB cable loss = 1.95 dB NF. That lowered my sensitivity
> by about 5 dB but I still received eme signals.
>
> 73, Ed - KL7UW
>
Hi Ed, KL7UW
When you write that your sensitivity lowered by about 5 dB you are
absolutely correct and infact I played with numbars to verify your
statement.
Your normal system NF = 0.76 dB
Your normal system noise factor F = 10E (0.76/10) = 1.19
Your normal sys. noise temp. T = ( F-1) x 290 = 0.19 x 290 = 55 kelvin
In the shack system NF = 1.95 dB
In the shack system noise factor F = 10E (1.95/10) = 1.56
In the shack sys noise temp. T = ( F-1) x 290 = 0.56 x 290 = 164 kelvin
Your actual reduction in S/N ratio = 10 log (55 / 164 ) = - 4.74 dB
10
You can check your actual S/N reduction of 4.74 dB receiving Sun Noise
or your own Moon echoes.
By the way a reduction of about 5 dB receiving EME signals is a big S/N
deterioration and so put again the preamplifier at the antenna is mandatory.
When I was on 432 MHz EME early 1977 to 1980 my array was 16 x 21
element yagi and using an antenna mounted home brewed preamplifier
with a GaAsFET V-244 the Sun Noise was about 15 dB at that epoch time
and it was possible for me to receive my own CW echoes from the Moon
Using a more noisy home brewed preamplifier with a bipolar transistor
FJ-203F from Fujitsu antenna mounted the Sun Noise was about 10 dB but
it was absolutely impossible to receive my own echoes from the moon even
using my 1 kW K2RIW power amplifier.
Nice to remember but unfortunately a big storm destroyed my array at the
end of 1980 !
In a separate email I have sent a picture of it.
Best 73" de
i8CVS Domenico
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