----- 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 _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb