Domenico:
Greetings once again. You sent me a note some time ago that helped to amplify my current belief concerning SNR.
I am willing to bet two things.
First, it is difficult (not impossible, just difficult) to obtain a better front end noise figure than what the original receiver manufacturer has created. Almost certainly the addition of an outboard amp will add more noise. And this is not always a bad thing. A preamp can be a great addition despite the addition of more noise. But then you get into a curve of cost vs true value of gain. Is it worth it? Maybe so.
Second, it is very unlikely that maximum signal strength will be at the same point as maximum signal to noise ratio (SNR). Again, maybe this is not a bad thing in any one individual case. Almost certainly the best SNR will be at a point of gain somewhat less than maximum.
I work with receivers and preamps that cost dozens of thousands of dollars. Cost and receive noise figure is almost a logarithmic curve. And it seems that only with the very best front ends are SNR and gain at the same point.
Once you get the best receiver, coax and antenna you can afford, that is all you can do....which seems like a dumb and obvious thing to say. Beyond that, true magic is hard to come by. And I am not knocking the preamp. Again, I own and use them all the time.
73!
Gary, N7BRJ/DA1BRJ
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of i8cvs Sent: Tuesday, September 18, 2007 6:17 PM To: Gary Memory; 'Jim Jerzycke'; 'Bob Stewart'; 'Amsat-BB' Subject: [amsat-bb] Re: New Preamp
----- Original Message ----- From: "Gary Memory" gmemory@tks-net.com To: "'Jim Jerzycke'" kq6ea@pacbell.net; "'Bob Stewart'" bob@evoria.net; "'Amsat-BB'" amsat-bb@amsat.org Sent: Tuesday, September 18, 2007 8:22 AM Subject: [amsat-bb] Re: New Preamp
I have a WACCOM cavity filter for both VHF and UHF that I'd like to use at the mast head, but they are too big to get up there (and they are not weather proof). Oh, and they are only a couple dozen KHz wide, which
makes
tuning to a different frequency a bummer.
Gary, N7BRJ/DA1BRJ
Hi Gary, N7BRJ/DA1BRJ
For my similar situation in the bay of Naples wich is full of RF pollution I use the following K3PGP home brewed filter at the mast head in front to the low noise 70 cm preamplifier and a 70 cm cavity filter in the shack in front of my 70 cm downconverter or 70 cm receiver.
Please read the article.
http://www.k3pgp.org/432filter.htm
Similarly for 2 meters I have scaled the dimentions of the above filter wich is antenna mounted in front of the 2 meters preamplifier and a 2 meters cavity filter of the type used for the FM repeaters is in the shack in front of my 2 meters downconverter or receiver.
I remember receiving OSCAR-13 on 145.950 MHz I was able to locally translate the satellite at 145.250 MHz FM transmitting with 2.5 watt using another antenna to show locally the satellite performance without desensing the bird.
This setup is obviously permanently tuned and devoted for receiving the 70 cm and 2 meters satellite bands and it works.
73" de
i8CVS Domenico
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