[amsat-bb] Re: fun with preamps
stanw1le at verizon.net
Mon Mar 15 17:02:54 PDT 2010
Does the preamplifier have a internal gain control ?
If it does, back it off at ~ 6 S units.
Excess gain only reduces the system dynamic range.
The real test is with a SINAD meter or a NF meter, injecting a test
signal up at the preamplifier input,
and reducing gain until NF or SINAD sensitivity is just barely degraded.
That will be the point of best S/N, (best sensitivity).
Most of the S7 reading you have is just noise, not signal.
The preamplifier could be defective and performance is out of spec.
Whatever that spec is, I do not recall ever seeing a ICOM AG-25/35
If the preamplifier is a multi stage unit, the first stage which sets
the system noise figure
could be defective/soft and the second stage just amplifies the noise
ahead of it.
Most convincing would be a NF test with professional meter.
Send it to me and I will test for free. I will NOT repair. I will NOT
Include return postage if you want it returned (HI).
I will provide you a plot of the NF and gain performance using
a HP-8970B Noise Figure Meter and HP-346C Noise source.
Of course, this offer is open to any other AMSAT member.
E-mail me for details.
What do you say ?
Stan, W1LE Cape Cod FN41sr
Bob- W7LRD wrote:
> Just installed a AG-25 (Icom preamp) on my 2M cp yagi. No preamp noise Smeter=0, preamp on Smeter=7. Signals "appear" better after backing down the volume with the preamp. I have 8-10 feet of LMR400uf from antenna to preamp, 50 feet of LMR400 to shack. I suppose I was expecting more "dramatic" results, I realize the AG-25 isn't the greatest and best, but it works well with the 910. Are these real world results for what I have. S7 noise level seems a bit high.
> as always-thanks
> 73 Bob W7LRD
> Sent via AMSAT-BB at 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
More information about the AMSAT-BB