[amsat-bb] Re: fun with preamps

David - KG4ZLB kg4zlb at googlemail.com
Mon Mar 15 18:10:35 PDT 2010


I have been running both the Icom pre-amps with my 910 for some time now!

I do not need S/N ratio's or fancy tests to know that without them I 
would have missed many a contact;

True, they are not brilliant (Icom does not even publish figures for 
them)  but they work and unless I feel like chucking the thick end of a 
large amount of green at something else, they will continue to work.

And a large plus is that you can tx through them without fear of 
goobering them up and they operate through the coax so no messy power 
line runs with the coax!

Just my 2 cents worth of course!


On 3/15/2010 20:31, i8cvs wrote:
> ----- Original Message -----
> From: "Bob- W7LRD"<w7lrd at comcast.net>
> To:<amsat-bb at amsat.org>
> Sent: Tuesday, March 16, 2010 12:28 AM
> Subject: [amsat-bb] fun with preamps
> 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.
> Hi Bob, W7LRD
> No preamp noise Smeter=0, preamp on Smeter=7 means very small. Step 1
> without preamplifier tune your receiver in SSB or CW on a very weak carrier
> like a beacon and rotate your antenna into a null until you can barely hear
> a bit at about 1000 Hz over the noise. Step 2 now connect your preamplifier
> and see by hears if the Signal to Noise ratio S/N improves or not. If you
> can hear better the 1000 Hz bit your preamplier is useful othervise S meter
> = 7 means only or mostly the amplified preamplifier noise.
> Your test can be more accurate if instead to use your hears you connect an
> analog AC voltmeter at the audio output of your receiver.More is  the swing
> of the AC voltmeter and better is the preamplifier i.e. lover is it's Noise
> Figure.
> Have fun.
> 73" de
> i8CVS Domenico
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