At 12/17/2005 10:15, you wrote:
>I've got the same setup. I also have a 4-section
>Celwave bandpass filter between the duplexer and
>preamp. I found that the 17dB gain was way too much
>for the receiver, and the noise level increased
>dramatically, to the point that I had to tighten the
>squelch settings. The sig strength metering went from
>10 to 14uA with no signal.
Why is that such a bad thing? If you add a preamp to a RX & your measured
noise power doesn't increase, it means that the largest source of noise in
your system is still your RX & that there's still room for improvement.
Unless you're really worried about dynamic range, the ideal setup would be
one in which the total noise power added by the addition of the preamp
equals the noise present at the front end of the RX. This should provide
the best balance of system noise figure & dynamic range. If a 10 to 14 uA
change represents 3 dB, then you'd be all set at that point.
I don't know what's up with your carrier squelch. A well-designed squelch
circuit shouldn't care how much noise power is present at the front
end. Perhaps there's another problem with the RX: low gain in an IF stage,
limiter problem, etc. that's causing the discriminator output to change
with input noise power.
Bob NO6B
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