Have you guys tried the Simrex (formerly GLB) helical resonator pre-amp? It's great for repeater applications. Very selective and moderate gain. If you're using Bp-Br type cans you don't need any further filtering.
I haven't bought one in quite a few years, but the last one I got was in the $150 range.
Dan N8DJP
Date: Sun, 18 Dec 2005 08:26:10 -0800
From: [EMAIL PROTECTED]
Subject: Re: UHF Preamplifier
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
From: [EMAIL PROTECTED]
Subject: Re: UHF Preamplifier
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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