[amsat-bb] Re: AMSAT Broadband Preamp Specs

Paul Stoetzer n8hm at arrl.net
Thu Oct 3 09:02:02 PDT 2013


Thanks for the "real world" example. My receiver is an Icom IC-R10, 
which the specifications say has a 0.25 uV sensitivity on 144 MHz and 
0.32 uV on 435. I operate portable, so I'm not using the preamp for the 
high gain to overcome cable loss, but to overcome the relatively high 
noise figure of the receiver. The preamp works great for FO-29. When I 
have a clear horizon, I can hear it down to 1 degree or so with an Arrow 
antenna. My problem is the horizon (and a military spread spectrum 
radiolocation system that causes "clicking" noises all over the 70cm 
band here in Washington).

On 2m, the preamp also helps greatly, but the preamp also amplifies 
countless out of band signals that desense the receiver. I have a PAR 
electronics notch filter to notch out the pagers at 152 MHz (two 
kilowatt pager transmitters are a quarter mile away from me), but that 
doesn't completely eliminate the problem. I have used a 10 dB attenuator 
between the preamp and receiver which eliminates the desense, but also 
reduces the signal level a bit too much. A 6 dB attenuator should arrive 
in my mailbox shortly and I'll try it on the next pass of AO-7 this 

What I likely really need to add is some low loss bandpass filtering for 
2 meters, but it needs to be small since I operate with everything in a 
DSLR bag carried around my neck. Any suggestions?

Ultimately the only perfect solution is a second FT-817 to use as the 
receiver, but that's not in the cards at the moment.


Paul, N8HM

On 10/3/2013 11:22 AM, Alan wrote:
> Paul,
> Spence did some rough testing, but it was designed to be simple, cheap, robust, and easily duplicated
> rather than cutting edge.  I did some A/B testing with an ARR preamp on SO-50 and FO-29.  Both made
> significant improvement, and I did not hear any practical difference.  That would not likely be the
> case if we were talking about P3 bird at apogee.
> 73s,
> Alan
> <-----Original Message-----
> <From: amsat-bb-bounces at amsat.org
> <[mailto:amsat-bb-bounces at amsat.org] On Behalf Of Paul Stoetzer
> <Sent: Thursday, October 03, 2013 5:40 AM
> <To: amsat-bb at amsat.org
> <Subject: [amsat-bb] AMSAT Broadband Preamp Specs
> <
> <I was curious - has anyone measured the noise figure and gain of the
> <AMSAT Broadband Preamp?
> <
> <73,
> <
> <Paul Stoetzer, N8HM
> <Washington, DC
> <_______________________________________________
> <Sent via AMSAT-BB at amsat.org. Opinions expressed are those of
> <the author.
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