[amsat-bb] Pre-Amp Help

David Mennerich david.n2teb at gmail.com
Tue Oct 4 01:23:33 UTC 2016

Hi Zach - I checked out that article and to my surprise I had a Comet
CF-416 duplexer sitting in my box of radio parts down in the basement.  I
did a quick test of the setup down in my basement and was able to easily
reproduce the desensitization scenario.  Then I changed the wiring and ran
from the antenna to the duplexer to the pre-amp to the radio.  No more

I will fully test this out the next time I set up my portable satellite
station - hopefully this upcoming weekend.

Thanks to all of those that replied to me - I have other ideas I can
experiment with as well based on your emails, but I'll start with this one
and see if it works for me.

73, Dave

On Mon, Oct 3, 2016 at 6:26 PM, Zach Metzinger <zmetzing at pobox.com> wrote:

> On 10/03/16 17:10, David Mennerich wrote:
> > I recently purchased an Advanced Receiver Research 2M pre-amp to use when
> > operating on the LEO SSB satellites.  I purchased the SP144VDG (24 db
> gain,
> > <1 NF).  They don't offer the lower gain, higher noise figure 2M pre-amps
> > anymore.
> >
> > I tried setting it up this weekend and when the pre-amp is on and I'm
> > transmitting on the 70cm band, I'm getting a lot of audio distortion.
> When
> > I tried this during a pass, my audio on 2M was barely readable because it
> > was so distorted, but with the pre-amp off, I sounded fine.
> It sounds like the active devices in your 2m LNA is getting crushed by
> the output of the 70cm transmitter.
> You could try "A Simple Desense Filter for Mode-J Satellites" in
> reverse: you want to put the preamp and radio on the 2m side and leave
> the 70cm side unconnected.
> http://www.amsat.org/?page_id=2136

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