Re: [amsat-bb] AO40 QRP zone?

["Edward R. Cole" <al7eb@xxxxxxxxxxxxx>]

>From: "Greg D." <ko6th_greg@hotmail.com>
>Hi Ed,
>
>Right now I have a Conifer preamp in front of my Drake.  The preamp
>is something like 1.5nf and 10db of gain.  Would it behave the
>same as your MMIC stage, if I just stick the DEM in front of it?
>
>There was a thread a couple of days ago that suggested putting
>two preamps in series didn't do much good.

Greg,

Cascading two preamps can work to give you additional gain, but it is easy
to overdrive the second preamp, especially if it is a low noise GasFet
device.  The second stage does not need as good NF as long as it is
reasonalbly good [<2 dB].  A regular jFet would be more tolerant here.  The
mmic works just fine as well.

For instance running a 30 dB gain preamp with a Drake having 15 dB gain
overdrives the internal preamp in my FT-847 and makes copy subtley worse.
I leave it off and though signals read lower s-units, they easier to hear!
I see the same  situation when I operate eme on 2m; the FT-847 is more
sensitive with the internal preamp off when using an external preamp. 

I would just try the Conifer and see if it seems to improve your hearing if
you have a DEM.  BTW the Conifer isn't too bad a preamp if you have a
fairly low NF converter [<3 dB].  A freind of mine used one with a Meyers
grill-type dish and a Drake with good  results.  He has upgraded to a DEM
preamp and converter, now.

Ed

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