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Re: Preamps



If you are adding a preamp in front of the Drake,  you might
consider adding a second-stage MMIC amp in the preamp itself,
instead of in the Drake.  

The advantages of this approach are:

1: The first-stage FET will see a more controlled
load impedance, reducing the chances NF deterioration or
oscillation.

2: The extra gain will prevent the attenuation in the cable
from the preamp to the convertor from hurting the system NF as much.
For me, this matters, because my convertor is about 8
feet from my antennas, out of the weather.

I am using a DJ9BV preamp which has a MGA86576 MMIC for
the second stage.  Because of this, I was able to remove 2
of the 3 MMIC amplifiers in my DEM downconvertor and still
have plenty of gain.

BTW, the Mode-S book describes a modified WB5LUA preamp.

Doug
NA1DB


At 04:46 PM 5/19/01 , you wrote:
>Jeff, Bdale Garbee, KB0G gave an excellent run down on this Saturday morning
>in Dayton.  He is using the Drake and recommends a preamp.  I picked up a
>DEM 13ULNA 2.4 gh preamp ($85 kit, $120 assembled) at the hamvention.  He
>presented figures showing this combination to be very comparable with the
>best as to gain and noise.  He did suggest the preamp be mounted directly on
>the antenna with a barrel N connector if you can do it.
>
>Mal, NP2L

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