[amsat-bb] Re: New Preamp

Bob Stewart bob at evoria.net
Tue Sep 18 17:00:50 PDT 2007


--- i8cvs <domenico.i8cvs at tin.it> wrote:

> The important of the point is that even if the lowest noise factor F1
> do not correspond to the maximum gain the gain G1 obtained from it be
> sufficient to get a satisfactory overall noise factor Ft of the system as
> the formula for more stages in series is showing:
> 
>                   F2-1       F3-1
> Ft = F1 + --------+ --------- + ..................
>                    G1       G1xG2

This is in the Satellite Handbook, and the example calculations on 
page 11-2 were a big part of my decision to get the preamp.  
Example 3 is very similar to my situation, so it seemed reasonable 
that my overall NF would drop noticeably.  Yes, the noise as displayed 
on the S-meter is about 5 S-Units higher.  However, the signal is 
even higher still.  The net is that I turn my volume control down on 
SSB and have more readable audio.  I haven't experimented with the 
RF gain control on FM yet to see if it lowers the noise floor and improves
quieting.


Bob


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