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R: System NF Calculations



Hi  Bill,

The FT-736 sensitivity in CW/SSB with 2500 Hz bandwidth  is -15 dB microvolt
for a  ratio of  (S+N)/N  = 12 dB
from here:

10 log     ( -15/20 )  = 0,177 microvolt
           10

This is the applied voltage across the receiver input necessary to obtain
an output with a ratio  of  (S+N)/N = 12 dB



                                                                (12/10)
(S+N)/N =12 dB is  equivalent to 10             = 15,84   in factor

                      S+N
and   S/N = --------   -1  =15,84-1= 14,84  in factor
                         N

The noise figure in dB can be readily calculated using the following formula
derived from an article published in Ham Radio Magazine April 1980 page 71
and 94 and titled "Noise Figure Relationship"

                                                        -6
                                         ( 0,177x10    ) x 20
NF (dB) = [  10 log        -----------------------    ] + 174    =
                                10         2500 x 14,84


= -167,7 + 174 = 6,27 dB

In this formula 20 is a constant and 174 is the -174 dBm available thermal
noise power density (dBm in 1 Hz at room temperature) and 2500 is the
bandwidth in Hz



73 de i8CVS Domenico


----- Original Message -----
From: Bill Hurlock <bill@hurlock.net>
To: Scott Townley <nx7u@arrl.net>
Cc: Joe Leikhim <jleikhim@nettally.com>; <amsat-bb@AMSAT.Org>
Sent: Sunday, May 20, 2001 11:56 PM
Subject: Re: [amsat-bb] System NF Calculations


> I looked at the manual for the Ft-736R and it says for cw/ssb better than
> -15dbu for 12 db S=N:N. What does that make it.
>
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