# R: System NF Calculations

• Subject: R: [amsat-bb] System NF Calculations
• From: "i8cvs" <domenico.i8cvs@xxxxxx>
• Date: Mon, 21 May 2001 14:56:12 +0200

```The formula for NF calculation of my previous message must be corrected with
the following one because i
missed a square in to the numerator.The actual formula is correct
Apologise from i8CVS Domenico

----- Original Message -----
From: i8cvs <domenico.i8cvs@tin.it>
To: Bill Hurlock <bill@hurlock.net>; Scott Townley <nx7u@arrl.net>
Cc: Joe Leikhim <jleikhim@nettally.com>; AMSAT-BB <amsat-bb@amsat.org>
Sent: Monday, May 21, 2001 1:03 PM
Subject: R: [amsat-bb] 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    2
>                                          ( 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.
> >
> > > ----
> > > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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> >
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >
>
>
>
>
>
>
>
>

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