# Re: System NF Calculations

• Subject: Re: [amsat-bb] System NF Calculations
• From: Bill Hurlock <bill@xxxxxxxxxxx>
• Date: Sun, 20 May 2001 17:56:33 -0400

```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.

Scott Townley wrote:

> I imagine that the spec is actually 0.11uV for 10dB (S+N)/N (which
> algebraically is S/N+1)
> So -126dBm @ 10log(9)=9.54dB S/N
> -135.54dBm @ 0dB S/N = FkTB (noise figure*Boltzman's
> constant*temperature*bandwidth)
> Take out the B (assume 2.5kHz) 10*log(2500)=34dB
> -135.54-34=-166.14dBm/Hz=FkT
> kT at room temperature -174dBm/Hz
> F=-166.14-174=7.84dB
>
> My FT-726R claims 0.15uV for 10dB (S+N)/N, which would be
> 20*log(.15/.11)=2.7dB worse (NF=7.84+2.7=10.54dB).
>
> But, if you have sufficient gain in front of the RX, then NF(RX) isn't too
> important.  One must work out the system noise figure calculation to
> determine "sufficient".
>
> At 11:35 PM 5/18/01 -0400, Joe Leikhim wrote:
> >What is a typical noise figure for a multi-mode radio?
> >The 15dB in the spreadsheet example sounds like pretty sorry
> >performance.
> >The ICOM radios are spec'd at about  0.11uv (-126 dBm) for 10dB S/N in
> >CW/SSB modes. How does that equate to NF and  MDS?
> >
> >--
> >Joe Leikhim K4SAT
> >Jleikhim@nettally.com
> >
> >http://www.ibiblio.org/jimmy/mcguinn/9000e.ram
> >
> >"tv dinner by the pool,
> >i'm so glad i finished school" -F.Zappa 1967
> >
> >"The Revolution will NOT be televised" -Gil Scott Heron
> >
> >"Whats he building in there?"- Tom Waits
> >
> >"The large print giveth
> > and the small print taketh away..." Tom Waits.
> >
> >
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> ------------
> Scott Townley
> nx7u@arrl.net
> Gilbert, AZ  DM43
>
> HF/VHF/UHF/Satellite MOBILE station
> http://www.primenet.com/~nx7u
>
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