# Re: System NF Calculations

```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?
>
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>Joe Leikhim K4SAT
>Jleikhim@nettally.com
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