# Re: System NF Calculations

• Subject: Re: [amsat-bb] System NF Calculations
• From: Joe Leikhim <jleikhim@xxxxxxxxxxxx>
• Date: Sat, 19 May 2001 16:01:13 -0400

Thanks Scott;

Does the second part of the equation (bandwidth) come into play when the
manufacturer is stating a spec reference SSB/CW? I know there is a difference
due to the bandwidth, it just seems the manufacurers are not telling the whole
story by spec'ing this way. ARRL is further confusing things by using "MDS"
measurements when they evaluate new products.

Those of us without lab grade facilities are at a disadvantage when it comes
to pinning down these numbers.

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
>
> ------------
> "When the Going gets Weird, the Weird turn Pro"
> Raoul Duke, Sportswriter
>
> "Don't worry Boys, we'll weather this Storm of Approval and come out as
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>
>

--
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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