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Re: System NF Calculations



That still seems high. The -126 dBm is at 10 dB S/N. If you calculate a system
noise figure and have a preamp with 18 dB gain (SP13-O) and some typical line
loss things degrade pretty fast.

hasan schiers wrote:

> -126 dBm corresponds to a NF of about 14 dB. I'm told that the FT-847 has
> been carefully measured at 14 dB with the preamp off. With it on, it
> measures 8 dB. If you are driving your radio with a mast mounted high gain
> downconverter like the UEK, or even a moderate gain surplus downconverter,
> you have to turn the preamp off...so use the 14 or 15 dB NF for the
> receiver...as bad as it sounds...it's right.
>
> The good news:  ...it doesn't matter. The sensitivity of your system is set
> by the NF of the 1st RF amp and that's way out at the antenna. Changing the
> NF of your radio from 15 to 5 produces virtually NO IMPROVEMENT in overall
> system NF, if you have a low noise figure, high gain 1 RF stage out at the
> antenna.
>
> 73, (the above comment ignores the antenna in making sensitivity
> comments...for the nit pickers)
>
> hasan
>
> hasan schiers, NØAN
> schiers@netins.net
>
> ----- Original Message -----
> From: "Joe Leikhim" <jleikhim@nettally.com>
> To: <amsat-bb@AMSAT.Org>
> Sent: Friday, May 18, 2001 10:35 PM
> Subject: [amsat-bb] System NF Calculations
>
> > 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.
> >
> >
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >

--
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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