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Re: System NF Calculations



-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
>
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>
> "The large print giveth
>  and the small print taketh away..." Tom Waits.
>
>
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