[amsat-bb] Re: NIST Phase Noise Measurements Group Noise Figure

Mario Lorenz ml-ams at vdazone.org
Sat Jan 19 11:03:31 PST 2013

Am 18. Jan 2013, um 23:46:39 schrieb Joe Leikhim:
> I have just sent off an e-mail to David Howe of NIST Metrology
> requesting clarification.
> I was shocked when I first saw this and posted it a couple places to
> get feedback.
> Domenico's excellent response further demonstrated that explanation is required.

Dear Joe,

Tthe -177dBm/Hz value pertains to Phase noise (PM),
which is in case of stationary (like thermal white) noise half of
the total noise power ( -174 dBm/Hz - 3dB down.)
(the other half is amplitude noise, which is not considered in
the paper there).

Changing kTB (total thermal noise power) mathematically requires
either changing B (but this is fixed to 1 Hz by the resulting unit)
or T (halving the temperature, but this is not stated in
the paper, nor would it make practical sense), or k (significantly
changing a fundamental physical constant takes more than a single
NIST paper and would have more profound effects than requiring
recalibration of all NF meters :).

The other topic of the paper is that Noise Figures as usually
used in the low signal case to characterize the thermal noise
properties of the amplifiers may not be a good figure of merrit in the
the strong signal case, the phase noise caused by intermodulation
between the carrier and the noise may actually dominate there.

Best 73s,


Mario Lorenz                            Internet:    <ml at vdazone.org>
                                        Ham Radio:   DL5MLO at DB0ERF.#THR.DEU.EU

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