[amsat-bb] Re: NIST Phase Noise Measurements Group Noise Figure
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.
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.
Mario Lorenz Internet: <ml at vdazone.org>
Ham Radio: DL5MLO at DB0ERF.#THR.DEU.EU
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