[time-nuts] Thermal noise contribution to phase noise

Graham / KE9H timenut at austin.rr.com
Tue Jan 15 20:45:30 UTC 2013


Bruce:

The last time I looked, the thermal noise floor was still -174 dBm/Hz 
(at 300 Kelvin).

http://en.wikipedia.org/wiki/Thermal_noise

Are you saying Boltzmann's constant is off by 3 dB, or are we mixing 
apples and oranges here?

Is there a 3 dB adjustment between noise floor (at room temperature) and
the "single side band" phase noise measurement, which only looks at half
the noise, since it only looks on one side of the reference signal?

--- Graham / KE9H

==

On 1/15/2013 1:38 PM, Bruce Griffiths wrote:
> I've noticed a disturbing tendency to quote the thermal noise 
> contribution to phase noise as -174dBm/Hz instead of the corrent value 
> of -177dBm/Hz as verified by measurement by NIST:
> http://tf.nist.gov/phase/noisemeas.html
>
> This error occurs in papers from Spectrum Microwave, Wenzel Associates 
> and others.
> Blindly propagating the results quoted in the early literature isnt 
> particularly helpful given that the definition of SSB phase noise has 
> changed in the intervening decades.
>
> Bruce
>





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