[time-nuts] Thermal noise contribution to phase noise

Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Jan 15 21:04:06 UTC 2013


As Bob stated thermal noise is equally divided between AM and PM 
components when a carrier is present.

Both  the AM and PM noise components are -177dBm/Hz their sum is 
-174dBm/Hz.

Bruce

Graham / KE9H wrote:
> 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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