[time-nuts] How do time-nuts measure phase noise?

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Aug 17 15:24:12 UTC 2009


The mixer output is only sensitive to phase differences for small
deviations about 90 degrees phase difference between the 2 sources.
With unlocked sources AM noise also affects mixer output.
In order to measure phase noise without phase locking you need something
like a COSTAS receiver or equivalent.
For detail on one approach to this download and read the Symmetricom
5120A manaual.

Bruce

iovane at inwind.it wrote:
> In order to simplify the project, and given that I wouldn't need to distinguish 
> what source the noise comes from, I could use only S1 and X sources. And here is 
> my last question. If I don't lock the sources to one another (say two HP 10811), 
> what is the unconvenience? An additional signal in the spectrum, or something else 
> that I don't figure now?
>
> Thanks and kind regards,
>
> Antonio I8IOV
>
>   
>> Some have commercial phase noise measurement systems like Symmetricoms
>> 5115A, 5120A. 5125A.
>> Some have older HP phase noise measurement systems like the 3048A etc.
>> The rest of us have to build our own systems based around sound cards or
>> surplus spectrum analysers together with the necessary mixers, low noise
>> amplifiers etc.
>>
>> Unless your sources are very noisy you wont be able to measure their
>> phase noise with just a selective voltmeter or even an RF spectrum analyser.
>> If you cant build it, then you need to acquire something like the HP3048
>> or the NIST phase noise measurement box currently on ebay.(Item:
>> 260423038423)
>>
>> Bruce
>>     
>
>
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