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

[Steve Rooke]

2009/8/17 Bruce Griffiths <bruce.griffiths at xtra.co.nz>:
> iovane at inwind.it wrote:
>> Please, how do time-nuts measure phase noise? What may be a minimal setup whit recording capability?
>> Thanks,
>> Antonio I8IOV
>>
>>
>>
> A minimal setup for the classical method requires 2 frequency sources at
> the same frequency one of which can be phase locked in quadrature (with
> low loop bandwidth) with the other.
> The output spectrum of the phase detector outside the PLL loop bandwidth
> is then proportional to the relative phase noise spectrum of the 2
> sources and is measured using a spectrum analyser.
> A double balanced diode mixer is used as a phase detector (most other
> types of phase detectors are far too noisy).
> A sound card with a suitable low noise preamp can be used as an FFT
> based spectrum analyser in the ~10Hz to ~20kHz range, the actual
> frequency limits depend on the sound card and its sampling rate.

So how do you discriminate against the phase noise of the source you
are using as a standard frequency? Do you have to use a known low
phase noise standard to mix with your unknown source?

Steve

>
>
> Bruce
>
>
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-- 
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.