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

[Bruce Griffiths]

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.


Bruce