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

[iovane at inwind.it]

On Mon, 17 Aug 2009 23:18:58 +1200 Bruce Griffiths wrote:

> Steve Rooke wrote:
> > 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
> >>>

> >>>       
> >> snip

> 1) Use 3 sources, S1, S2 and X.
> 
> 2) Phase lock S1 in quadrature to X using a diode double balanced mixer
> using a low bandwidth PLL.
> 
> 3) Phase lock S2 in quadrature to X using a diode double balanced mixer
> using a low bandwidth PLL.
> 
> Then for frequencies outside the PLL bandwidth the crosspower spectrum
> of the 2 mixer outputs should be predominantly due to the phase noise X.
> 
> In practice its best if the phase noise of the 2 standards S1, S2 isn't
> significantly worse than that of X.
> 
> It is also desirable that both S1 and X and S2 and X be locked at their
> respective mixers quadrature point (not necessarily the same as that for
> zero dc output)
> 
> Bruce

Bruce,

is this what actually time-nuts do? This is unpractical for me, as I have not much 
time for a circuit building project. Moreover, I would be satisfied even with the 
analysis at a single frequency, not necessarily the whole phase noise spectrum, 
and with relative but repeatable measurements.
So, does it make any sense using a selective voltmeter, such as an HP 3586A or 
similar? 

Antonio I8IOV