[time-nuts] Sub Pico Second Phase logger

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Dec 8 22:53:08 UTC 2008


Joseph M Gwinn wrote:
> People used passive mixers driving electromechanical stripchart recorders 
> to compare high-stability oscillators in the good old days.
>
> One assumes that there is a purely analog approach to measurement of 
> picosecond changes in delay at 10 MHz using a single oscillator, but I 
> have not seen any methods described, probably because the relevant 
> articles appeared many decades ago.
>
> Can anyone suggest some articles to read?
>
> Thanks,
>
> Joe Gwinn
>   
Joe

Although one could in principle do this with a single diode double
balanced mixer used as a phase detector all one may end up measuring is
the effect of ambient temperature changes on the mixer phase shift.
Lower mixer phase shift tempcos are possible if the RF port is unsaturated.
A classical dual mixer system is probably better in that with matched
tempco mixers maintained at the same temperature the differential phase
shift tempco should (with careful matching) be lower.

Other than the numerous classical papers on dual mixer systems and the
occasionl NIST paper that have some mixer phase shift tempco data
(albeit sparse), I am not aware of any specific papers.

A purely analog approach to phase shift measurement has to be more
difficult than a hybrid one using a pair of low frequency ADCs (eg high
end sound card).

Bruce




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