Bruce,
[EMAIL PROTECTED] wrote on 12/08/2008 05:53:08 PM: > 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. Single diode? Why wouldn't one use a standard (MiniCircuits or the like) four-diode two-transformer double-balanced mixer as the phase detector? Many mixers have IF response down to DC. > 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. Dual mixer as in DMTD (dual mixer time difference) would certainly work, but is pretty complex and temperature sensitive. I did use a loaner Symmetricom 5120A (a full digital DMTD implementation) to make some measurements six months ago, and after a few days of continuous operation it had settled to the point that one could see 0.01 pS changes. (And touching one of the BNC connectors caused a 1-3 pS jump.) This instrument costs about $30K, and is intended more for measuring phase noise and allan variance than delay changes. Anyway, I have to wonder what people did before DMTD was invented. > 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. I've read many or most of the classical DMTD papers, and have seen various passing estimates that diode-ring mixers have a temperature sensitivity of 8 to 10 pS per degree C. (I recall your figure was 10 pS/K.) I assume that the DC offset also varies with themerature and drive signal amplitude. > 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). Is the sound-card approach workable at the millidegree to microdegree level, if the change is spread out over an hour? One picosecond at 10 MHz is 3.6 millidegrees of phase. Joe _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
