Hi The gotcha is that the injection gain is phase angle dependent.
Bob On Jun 16, 2010, at 1:57 AM, Magnus Danielson wrote: > On 06/16/2010 05:45 AM, Charles P. Steinmetz wrote: >> Warren wrote: >> >>> Charles posted: >>>> but the locked frequency will be different from both oscillators' >>>> free-running frequency and >>>> the EFC will not correctly indicate the test oscillator deviation >>>> because it isn't the only control input in the system. >>> >>> Good point and No argument (except for the deviation part) >>> Because the EFC is the only control input THAT IS VARYING. >> >> No, it's not. The strength with which each oscillator pulls on the other >> also varies as the equilibrium frequency (the result of all three >> recursive control inputs) moves around relative to the two instantaneous >> free-running frequencies. How much EFC is required depends, in part, on >> the strength of the pulling. There are three varying inputs. >> >> Magnus suggested that the effect of injection locking may be enough >> smaller than the EFC input that it has little practical significance. >> That may be so, but when dealing with measurement accuracy in the >> hundreds or tens ot ppt, this needs to be verified by the results of >> carefully constructed experiments and hopefully also supported by >> mathematical analysis. > > What you get is a scale error. Consider that you have an amplifier gain of > 1000 and the injection locking provide a gain of 1, that will result in > actual gain of 1001 and the gain error on the EFC will become 1000/1001. > Considering that Allan deviation estimation has problem of its own, this > scale error is not significant. What you do need to check is that the > relationship between intended gain and injection gain is sufficiently > different. Since oscillator frequency from EFC may not be completely correct, > we already want calibration of that scale factor (K_O) and the gain error due > to injection locking would be included into that correction factor. > > So, sufficiently small amount of injection locking gain will change the > apparent EFC coefficient K_O [Rad/sV] on which the scale of TPLL frequency > measurements depends. The fractional frequency observed is > > y(t) = 2*pi*f_0 / K_O,eff EFC(t) > > Cheers, > Magnus > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
