John, When you add two (statistically independent) 5 MHz signals and get a 10MHz signal, the 10 MHz signal's *relative* noise and drift will be the average of the *relative* noise and drift of the two 5 MHz signals. So as when you average n signals, the noise and drift are reduced by sq.rt of n, in this case, 1.4, or about 2dB (if I am correct), a modest improvement.
Combining more than 2 signals that way (to get more than 2dB improvement) gets complicated in a hurry. I guess the idea behind differential locking was to simplify the circuit so that a large n could be used to get meaningful improvement without too much additional circuitry. Didier KO4BB > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Magnus Danielson > Sent: Tuesday, December 23, 2008 12:03 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] New topics (was Re: He isa Time-Nut > Troublemaker....) > > John Ackermann N8UR skrev: > > Magnus Danielson wrote: > > > >> This diffrential locking technique could be applied to atomic > >> standards, but then naturally require much improved solution than > >> simple oscillators. The diffrential locking technique does not > >> magically solve issues that is typically common mode, such as > >> temperature dependence. It can however even out individual > properties > >> like noise and systematic drift to some extent. It > essentially runs > >> the oscillators as a common constellation and attempts to > achieve the > >> average improvements of those oscillators in an > interlocked fashion. > >> In its simplicity it will do unweighed averaging. It is > fairly easy > >> to do weighed averaging by individualizing the feedback > gain to the > >> respective oscillators. Further refinements would > individualize the > >> proportional and integrate feedback terms, but as always, > the simplicity forms a limit. > > > > Assuming that the atomic standards are correct for some > tolerance of > > "correct", I'm not sure why you would need to use a differential > > locking scheme (or anything else that moves one oscillator > versus the > > other) -- if you simply mix the two signals together you get a sum > > that contains both signals. Apart from redundancy (what if > one unit > > fails), why not just use that sum to drive the clock? > > Because they _WILL_ drift appart. > > Interlocking them force them to a common frequency and average phase. > > Cheers, > Magnus > > _______________________________________________ > 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. > _______________________________________________ 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.
