Bruce, > When measuring the frequency of a signal using a conventional counter, > increasing the gate time decreases the noise contribution of trigger > jitter to frequency measurement noise although jitter is invariant with > gate time. The jitter simply becomes a smaller fraction of the total > gate time. Similarly the frequency measurement resolution increases with > increasing gate time although the resolution (measured in picoseconds) > is invariant with gate time it simply becomes a smaller fraction of the > total gate time.
True, I was being a bit sloppy there... > However if one timestamps a few more signal zero crossings within the > gate time interval than just those and the start and end of the gate > time lower noise estimators of the frequency are available. Indeed. > The HP53132 averages the frequency estimates for a series of identical > duration overlapped gate times. > Enrico's paper analyses this case. > The Australian paper corrects some of the errors in Enrico's analysis > and hints how the analysis may be extended to cover the case of counters > that use other resolution enhancement techniques. Recommended reading! > Counters like the Pendulum CNT91 in effect time stamp every Nth zero > crossing of the signal and fit a linear regression line to the sequence > of time stamps. The frequency is then estimated from the slope of the > regression line. However the CNT91 has limited memory and processing > power so that full advantage isnt taken of the resolution offered by > this technique. > AFAIK no one has yet done a similar analysis to that done for the > "triangular" averaging counter (by Enrico and the Australians) for a > counter that does a regression line fit. Actually, as I recall it, there was a note in one of those articles relating to it, but your could figure out that it was rendering about the same conclusion. It also makes sense. 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.
