[time-nuts] Usefulness of high end counters for ADEV plots of oscillators

jpbridge at aol.com jpbridge at aol.com
Fri Jan 30 11:38:27 EST 2015

 Though I'm new to the list I've lurked for quite a while and from reading various posts I am in a slightly confused state as to whether buying an expensive counter (eg Keysight 53230A or a Tek fca 3100) will be useful as a measurement tool for developing a GPSDO.

Given a one shot measurement resolution of 50 psecs (on the Tek which is a pendulum CNT91) means that the uncertainty is around 50E-12 at 1 sec or 5 x 10^-11 or 10^-10 in round numbers for a ADEV at 1 sec? For this noise floor to get well below 10^-11 (the sort of ADEV of an OCXO) requires the interval to be increased to nearer to 100 seconds?

So does this mean that an expensive counter allows useful ADEV plots from 100 seconds on but not the lower time frames? (By useful I mean able to measure down to and below 10^-11 not down to 10^-14!)

The extra cost of the 53230A over the 3100 gets down to 20 psecs so possibly reduces the period to a bit less than 100 seconds but still above 10 seconds probably?

Does paying extra for an OCXO gain significantly on this basis?

Have I got the basic numbers right, and if one of my main aims is to have a good instrument for playing with GPSDO development will investing in such an expensive (for an individual hobbyist) instrument buy me a useful measurement capability or would it just be good for measuring long term frequency and say 1pps jitter from the GPS?

Sorry for the long post,




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