[time-nuts] ADEV from phase or frequency measurement
magnus at rubidium.dyndns.org
Mon Mar 3 17:04:11 EST 2014
On 03/03/14 00:50, Volker Esper wrote:
> Sorry for the "time delay"...
> TIC: SR620 with Z3805 as external reference; signal source
> Nortel/Trimble GPSTM (GPSDO) 10MHz output
> Enclosed two plots (SW: "Plotter"):
> - one is sigma(tau) calculated from phase samples (SR620 TIME mode),
> - the other one is sigma(tau) from frequency data (SR620 FREQ mode)
> Whole equipment had a power up time of several days/weeks. Room
> temperature was stable over both measurements (within about 2 degrees C).
The SR620 uses a bit different path through the logic when doing TI and
FREQ measurements. The frequency measurement has a "feature" that means
that the time error between start and stop signal needs to be calibrated
out. This can be done using the calibration routines given in the
manual. This should not affect the ADEV measure, but as a precaution.
Try doing a pair of noise-floor measurements. That is, feed the
reference 10 MHz to the A input for the frequency noise measurement.
Then, for the TI noise-floor measurement, put a T on the A input, put it
in high-Z mode and then use a 1 m cable to put the signal onto the B
input which is terminating.
You indeed have a higher level. Your initial shape makes me wonder. I
would really like to get the TimeLab measurement files and eye-ball them
If you plot the phase or frequency, it may be easier to spot systematic
wobbles. TDEV would also help, as it provides a general *tau scaling to
the ADEV plot.
More information about the time-nuts