Hi Do you routinely do arc welding while waiting for an ADEV plot to finish :)… (I drink beer, but not everybody is into that …)
You might consider trying a passive splitter on one of the outputs of the GPSDO. There aren’t many ways they will mess up a signal other than by dropping it’s level. If level is a concern then indeed they could be an issue. Bob On Mar 9, 2014, at 6:17 PM, Magnus Danielson <[email protected]> wrote: > On 09/03/14 22:36, Volker Esper wrote: >> Am 09.03.2014 19:46, schrieb Magnus Danielson: >>> On 04/03/14 01:05, Volker Esper wrote: >>>> Am 03.03.2014 23:04, schrieb Magnus Danielson: >>>>> Volker, >>>>> >>>>> 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 closer. >>>>> >>>>> 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. >>>>> >>>>> 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. >>>> I already did these measurements, I stick the plots at this posting. >>>> >>>> - The plot with the long file name shows frequency mode measurement: >>>> 10MHz external reference put into channel A. >>>> - "...Plot2" shows a phase measurement, where I fed the reference signal >>>> via a home made 50 ohms splitter into both input channels. (I prefer >>>> feeding the channels symmetrically) >>>> Both plots show linear negative gradients, but the phase plot is >>>> steeper. The frequency plot transitions into a horizontal at about >>>> 1000s. >>> >>> The 1/sqrt(tau) curve is higher than the background noise of the >>> counter. That flicker phase noise is more typical of a buffer or >>> source than of the counter. >>> >>> For shorter taus I would expect the white noise to dominate. >>> >>> I'm just surprised about the level of flicker phase noise. What is the >>> source? >>> >>> 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. >> >> Source in both cases is an HP Z3805 GPSDO. I didn't insert an additional >> buffer, however, the Z3805 has two (buffered) outputs. I used one for >> counter reference, the other one for counter input. > > Hmm... what is the noise when you measure it on the SR620 itself? > > It seems a little high here. > > 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.
