Bob, I sometimes indeed do arc welding, as well as forging... But that's another story.
When waiting for an ADEV measurement I sit still, trying not to move a millimeter. Seriously, I try to avoid any rf noise, e.g. ham radio, any airflow, any temperature change. I log supply voltages and check, if there's anything odd. I avoid any switching supply. I regularely check, if any switching voltage regulator (TV, monitors, PC,...) disturbs my rf ether... As the legends of my plots tell, I do use a passive splitter to get two similar signals (start and stop) for phase measurement. But I haven't used it for splitting the 10MHz for frequency measurement (reference and input). Lower level is a concern, since it increases phase jitter. Volker Am 09.03.2014 23:32, schrieb Bob Camp: > 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. _______________________________________________ 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.
