Hi So far, I have not found the 3db lost in a a passive splitter to be a problem with anything I have played with. With proper termination , they seem to be a good thing to use.
Bob On Mar 9, 2014, at 7:55 PM, Volker Esper <ail...@t-online.de> wrote: > 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 <mag...@rubidium.dyndns.org> >> 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 -- time-nuts@febo.com >>>>>>> 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 -- time-nuts@febo.com >>>>> 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 -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.