Even if the -3dB were an issue, I'd have much more faith in a clear, passive resistor network than in a complex amplifier with all it's unknown non linear characteristics, temperature dependent time delays, noise sources, etc., etc. This simple home made network is a useful, manageable gadget. Volker
> Bob Camp <[email protected]> hat am 10. März 2014 um 01:47 geschrieben: > > > 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 <[email protected]> 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 <[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. > > _______________________________________________ > 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.
