Hi This is one of those interesting areas where a broadband measurement (like a counter) and a narrowband measurement (like a DMTD) will give very different results. The counter will see the sub-harmonic, and call it jitter. It can show up in an ADEV calculation. A DMTD will ignore the sub-harmonic, and show no added jitter. With a DMTD, the ADEV will look fine. A PLL multiplier will (likely) also ignore the sub-harmonic, the jitter will not show up if you use the 10 MHz as a counter timebase in a HP counter.
Which one's right / does it matter - as always, that depends on what you are trying to do with the signal. Bob On Nov 18, 2012, at 1:26 PM, Volker Esper <[email protected]> wrote: > > @Azelio: Yes, (like Bob told) it's the phase lock, that locks the two maxima. > Actually the counter is able to look between the 60ps spaced towers, have a > look at the pictures in the first mail of this thread. However, there is a > smallest time value the counter can determine, but it is much smaller than > 60ps. > > Volker > > > > Am 18.11.2012 17:11, schrieb Bob Camp: >> Hi >> >> The 5 MHz and 10 MHz are "locked together" by the multiplier. Their relative >> phase is fixed. The 5 MHz component is not free to wander independently >> relative to the 10 MHz. Since it's a doubler, you get a two peak plot. If >> it was a X3 you would get three peaks. It really only makes sense if you >> look at it on a scope. Of course at 60 ps, it would have to be a mighty good >> scope. Much easier to see when the sub-harmonic is a bit stronger... >> >> Bob >> >> On Nov 18, 2012, at 9:53 AM, Azelio Boriani<[email protected]> wrote: >> >>> Interesting this, but why exactly 60pS? I would expect also something >>> in-between. That is, to have the 5MHz energy 64dB below, in my opinion >>> nothing prevents to have the edge to wander not only at 60pS but >>> continuously between 0 and 60pS. Maybe the SR620, being a 25pS resolution >>> counter, simply doesn't see what's going on in-between and the resulting >>> histogram looks that way. >>> >>> On Sun, Nov 18, 2012 at 3:51 AM, Bob Camp<[email protected]> wrote: >>> >>>> Hi >>>> >>>> A little more detail: >>>> >>>> What's going on is more clear if you trigger a scope on the positive edge >>>> of the 5 MHz and look at the 10 MHz. With an ideal multiplier, both the >>>> positive and negative edges of the 5 MHz should line up exactly with a >>>> positive edge of the 10 MHz. In reality, negative edge (the one not >>>> triggered) does not quite line up. It's a bit ahead (or behind) the ideal >>>> location. Since it's a small angle, the delta in phase and delta in >>>> amplitude both follow the same basic law. >>>> >>>> Bob >>>> >>>> >>>> On Nov 17, 2012, at 9:36 PM, Bob Camp<[email protected]> wrote: >>>> >>>>> Hi >>>>> >>>>> Just good old Fourier series. >>>>> >>>>> Bob >>>>> >>>>> On Nov 17, 2012, at 9:12 PM, Volker Esper<[email protected]> wrote: >>>>> >>>>>> >>>>>> I'm impressed - but what law is behind this? >>>>>> >>>>>> >>>>>> Am 17.11.2012 21:26, schrieb Bob Camp: >>>>>>> Hi >>>>>>> >>>>>>> 60 db isn't to bad a number. More or less: >>>>>>> >>>>>>> 100 ns -> 100 ps is 1000:1. 20 log of that is 60 db. 100 ps to 60 ps >>>> is about 4.4 db. That would sum up to -64.4 dbc. The main gotcha is that >>>> you *might* also have some 15 MHz (and higher) energy in the signal as >>>> well. Also phase gets into the calculation. Still, pretty close. >>>>>>> >>>>>>> Bob >>>>>>> >>>>>>> On Nov 17, 2012, at 12:50 PM, Volker Esper<[email protected]> wrote: >>>>>>> >>>>>>>> >>>>>>>> So let's have a look into the machine... and what do we see? There's >>>> a nice little Symmetrcom oven, with the sign reading "5.000 MHz" - bingo! >>>>>>>> >>>>>>>> May be there's a time saving way to determine the energie of the sub >>>> harmonic: using my spectrum analyzer. It tells me, that there's a 5 MHz >>>> subharmonic at the level of -62dBc. >>>>>>>> >>>>>>>> How would you have calculated the energy? What would be your ansatz? >>>>>>>> >>>>>>>> Thanks so far >>>>>>>> >>>>>>>> Volker >>>>>>>> >>>>>>>> >>>>>>>> Am 17.11.2012 17:55, schrieb Bob Camp: >>>>>>>>> Hi >>>>>>>>> >>>>>>>>> That's what you get if you have "sub harmonic" energy in the output >>>> of your OCXO. I'd bet you a warm glass of beer that you have a 5 MHz / >>>> doubled to 10 MHz MTI OCXO in your Z3805. If you have a lot of time on >>>> your hands, you can calculate the likely level of the energy from the >>>> amount of jitter (spacing between the two peaks) you get. >>>>>>>>> >>>>>>>>> Bob >>>>>>>>> >>>>>>>>> On Nov 17, 2012, at 11:41 AM, Volker Esper<[email protected]> >>>> wrote: >>>>>>>>> >>>>>>>>>> Hi, >>>>>>>>>> >>>>>>>>>> while playing with my recently aquired TIC (SR620) and measuring >>>> the period time of some oscillators I discovered something I hadn't expect >>>> at all: >>>>>>>>>> >>>>>>>>>> The output of my GPSDO (Z3805) writes two maxima in the period >>>> histogram (at a spacing of 60ps). >>>>>>>>>> >>>>>>>>>> I didn't believe that result and assumed an inherent error in my >>>> measuring setup or the counter itself. >>>>>>>>>> >>>>>>>>>> So I plugged another oscillator, the reference TCXO of my signal >>>> generator (R&S SMX), and that result made me happy and uneasy at once: The >>>> TCXO hat only one maximum. >>>>>>>>>> >>>>>>>>>> I havn't calculated the ADEV curve, yet. >>>>>>>>>> >>>>>>>>>> See pictures. >>>>>>>>>> >>>>>>>>>> Why does my GPSDO produce such a weird result? >>>>>>>>>> >>>>>>>>>> Cheers >>>>>>>>>> >>>>>>>>>> Volker - DF9PL >>>>>>>>>> >>>> <DSCF1437_bbb.jpg><DSCF1439_bbb.jpg>_______________________________________________ >>>>>>>>>> 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. >>>>> >>>>> >>>>> _______________________________________________ >>>>> 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. _______________________________________________ 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.
