Bob You should to use the same measurement bandwidth when comparing ADEV measures.
The measurement bandwidth of a Timepod is usually less than 1kHz whereas the 5370A has a trigger system bandwidth of 100MHz or so. If the high phase noise of your GPDSO isnt attenuated by a filter it may cause significant measurement noise. Bruce > On 05 March 2017 at 14:03 Bob Stewart <b...@evoria.net> wrote: > > OK, but how does the phase noise of the GPSDO make the ADEV for the Cs > worse than that for the GPSDO? I find it hard to believe that the phase > noise from two separate units would cancel out for two GPSDOs but add for the > Cs. > > Bob > > > > > --------------------------------------------- > From: Bruce Griffiths <bruce.griffi...@xtra.co.nz> > To: Bob Stewart <b...@evoria.net>; Discussion of precise time and > frequency measurement <time-nuts@febo.com> > Sent: Saturday, March 4, 2017 6:03 PM > Subject: Re: [time-nuts] Cs standard stability > > Bob > We are certainly not off track. > The phase noise of the GPSDO affects the trigger jitter of both the 5370A > and the jitter of the GPSDO PPS output and consequently the ADEV measured by > your setup. > NB ADEV depends on the measurement bandwidth which is relatively small > when using a Timepod. > Bruce > > > > On 05 March 2017 at 12:31 Bob Stewart <b...@evoria.net> wrote: > > > > Bruce, > > > > Are we getting a bit off track? The question I asked is in regards > > to the Cs, not the purity of the output of the GPSDO. The two ADEVs were > > done under the same conditions, yet the ADEV of the Cs is obviously not as > > good as that of the GPSDO. Also, the ADEV of the GPSDO pretty much tracks > > what is to be expected when run on a good 5370, isn't it? > > > > Bob > > > > > > > > --------------------------------------------- > > From: Bruce Griffiths <bruce.griffi...@xtra.co.nz> > > To: Bob Stewart <b...@evoria.net>; Discussion of precise time and > > frequency measurement <time-nuts@febo.com> > > Sent: Saturday, March 4, 2017 5:22 PM > > Subject: Re: [time-nuts] Cs standard stability > > > > Bob > > The Phase noise of that GPDSO seems quite high and some form of > > filtering (bandpass or low pass) of its output may be necessary to reduce > > the resultant jitter when connected to the 5370A input. > > There are commercial TDCs that claim that sort of performance > > (~10ps) but a comprehensive test of their actual performance appears as yet > > unavailable. > > HP used to sell a TDC with 5ps resolution but detailed specs are > > unavailable. > > Higher resolution and lower noise should be achievable but would > > require a lot of number crunching for each measurement. > > Bruce > > > > > > > > > > > _______________________________________________ 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.
