As far as lazy, I will check my equipment. When the others that replied using the term “lock” or “locked”, what do you mean by that? That for instance, the external reference is multiplied up directly to the internal frequency (IF I suppose) or is it phase locked, for instance? I’m sure there are other cases.
I’m trying to differentiate between two cases: 1) I apply an external reference at 10Mhz (assumed all the devices require 10Mhz at a certain level) and using a switch of some type (electronic or manual) the reference is now multiplied and manipulated directly to feed stages of the device. In this way, the phase noise of the device is very much dependent on the external reference. So if a noisy external is used it impacts the device across all time values. 2) I apply an external reference and another oscillator, maybe the default or supplied internal 10Mhz (like a 10811, etc) is now EFC adjusted to phase lock to the external reference. In this way, I would think the phase noise of the device would have been impacted less by the external reference (under the time constant of the PLL or EFC loop. Either way, an oscillator with phase issues used as the external reference is going to have some impact on the device, correct? I’m thinking of in the case where you use a GPSDO that doesn’t have a very good master oscillator. Thanks, Jerry Jerry Hancock je...@hanler.com (415) 215-3779 > On Jan 7, 2018, at 8:05 AM, jimlux <jim...@earthlink.net> wrote: > > On 1/7/18 7:21 AM, Jerry Hancock wrote: >> I’m being a little lazy as I can check the schematics, but in the general >> case, do HP counters, frequency generators, etc, switch to the external >> reference when one is available or discipline the internal oscillator? Are >> there brands of test equipment that generally discipline vs switch? > > > By the each. > > Particularly for newer equipment it can be somewhat of a hybrid - the > Keysight 33622, for instance, seems to have some sort of frequency locked > loop (according to the manual and emails from Keysight). It stays on the > internal reference, but the frequency is adjusted to match the external > reference (whether they adjust the oscillator, or reprogram a DDS, I'm not > sure). > > I've seen test data, though, that seems to imply there's something else going > on - the phase noise is reduced when fed from a quiet external source, and if > it was a simple frequency locked loop, I don't think that would happen. > > >> Third question, again generally, when you discipline an oscillator, what >> impact does this have on the oscillator's phase noise? I assume this third >> question depends on the discipline loop (if I’m using the correct term). >> Thanks >> _______________________________________________ >> 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.
