Re: [time-nuts] Reference input on HP counters
On 1/7/18 9:55 AM, Jerry Hancock wrote: 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, I think #1 is the more common traditional approach - the external reference "substitutes" for the internal reference. This leads to all kinds of discussions about "should I use the counter's internal oscillator as the external reference for the spectrum analyzer or vice versa" - since counters usually have good AVAR and drift, but don't worry as much about close in phase noise, while spectrum analyzers are the opposite. #2 is similar to what's going on inside the 33622, I think. The differences in ultimate performance depend on what the various synthesis schemes are, whether loop based with a PLL or direct synthesis with dividers and multipliers. And even if you know the scheme used in a particular piece of gear, the actual behavior is something you basically have to find by experimentation (or asking people who have tried it), since implementations are always "non-ideal". ___ 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] Reference input on HP counters
On the 531xx counters the priority is the external input, the OCXO option, and the (terrible) on board crystal. I seem to remember coming across a menu option for forcing a particular source. ___ 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.
Re: [time-nuts] Reference input on HP counters
Hi > On Jan 7, 2018, at 12:55 PM, Jerry Hancock wrote: > > 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. In the classic HP approach, you have a VCXO at (say) 50 MHz. It is fed by a PLL. The reference to that PLL is either the OCXO in the counter or the external reference input to the device. The loop bandwidth of the PLL is (hopefully) narrow enough that the bulk of the far removed noise is rejected. You always will see the close in ( 1Hz) stuff multiplied up. Since the input to the PLL can be any of a number of frequencies, the gain of the loop (in radians) varies. That impacts the loop bandwidth. Thus saying anything precise about what the cutoff is can be a bit tough ….. Bob > > Thanks, > > Jerry > > > Jerry Hancock > je...@hanler.com > (415) 215-3779 > >> On Jan 7, 2018, at 8:05 AM, jimlux 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. ___ 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.
Re: [time-nuts] Reference input on HP counters
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 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.
Re: [time-nuts] Reference input on HP counters
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.
Re: [time-nuts] Reference input on HP counters
Jerry It depends on the unit and age. There are not rules of thumb from my experiance. Some of the approaches in HP as an example Have switches and demand a specific frequency and level. Some lock an internal reference to any multiple of a reference freq like 5 or 10 MHz. Some are direct some are phased lock. I actually look at each piece of HP gear and see whats going on. Lazy can get you in trouble as I learned. Regards Paul WB8TSL On Sun, Jan 7, 2018 at 10:21 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? > > 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.
Re: [time-nuts] Reference input on HP counters
Hi > On Jan 7, 2018, at 10:21 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? No, not if you are talking about the internal OCXO or TCXO. > Are there brands of test equipment that generally discipline vs switch? Not that I’ve seen. The typical approach is to run a VHF oscillator and lock it to either the internal oscillator or to the external reference input. > > 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). Yes. It also depends on how noisy the reference to the disciplining loop is. The most common case is that the reference is noisy at short tau. There is a tradeoff made in terms of how much noise is introduced vs how well things are disciplined. Bob > > 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] Reference input on HP counters
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? 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.
