In message <459054DC.8030701@xtra.co.nz>, Dr Bruce Griffiths writes: >> A quantum of 1ns is not a concern if the attack point for the PLL >> is on the order of hours. >> >This statement is only true when one is disciplining or monitoring >relatively with sufficiently large frequency and/or phase instabilities. >When one wishes to discipline an Oscilloquartz 8607 OCXO for example >every nanosecond or fraction thereof matters. As far as I can see on TVB's site, the 8607 is about 5e-13@1000 sec, so 1ns/1h sounds perfectly good to me. >Its not the coherence of the sawtooth but the coherence between the >oscillator clocking the timer used to position the PPS signal and the >frequency of the PPS signal itself. Yes, those are non-coherent, that is why we need the negative sawtooth in the first place. If they were coherent, we could just have used a formula. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

Poul-Henning Kamp wrote: > In message <459054DC.8030701@xtra.co.nz>, Dr Bruce Griffiths writes: > > >>> A quantum of 1ns is not a concern if the attack point for the PLL >>> is on the order of hours. >>> >>> >> This statement is only true when one is disciplining or monitoring >> relatively with sufficiently large frequency and/or phase instabilities. >> When one wishes to discipline an Oscilloquartz 8607 OCXO for example >> every nanosecond or fraction thereof matters. >> > > As far as I can see on TVB's site, the 8607 is about 5e-13@1000 sec, > so 1ns/1h sounds perfectly good to me. > > Only true when one only considers the data available on Tom's site. Quartzlock have a GPS disciplined BVA OCXO that achieves considerably better stability, admittedly their carrier phase tracking GPS receiver has a resolution of a few picoseconds for an integration time of 1 second. >> Its not the coherence of the sawtooth but the coherence between the >> oscillator clocking the timer used to position the PPS signal and the >> frequency of the PPS signal itself. >> > > Yes, those are non-coherent, that is why we need the negative sawtooth > in the first place. If they were coherent, we could just have > used a formula. > But they are not sufficiently incoherent as hanging bridges and the quasi periodic form of the sawtooth error amply demonstrate. Bruce

In message <45905B32.4000301@xtra.co.nz>, Dr Bruce Griffiths writes: >> >> As far as I can see on TVB's site, the 8607 is about 5e-13@1000 sec, >> so 1ns/1h sounds perfectly good to me. >> >Only true when one only considers the data available on Tom's site. >Quartzlock have a GPS disciplined BVA OCXO that achieves considerably >better stability, admittedly their carrier phase tracking GPS receiver >has a resolution of a few picoseconds for an integration time of 1 second. I'm not sure what your point is here... Obviously if you discipline something with an Oncore, you have to choose a PLL timeconstant that is optimum for the oscillator you are using. If your oscillator is very good, the oncore may not be good enough at any timeconstant. But the 1ns resolution of the Oncore is a fact of life and for all the "amateur" stuff we are talking about here, 1ns is plenty fine. >>> Its not the coherence of the sawtooth but the coherence between the >>> oscillator clocking the timer used to position the PPS signal and the >>> frequency of the PPS signal itself. >> >> Yes, those are non-coherent, that is why we need the negative sawtooth >> in the first place. If they were coherent, we could just have >> used a formula. >> >But they are not sufficiently incoherent as hanging bridges and the >quasi periodic form of the sawtooth error amply demonstrate. Your choice of the word "coherence" does not help the discussion here because it implies that the signals are the same frequency, which is not the case. But if you insist on using the word coherence, then at least use it correctly: The hanging bridges happen because the two signals are not coherent. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.