John, Thanks for the headsup. I have three Cs clocks, all of which predate GPS. However, two of the three have expired tubes and I nurse the third by only occasionally switching the beam on. For awhile I was buying used tubes, but now GPS sans SA is so good I don't need the Cs clocks. I do have a Rb oscillator, but I use that primarily to calibrate the frequency synthesizers for my radios.
If I were running a cesium farm I wouldn't want to adjust the clocks either and would rather run a paper timescale. This means that GPS, LORAN-C and simiilar services have to run their own cesia and microsteppers. Once upon a time it was tough to get a really good local UTC lab standard. Before GPS I used LORAN-C; before that I used WWV, CHU, WWVB and Omega. The first NTP servers used the power line, which is synchronized within a few seconds east of the Rockies except Texas. My how things have changed since then. Good cheer. Dave John Ackermann N8UR wrote: > One possibly relevant note is that a lot of standard/metrology labs > don't ever adjust their oscillators, but instead monitor the rate and > deal with that in data reduction. There are a bunch of good reasons > (some of which were recently discussed over on time-nuts) such as > maintaining continuity of data, hysteresis and other bad effects from > making adjustments, etc. > > Modern Cs and Masers have synthesizers that can adjust frequency, > rather than brute-force adjustment of magnetic fields that older units > require. But even in that case, there may be reasons to leave the > thing alone once it's put into service. (There are also nifty devices > like microsteppers that can slew the phase of an input signal at rates > of pico (or femto) seconds per second). > > So the lab may be very happy with those Rbs, even if their raw PPS is > off by a microsecond a week. > > John > ---- > > David L. Mills wrote: > >> Guys, >> >> To be accurate, there are two national timescales in the US, >> UTC(USNO) kept by the US Naval Observatory in Washington, DC, and >> UTC(NIST), kept by the National Institute of Standards and Technology >> in Boulder, CO. I am told the holy grail is to discipline these >> timescales with each other and other standards laboratories within >> one nanosecond. Twenty years ago the grail was one microsecond and >> may still be in some parts of the world. >> >> With an ageing rate of 5e-11, the residual error after one day is 4.3 >> microseconds, somewhat more than would ordinarily be expected of a >> national timescale. Our dedicated public NTP primary servers here >> typically keep within this nominal offset and jitter relative to a >> GPS with PPS. >> >> Other timescales derived from UTC(USNO) include UTC(LORAN) and GPS. >> GPS does not run on UTC and has no leap seconds. It runs on >> International Atomic Time (TAI) with a 5-s constant offset. However, >> what you see in your GPS receiver is UTC as corrected by the GPS >> navigation message. > > _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
