Ah, Magnus, source of so much solid and useful information, I don't see a time loop as valid.
Frequency, yes, social time, no. A clock (purveyor of time) consists of an oscillator and a counter. In olden times the oscillator was a pendulum and the counter was a set of gears driven by the tick-tock of the escapement. Today we have electronic local oscillators providing one pulse per second (or whatever is needed) to electronic counters and displays. As an old timer, I prefer neon Nixie tubes. The problem we struggle to solve is to relate our local oscillator to some widely recognized standard frequency, preferably derived from an inordinately expensive generator based on the bouncing of atoms under controlled conditions. The very best way to transfer the standard (not "At the tone, the time is ...") is to use an electronic phase comparator, error amplifier, and filter time constant that will cause the local oscillator to track the standard *frequency* usually propagated by GPS. The remaining problem is to get the counter to agree with our preferred version of time display (UTC, TAI, etc.). If the display electronics permit adjustments such as adding a second at a predetermined time, or adjusting by an hour for summer or winter time, then our needs for social time can be satisfied. I don't see the need to yank the oscillator around for social time with a "time loop." Best regards, Bill Hawkins P.S. We're moving to a life care community that has no room for a time lab. The Junk Genius truck arrives at 10300 Colorado Road, Bloomington, MN 55438, at 11 AM on 1 September. If you can get here before that you can have anything you see. There are only antiques, except possibly the HP 3335A synthesizers and Racal Dana 1882 counters. I've tried to sell a few times but have had no takers. I won't ship (no time) but you can hire someone to pick it up. -----Original Message----- From: time-nuts [mailto:[email protected]] On Behalf Of Magnus Danielson Sent: Saturday, August 29, 2015 9:47 PM To: Discussion of precise time and frequency measurement Cc: [email protected] Subject: Re: [time-nuts] FLL errors Hi, On 08/29/2015 11:24 AM, Neville Michie wrote: > > A PLL locks on to the nearest cycle, > is a Time Locked Loop different? Yes and now. In a signal conveying time, rather than letting a rising edge denote "0 degrees of phase" you have some even time measure occuring, of some known nominal rate. You know what "time" it was on the time-scale, so that you know how much your local replica time-scale is off when compared. This time difference does go beyond the nearest cycle, but typically for locked situations is the nearest cycle. Don't ask how I know, I just know. > If the decoded time from a GPS system is used discipline an oscillator > then leap seconds would have to have a frequency transient to maintain > lock. No, as GPS time in itself does not have leap-seconds, it's nominally the TAI time-scale offset. GPS signal conveys the difference between GPS time and UTC, and thuse the UTC can be conveyed. > If you use the output to say drive a radio telescope monitoring a > distant object you would want Earth's rotation to be phase or sidereal > Time locked. I realise that for such a task far more complex > computation would be required. > So is a time locked loop a valid concept? Yes, whenever the enumeration of cycles to some time-scale is relevant. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
