[time-nuts] Sneaky Errors
bill at iaxs.net
Wed Oct 19 23:31:01 UTC 2011
Seems to me that 200 ns is 720 degrees of phase error, which is a lot.
A person handy with logic circuits could build a simple phase detector
with a flip-flop and an RC filter with a tenth second time constant.
An analog circuit could detect 360 degree rollover and set off alarm
bells. Note that you still have the two-watch problem.
Two equal divider chips ahead of the flip-flop could allow larger errors
before rollover. The error may reverse itself and run the phase error down,
and then reverse again as the two ovens cycle at different rates. This
would be normal behavior, unworthy of an alarm.
An additional challenge would be to build logic to select the oscillator
output to be distributed, then compare the output to the output of three
oscillators in three phase detectors. The device that had phase rollover
would put itself in standby, alarm, and leave you with the two watch
Perfection demands many oscillators with a voting system. Long winter nights
could be spent solving these problems. I'm too old for that stuff.
(I also post the most recent ideas first, so as not to reread old ideas.)
From: David VanHorn
Sent: Wednesday, October 19, 2011 5:58 PM
Magnus said (note the attribution),
"Steadily increasing phase error is to let there be a frequency error.
Frequency is the derivate of phase, so it comes with the territory.
So a 200 ns per second phase drift would provide a frequency error of 2
Hz on your 10 MHz. Can't have one without the other."
I understand, I'm just saying that if the absolute phase is wandering a bit
over tens of seconds, it's NOT an issue.
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