[time-nuts] Beginner question - unexpected possible jitter in 1 PPS output of Motorola ONCORE UT+ module
hmurray at megapathdsl.net
Mon May 26 21:58:05 EDT 2014
wb0gaz at yahoo.com said:
> I built a small CMOS divider connected to the UT+ 1 PPS output...
What do you mean by "CMOS"? Old 4000 series parts or HC or ... ?
> Here's the problem: my counts vary significantly (+/- 10000 or more) from
> cycle to cycle, which is much higher than expected based on 50 nS period
> uncertainty of the 1 PPS ...
Do you have a scope?
I'd check the triggering levels. Your counter may be setup to just barely trigger on your CMOS signal. Your CMOS divider may have troubles triggering on the output of the UT+.
One experiment would be to connect the PPS directly to the gate input on your counter. That won't tell you your crystal frequency, but if things work, it should get a consistent count each pulse.
If you have a digital scope, you can trigger on the PPS and look at the PPS in delay by a second mode. (That tells you the accuracy of the crystal in your scope.) If the PPS delayed by a second isn't stable, you know the UT+ is confused.
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