ntpsec is ignoring PPS

Hal Murray halmurray at sonic.net
Wed Dec 1 23:26:32 UTC 2021

folkert said:
> PPS(0) is a regular garmin lvc18, while PPS(1) is a GPS disciplined
> oscillator, this one: http://www.leobodnar.com/shop/index.php?main_page=produc
> t_info&cPath=107&products_id=234 The GPSDO emits a 10MHz signal that is
> divided to 1PPS using a "picdiv" (http://www.leapsecond.com/pic/picdiv.htm ).
> As suggested by the website, a 100nF capacitor has been connected.

I think you are missing the key step.

The PPS from a GPS unit is carefully setup (by the GPS box) to start at the 
start of a UTC second.

The picdev doesn't know anything about UTC.  Its pulses will be 1 second apart 
(if your 10 MHz is accurate), but they will start at an arbitary time relative 
to the start of a UTC second.

> So that works but PPS(1) shows an 'x' before it. I see a rather
> (surprisingly) large offset but jitter is always low (less than 0.02).

Basically, that GPSDO and a picdev isn't the right tool for what you are 
trying to do.

If you power cycle your picdev you will get a new offset.

Does the picdev have a way to move the PPS around so you can adjust the 
PPS-UTC offset? That would need a good PPS to compare it to  If nothing else, 
you can short out the clock input.

Plan B is to fudge the offset in the config file.

How good is your antenna?  The picdev output will probably drift a bit when 
the GPSDO looses contact with GPS.

These are my opinions.  I hate spam.

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