GPS timing modules should have a sawtooth correction value that will tell you the error between the upcoming pulse and GPS time. The issue is that PPS pulse has to be aligned to the receiver's clock. Using that will remove the main source of jitter.
Applying sawtooth correction will remove _some_ of the jitter but at the time server level, not network level, and quantisation error is not the main source of jitter here (I'm talking long time constants) - Packet Delay Variation (PDV) and internal time comparisons are. Plus, any decent loop should average the sawtooth and transform it into fluctuations slow enough that they will not have that much effect on what is being measured in the blog post - the output of the time server looks nothing like the raw 1PPS input, at least in the short term it doesn't. Of course sawtooth should be removed and let's hope his time servers do it, especially the RPi ones.
You can't really, depending on their relative phases and the resulting aliasing products the average of the sawtooth error can still have an arbitrary offset which last for an arbitrarily long time.
> that they will not have that much effect
okay fine for some definition of 'not much' that's true. But failing to account for it can result in a bigger error than many people expect-- and in an annoying way, since when you test it might be in a state where it is averaging out okay but then later shift into a state where it's producing an offset that doesn't average out.
Assuming your receiver outputs the correction it's pretty easy to handle, so long as you know it's a thing.
Aligning the PPS pulse with an asynchronous local clock is going to require a very large number of measurements, or a high resolution timer (e.g. a time to digital converter, TDOA chip, etc. there are a few options.)
To an extent. You can get previous generation GNSS receivers with sawtooth correction for cheap, eBay is full of those, say an old Trimble Resolution whatever, and lots of LEA-6T carrier boards going for $20-range, and bare modules for less. I would trust those carrier boards more though, less chance of getting a fake module.
Great, thanks. For anyone following along at home, LEA-6T reports the time pulse error in picoseconds in the TIM-TP message. See "11 Timepulse" on page 26, and/or search for "TIM-TP" in the product spec:
The timing receivers often have other advantages beyond just sawtooth, including stuff like being able to produce a time pulse with a single working satellite in view once their position is learned.
Should have clarified: previous generation timing receivers. Yes, self-survey + stationary mode + O/D mode where you can track a single SV and such, are essential for stable time sync, not just sawtooth.
There is an exception re. sawtooth, but only a recent one: the Furuno GT-100, priced between the ZED-F9T and the Mosaic-T, has 200 ps clock resolution and doesn't even provide a quantisation error output.
