3 ms·

Only the expensive ones have the correction capability (e.g. uBlox LEA-M8T) hat tip to tverbeure: https://news.ycombinator.com/item?id=44147523 https://news.yc

Only the expensive ones have the correction capability (e.g. uBlox LEA-M8T) hat tip to tverbeure: https://news.ycombinator.com/item?id=44147523 https://news.ycombinator.com/item?id=44147523 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.)

wowczarek 1y ago
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.
- nullc 1y ago
  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.
  - wowczarek 1y ago
    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.
- RossBencina 1y ago
  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: https://content.u-blox.com/sites/default/files/products/documents/u-blox6_ReceiverDescrProtSpec_%28GPS.G6-SW-10018%29_Public.pdf https://content.u-blox.com/sites/default/files/products/docu... There are cheap LEA-8MT on eBay too, especially if you have a method to pull the module off a scrap board fragment.

wowczarek 1y ago

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.

nullc 1y ago
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.
- wowczarek 1y ago
  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.
RossBencina 1y ago
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: https://content.u-blox.com/sites/default/files/products/documents/u-blox6_ReceiverDescrProtSpec_%28GPS.G6-SW-10018%29_Public.pdf https://content.u-blox.com/sites/default/files/products/docu... There are cheap LEA-8MT on eBay too, especially if you have a method to pull the module off a scrap board fragment.