NTP Server: GPS

[Patrick M. Hausen]

I clamped a small sheet of metal to the book shelf that is standing right next to the window in my office and attached the magnetic indoor antenna to that. So it's sitting perpendicular to the window about centred in window height and a foot or so removed from the wall. "looking out" to the west and up.

Code Select Expand

                        window                                                                   
──────────────────┌─────────────────┐─────────────────────────────────────────────────────────────
                  └─────────────────┘  ┌─────────────────────────────────────────────────────────┐
                                       │                                                         │
                                      ┌┤                        bookshelf                        │
                              antenna └┴─────────────────────────────────────────────────────────┘

See attachment for the GPS status as shown by the device's UI. No precise idea about the sync time - couple of minutes.

[pfry]

[...]
@pfry: you can not trigger on NMEA, because PPS is its own line on the serial interface and only that line carries that signal.
[...]

Implementation dependent. Current RS-232 and USB implementations may have issues, but the old discrete UARTs could be configured to interrupt immediately on any signal. In addition, GPS receiver implementation will likely not support precise timing of NMEA data, but some old ('90s) units did have this option. I recall one in particular with its PPS optionally connected to DCD and normally disabled, as its normal RS-422 didn't have control lines. I'll have to plug in my old Ultralink WWV clock and see how bad it is now, as it uses a similar method (time delivered on the second, with PPS disconnected). It used to be quite accurate back in the day.

[bimbar]

[...]
@pfry: you can not trigger on NMEA, because PPS is its own line on the serial interface and only that line carries that signal.
[...]

Implementation dependent. Current RS-232 and USB implementations may have issues, but the old discrete UARTs could be configured to interrupt immediately on any signal. In addition, GPS receiver implementation will likely not support precise timing of NMEA data, but some old ('90s) units did have this option. I recall one in particular with its PPS optionally connected to DCD and normally disabled, as its normal RS-422 didn't have control lines. I'll have to plug in my old Ultralink WWV clock and see how bad it is now, as it uses a similar method (time delivered on the second, with PPS disconnected). It used to be quite accurate back in the day.

That is also what I have seen, that PPS is connected to DCD, but I do not know of any way to do precise NMEA timing without PPS.

[Greg_E]

I use double sided foam tape and stick the antennae to a south facing window. With the above devices, this is currently what I get on a snowy cloudy day. If the option was easier, I would put up an external antenna, I'm on the ground floor of a three story concrete and steel building, the north is completely occluded, east is partially occluded, west is decent, and south completely clear.

These do have PPS output on the back, so I'm guessing fairly accurate. Matches the time from my phone at any rate which is good enough for me right now.