We are working on a locomotive project using Quectel GNSS LC76G, we need information on the 1-PPS generation.
We have configured 1-PPS to After the first fix ($PAIR752,; here PPSType = 1), but when GPS loses the signal (for test we are disconnecting antenna) the 1-PPS is genrated only for 45 minutes, after 45 minutes there is no 1-PPS signal.
Could you please help us understand this and find a resolution? We need 1-PPS signal generation for a minimum of 1 hour in case the GPS signal is lost.
For GNSS module, it needs to synchronize with satellites, then output PPS signal. In your case, LC76G lost fix for more than 45minutes. During no fix time, PPS error was accumulating. After waited for 45minutes, PPS accuracy is not reliable and module stopped output it.
The best way to restore accurate PPS output is to return to open area.
I have another suggestion: you can set “PPS always output”. After module goes back to open area, it starts synchronze and output accurate PPS. When module goes to no-signal area, it reckons PPS according to RTC clock.