I have been looking for a PPS GPS for quite some time.
Most of them are expensive and on AliExpress none of them have PPS.
However, after a long search I found one that is really cheap, about 50~60 Euro/USD depending on shipping.
But beware, when they ship to Europe you will probably charged extra import taxes, for me in Belgium that was 41 euro extra.
Anyway, it’s still very cheap.
You can find the device here:
You only need to tell GPSD that the box registers as /dev/ttyUSBx (USB0 in my case).
I use Chrony and configured it like this:
refclock SHM 0 refid NMEA poll 4 precision 1e-3 offset 0.1256 delay 0.2
refclock SHM 1 refid PPS poll 4 precision 1e-9 lock NMEA prefer
When you run it, you can expect this:
MS Name/IP address Stratum Poll Reach LastRx Last sample
#- NMEA 0 4 377 24 +1000us[+1024us] +/- 101ms
#* PPS 0 4 377 22 +264us[ +287us] +/- 22us
Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
NMEA 6 3 80 +16.270 108.450 +2372us 752us
PPS 64 56 1008 +0.006 0.263 +55ns 193us
Reference ID : 50505300 (PPS)
Stratum : 1
Ref time (UTC) : Thu Feb 13 14:33:01 2020
System time : 0.000005683 seconds fast of NTP time
Last offset : -0.000005592 seconds
RMS offset : 0.000012070 seconds
Frequency : 28.518 ppm fast
Residual freq : +0.001 ppm
Skew : 0.323 ppm
Root delay : 0.000000 seconds
Root dispersion : 0.000054 seconds
Update interval : 16.0 seconds
Leap status : Normal
The USB bus is a bit slower then RS232, but hey, it works and works well.
I have been searching for more then a year to find something on USB that is not that expensive.
I believe this is the one.
Also, Steve bought one too, he can give far better details with his programs and charts.