Re: [gpsd-users] Enable PPS Echo

[Reto Zbinden ST]

Hello Greg

Nice proposal, I'm going to connect a second GPS receiver to some commodity 
server hardware. Even if this isn't really a measurement, I then can compare 
the embedded board against some standard hardware and check if there's a major 
difference between the two systems.

Regards
Reto

-----Ursprüngliche Nachricht-----
Von: Greg Troxel [mailto:address@hidden 
Gesendet: Mittwoch, 6. April 2016 02:33
An: Reto Zbinden ST
Cc: address@hidden
Betreff: Re: [gpsd-users] Enable PPS Echo


Reto Zbinden ST <address@hidden> writes:

> But if the time is compared to some reliable public stratum 1 servers 
> (e.g. metas.ch), it seems that the local clock is always a few 
> milliseconds behind these servers. I'd like to do some more precise 
> measurement to figure out the latency of the 1PPS signal processing 
> and to adjust the fudge time. According to what I've read, the delay 
> can be measured using an oscilloscope and the PPS echo feature. But I 
> couldn't figure out how the echo function can be activated.

I'll second all the other comments.

Another thing you can do is get a few more models of GPS receiver with PPS, and 
a few more computers, and hook up one GPSr to each computer, and compare them 
across the LAN.  Of course, you can't really conclude that PPS is off from 
this, but if you see really close agreement (sub ms, and maybe even 100 us), 
that's a clue that each of your local GPSr/PPS setups is ok.

Of course, having one GPSr for timing is normal, two not so wierd, three a bit 
funny, and soon after that you're that crazy guy with too many GPS receivers 
that everybody crosses the street to avoid :-)