Hi David,
I just finished reading your Sure board web page. That's a really good
write up. I now understand how you're getting the PPS signal. Could
you possibly share the rev level of the board, since, if they change the
design, you patch instructions may not work any more? Some boards don't
have a rev level.
I didn't make a note of the rev levels. Just check that the inverter and
TTL-RS232 gate are spare.
As suggested by Brent Gordon's post, and confirmed in the manual for the
Trimble Copernicus II, I have switched my GPS to output only the GPZDA
sentence and changed the NMEA driver to respond to that. I don't think
the GPZDA sentence has any position information, so it's length should
be very consistent. Whatever the reason, the results are amazing.
Although I've only been running this way for 8 hours, my peak offsets
are now in the +/- 6 ms range. Of course, we'll have to see if the
system continues this way, or if my GPS goes phycho again. This is
twice the level of performance and accuracy than I had before.
Yes, this is excellent news.
Now, I will probably try some PPS stuff, just for intellectual reasons
and just because it would be really cool to see that chart drop under 2
or 1 ms. However, for my simple purpose of just keeping all my PC
clocks right to the second, if I can keep this thing under 10 ms of
error, I'm pretty happy with it. And this is still USB only.
Assuming it's possible to program the Sure board for GPZDA, it would be
interesting to see if doing that affects the performance you're seeing.
Of course, if you're using PPS, the specific content of the NMEA
sentence may not matter as much.
Sincerely,
Ron
From the Sure board you would likely get best results with the PPS line
tied to the DCD pin on a real serial port, and that's what I'm doing.
Cheers,
David
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