Hi Chris:
I've done it both ways.
Made up a hardware corrector that used a time delay IC driven by a PIC that corrected the 1 PPS. This is great for
conditioning the 1 PPS into an SRS PSR10 oscillator.
http://www.prc68.com/I/PRS10.shtml
Also wrote some Lab View code that applied the sawtooth correction to the readings from the SR620 TI counter where one
of the inputs was the uncorrected 1 PPS. This works great and saves the expense and complication of the hardware solution.
http://www.prc68.com/I/TandFTE.shtml#SR620
But for the general first case the hardware solution with the delay line is the only way. I think there may be an
exception specifically for the PRS10 in that it may accept a sawtooth correction on the RS-232 input (I seem to remember
that).
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/Brooke4Congress.html
Chris Albertson wrote:
On Sat, Mar 31, 2012 at 7:00 AM, Azelio Boriani
<[email protected]> wrote:
And here:
www.cnssys.com/files/PTTI/PTTI_2006.pdf
Anyway, using a Dallas/Maxim DS1023-100 delay line (and a microprocessor,
of course) you read the @@Hn data from the iLotus M12M and apply the
correction to the delay line. Of course the delay line cannot anticipate
the PPS, so that you have to set a "zero" at the center of the delay line
total span. This fixed delay can, in turn, be nulled out using the M12M
capability to displace its PPS with respect to the UTC. Please, read the
M12M user manual and the DS1023-100 data sheet
It's clear that a fixed offset combined with a variable delay can work
in theory but how much noise (jitter) is added by the delay line? The
uncorrected M12M is so god that I wonder of the delay line correction
is worse than the problem it seek to address.
Maybe a better way is to use the method of NTP. It uses the PPS to
snapshot a counter and stores the value in RAM. It also tracks the
sawtooth functionsand allies the corrected to the value stored in RAM.
So you get the correction but no extra noise for a delay line. But
then in most real-world NTP systems the counter has only uSec
resolution so the sawtooth is mostly moot. But the idea perfectly if
you have a better counter. But only for the one system
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