The lowest cost solution is a DS chip in combination with a PIC. How ever has any one thought about a fix by going to the source of the problem. The TCXO. Use a DDS with internal multiplier like the AD9851 or AD 9913 and use the sawtooth message from the GRS receiver and change the frequency. An other alternative would be to use the sawtooth word to fine tune a TCXO or any VCXO for that matter. Bert Kehren In a message dated 3/25/2014 7:28:11 A.M. Eastern Daylight Time, phk@phk.freebsd.dk writes: In message <6B362A4D-834A-4733-BED8-FCFEC0CCBA6C@rtty.us>, Bob Camp writes: I should add here, that you _can_ do a little bit better than the sawtooth correction. We know, or at least assume, that the GPS's internal clock is step-less and slowly changing, so if you put a predictive filter on this stuff, it can actually do a reasonable job at estimating which way the rounding of the sawtooth correction went (since it is integral ns). This reduces the random rounding error on the sawtooth correction from +/- 0.5 ns to something like +/- 0.3 ns. Totally not worth it, but a cool and educational project :-) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

On Tue, Mar 25, 2014 at 5:44 AM, <EWKehren@aol.com> wrote: > > The lowest cost solution is a DS chip in combination with a PIC. How ever The lowest cost solution is to do the correct entirely in software. After the measure the phase, simply add the correction. All you need to know is the phase. There is not point in correcting the pulse, you don't need a corrected pulse. What you want is a measurement of the phase. Chris Albertson Redondo Beach, California

> The lowest cost solution is to do the correct entirely in software. > After the measure the phase, simply add the correction. > > All you need to know is the phase. There is not point in correcting > the pulse, you don't need a corrected pulse. What you want is a > measurement of the phase. This depends on the goal. There are two types of GPS timing products. Those which output time & frequency and those which output time only. For time and frequency you design a GPSDO, in which case you have a choice of h/w or s/w sawtooth correction. Most people choose s/w since, as you correctly assume, a GPSDO already includes some sort of phase or time interval measurement circuit along with a microprocessor to do the math. But for a timing only GPS product (e.g., the base models from www.cnssys.com) the goal is just a precise 1PPS output. This class of product tends to use h/w sawtooth correction, since by design there is no TIC or OCXO in the box. There's also a third way to do it -- sawtooth correction provided by PC software tools like Tac32Plus or DSPmon (similar to TBoltmon). In this case the PC reads correction messages from the receiver and measurements from an external TIC and applies the sawtooth correction before writing the composite result to a log file. DSPmon has support for the hp 5334 and 53132. I hope this helps more than it confuses. /tvb