You may remember my rant a few weeks ago regarding the 10 MHz output of the Navsync CW12 GPS receiver. The issue was that it was, by design, slightly off frequency. Further testing showed that the offset was also temperature-dependent. Although this doesn't affect its usability for it's intended applications, the 10 MHz output wasn't appropriate for typical Time-Nuts applications.
Connor-Winfield (Navsync's parent company) contacted me and offered a firmware load that turns the CW12 into a CW12-wi. The 10 MHz output changes from a frequency-locked-loop with an offset to a phase-locked- loop with no offset. This load also replaces both 8-channel and 12-Channel OnCore receivers. This isn't a custom Time-Nuts version. It was developed for a particular customer and just happens to resolve the current issue. If you have the NMEA version of the CW12, you can still apply this firmware, but this load emulates the Motorola binary commands only. You will lose all NMEA capabilities and messages. Probably the biggest thing you'll lose is the ability to change the frequency of the 10 MHz output. I am pleased to report that this firmware has resolved the frequency offset issue. I tested both the 1 PPS and 10 MHz outputs and found no drift, just the random wander typical of any GPS receiver. The jitter is about the same as I measured previously. Overlapping Allan Deviation is comparable to other GPS receivers. e.g. http://www.leapsecond.com/pages/3gps/gps-adev-mdev.gif . Testing the 10 MHz output with an HP 5372A Time Interval Analyzer in Histogram Time Interval mode showed that the algorithm has been completely changed. Measuring the period of 50M cycles shows two normal distributions, one centered at 94.0 ns (~20M readings) and the other at 104.4 ns (~30M readings). Apparently, this load 'brackets' the 100 ns point by sending short and long cycles on an almost one-to-one basis that average to 100ns. See http://www.febo.com/pipermail/time-nuts/2011-February/054307.html for similar tests that I did on the existing firmware. Conner-Winfield has asked me not to distribute the software publicly so if you have a CW12 and want the new load, please contact me off-list and I will send you a link to the file. It includes the firmware, flash program, instructions on how to perform the upgrade, and a note on a WinOnCore incompatibility and work-around. The upgrade requires soldering a zero ohm resistor or a piece of wire onto the CW12. If anyone wants to buy a new CW12-wi, I've been told that you can order it directly from Connor-Winfield. I don't have any pricing information. I would like to thank Conner-Winfield for making this firmware available to the Time-Nuts community and I would like to apologize for any offence caused by my rant. Ed _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
