[time-nuts] True Position GPSDP + Rb X72

Mark Sims holrum at hotmail.com
Thu Sep 21 15:58:29 EDT 2017

X72 support in Lady Heather is a new feature not in the current v5.0 release.   If you are running under Linux or can build the v5.0 Windows code, I can send you the latest version tp compile.

The X72 has a DDS synthesizer on it that lets you vary the output freq in steps of 2.03E-12 parts.  My X72's are off around 6E-10 from nominal (DDS word set to 0).   

Besides the disciplining code Heather also has a calibration routine that can adjust the DDS to on frequency.  It works by connecting a 1PPS  input to the X72, setting the DDS word to 0, collecting data for a specified time interval (like one hour).  It then calculates how far the 1PPS in and 1PPS out are apart using the X72's built in 16.67 ns res TIC.  From that it determines the DDS word needed to cancel the 1PPS drift.   

The X72 has a command for saving something in EEPROM (they never say what it actually saves).  I don't know if the DDS word is part of what it saves...  I think different firmware versions save different things.

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