[time-nuts] TruePosition GPSDO performance (Packrat version)

Mark Sims holrum at hotmail.com
Sat May 13 14:23:33 EDT 2017

I got in one of the older style Trueposition GPSDOs from China.  This is the board shown in the "Packrat" documentation.  It uses a Bliley OCXO instead of the CTS one on the newer board.

Other than the connector differences, the only significant hardware difference seems to be the temperature sensor.  This board has a 0.01C resolution.  The newer board has 0.03C resolution.   The software command set seems to be the same.   Both output the same data.  The older board tracks WAAS satellites like the newer board.

The Bliley OCXO seems to be slightly better.  It has same response to a cold spray attack,  maybe a little less sensitive.  The older board seems to have better holdover characteristics...  there were only two brief "soft" holdovers overnight (the actual status messages said they were wait states, so  probably not real holdovers.  There was no PPS disturbance)  The ADEVs on the older unit are better than the newer board by around 30%.

Attached is the ADEV / PPS plot from a TAPR TICC.
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