[time-nuts] Simple GPSDO

Charles P. Steinmetz charles_steinmetz at lavabit.com
Sat Dec 31 02:15:29 EST 2011


I know the thread began with a request for a "simple" DIY GPSDO, and 
this may not be quite as simple as some might like.  However, PPS 
discipline is generally the simplest and most universal scheme from 
the standpoint of interfacing to whatever GPS engine one has 
available.  The PRS10 has a clever system for PPS disclipine, using 
time-tagging for phase detection, that mitigates the usual 
shortcomings of PPS discipline and should be suitable for PIC/FPGA 
implementation.

As implemented by SRS, the discipline parameters are more than 
sufficiently adjustable for any need.  For a homebrew version, the 
VCO would be the quartz VCXO or Rb of your choice.  The pre-filter 
(which is selectable in the PRS10) would be a great help in dealing 
with the jitter in a GPS PPS signal.  PPS locking is discussed at pp. 
14-18 of the 2003 and 2005 manuals.  (The manuals and Rev. H 
schematic are readily available on the web.)

Best regards,

Charles


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