[time-nuts] Jupiter GPS Settings For Best Timing Performance

David Smith david at smithfamily.net.au
Thu Apr 10 07:05:28 EDT 2008

I've been working on the performance of my portable GPSDO (very similar 
to G3RUH design) and have got down to a reasonable level.  Testing 
against an HP3815A, it will remain within better than 1x10^-10 for 
periods of 10-15 mins.

However, there are times when it seems to get a "hit" and it will then 
move up to ± 5x10^-10 before settling down again.  The movement seems to 
follow the time constant of the PLL loop filter, possibly indicating 
that it's coming from the Jupiter GPS?

Reading the Jupiter doco (Zodiac GPS Receiver Family Designer's Guide), 
there seem to be several Zodiac Binary messages that can be used to 
alter the GPS's performance (e.g. Satellite Elevation Mask Control).  I 
already have a processor talking to the GPS card and displaying 
position, time, gridsquare, status etc.  It would be a simple matter to 
have it tweak the parameters as required.

Does anyone have any experience with this?

David Smith

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