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

ernieperes at aol.com ernieperes at aol.com
Thu Apr 10 07:46:17 EDT 2008

Hi David,

my experience is that if you use "analog" control after PLL then it 
comes from the birds how the JUPITER is
handling the data-streams. The digital control has the advantage in 
this respect.

Rgds Ernie.

-----Original Message-----
From: David Smith <david at smithfamily.net.au>
To: time-nuts at febo.com
Sent: Thu, 10 Apr 2008 1:05 pm
Subject: [time-nuts] Jupiter GPS Settings For Best Timing Performance

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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