[time-nuts] Some GPS performance plots

Brooke Clarke brooke at pacific.net
Wed Nov 3 12:46:32 EST 2004

Hi John:

Years ago I tested the Oncore VP+ and found the sawtooth had glitches.  
But I did make the correction two ways.
The software approach was to measure the time interval via HP-IB and the 
saw tooth via RS-232, then use the PC to apply the sawtooth prior to 
plotting or recording the data.

The hardware approach was to use a PIC to read the sawtooth value and 
then program a digital delay chip placed in line with the 1 PPS output.  
As far as I can remember the chips came with 1 or 1/2 nanosecond steps 
and by starting half way you could get positive or negative sawtooth 

But they both caused poorer results with the VP+ because there was a bug 
in the sawtooth data.

Have Fun,

Brooke Clarke, N6GCE

w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml

John R. Ackermann N8UR wrote:

> Nothing sexy here, but in response to some serious confusion on the 
> NTP mailing list, I put together some plots of the 1pps output from a 
> Motorola M12+ Timing Oncore versus an Rb standard.  It may be helpful 
> if you want to point people to info about GPS timing capabilities.
> http://www.febo.com/time-freq/gps/performance/index.html
> (Some folks on comp.protocols.ntp were busy lawyering the Motorola 
> manual and getting really screwed up about the accuracy -- or lack 
> thereof -- of the 1pps signal.)
> John
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> time-nuts at febo.com
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