[time-nuts] Z3801A with other GPS receiver

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri May 18 18:05:38 EDT 2007

Brooke Clarke wrote:
> Hi Didier:
> I seem to remember that one or more of the HP boxes that used the 6/8 channel 
> Motorola GPS receivers used a secret method of making use of the sawtooth error 
> information.  Some trick was needed because there was a bug that caused the 
> sawtooth to be wrong every now and then and it always was wrong in the same 
> polarity.  Therefore you could not average using the sawtooth.  Most 
> applications just ignored the sawtooth output and averaged.
> But if the Z3801 is using the sawtooth, and you replace the receiver with 
> another model, then there will be a problem.  A fix would be if someone would 
> come clean and tell us how HP got around the sawtooth bug in detail, then you 
> could take the output from an M12+T and recreate a data stream that would look 
> just like the 6/8 channel unit including the buggy sawtooth byte.
> Have Fun,
> Brooke Clarke
> http://www.PRC68.com
> http://www.precisionclock.com

Of course one potential problem with using an M12 or later timing 
receiver is that it is perhaps conceivable that the carrier phase data 
available from the earlier receivers (but not from the M12 and its 
successors) may have been used to correct/detect sawtooth correction 
errors. The only way to settle this is in fact to log and analyse the 
"conversation" with the timing receiver.


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