I recently add the ability to Lady Heather to monitor a PPS output and apply
sawtooth correction sto the measured PPS and log the results.
The Venus timing receivers tout a PPS output with +/- 6 nsec PPS jitter and
sawtooth corrections. Alas, the PPS output does not appear to meet this claim.
The latest receivers that I tested were the Venus/Navspark/Sayer timing
receivers that use the Venus GPS timing receiver chip. I was measuring PPS
jitter on the order of -26/+32 nsec, which a +/-6 nsec sawtooth correction
message has little useful effect on. Plotting a histogram of the measured PPS
values shows several humps in the histogram that are spaced 12 nsec apart. It
seems that their PPS generator has some issues deciding just which clock cycle
to trigger on.
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