[time-nuts] Some GPS performance plots

Tom Van Baak tvb at leapsecond.com
Wed Nov 3 12:58:27 EST 2004

Your plots are fine. Presumably you're showing how
one can use GPS to check the rate of the Rubidium.
In this case, as in many others, the sawtooth has
little to do with it.

You might try a plot or two using the AVG mode in
Stable32. Tom Clark often used N=300 (5 minutes)
with his 53131 counters. Not only does this clean
up the phase plots nicely but it also does a good
job smoothing the sawtooth without embarking on
a hardware/software project; it becomes what I call
a "mouse project" (all you need to do is click on avg).

One other suggestion, it makes an interesting plot
to show 10 or 20 minutes worth of sawtooth, not
just 20 seconds. The point here is to observe that
there is great variability in the "pitch" of the teeth
of the saw. If you're lucky you can find periods when
the sawtooth is fine, coarse, positive, negative, and
in between like a suspension bridge, or upside down.


> Let's see.  To do that, you'd have to set the logging program up to 
> record the time interval via the GPIB port, and then get the correction 
> value via the serial port, then apply the correction and log the data.
> Well, there's my project for this weekend...
> (Actually, for my real purpose which is measuring the offset of the Rb, 
> it's not worth the effort since I'm averaging over many hours, but it 
> sounds like a good "science fair" project!)
> John

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