Hi Jim,
On 03/09/2012 10:27 PM, Jim Lux wrote:
I've got a student intern (Undergrad Senior) who's doing a project for
me where he's trying to synchronize (and syntonize) two 1 pps ticks,
generated from different oscillators using some modules in an FPGA.
One oscillator is a run of the mill 66 MHz clock oscillator the other is
a 49.x MHz TCXO. (and, of course, because he's working in a breadboard,
I can swap in a signal generator for either.. I've got a stack of 3325Bs
and 8663s, etc.)
The objective is to get two signals that are 1 pps (or 10 pps) ticks
(each derived from a different oscillator) that align
I'm looking for info to point him to on evaluating the performance of
his implementation.
I've got a HP 5335 (which works quite nicely with a Prologix and John
Miles's tools... thanks John!). I've got oscilloscopes. I've got access
to more exotic stuff if need be (although, since my intern budget is
skinny, stuff I happen to have in the lab, like my uncalibrated 5335, is
better)
For the application, the 5335 will be more than adequate.
I also have a bunch of Wenzel 10 MHz OCXOs sitting around (although for
this, why not use one of the instrument's internal oscillator and
distribute it around)
I do have a hydrogen maser derived reference in the lab, but I'm more
interested in him measuring the two oscillators against each other.
(that is, measuring the performance of the TCXO, by itself, isn't
particularly interesting)
What he needs is some suggestions on things that he can measure that
would be meaningful figures of merit for the application.
He should measure:
- Lock-in transient
- Lock-in time/time-constant
- Lock-in overshot
- Estimate control loop bandwidth and Q-value/resonance
He should then also have a "lock" detector, possibly several lock levels
and illustrate them in the transient waveform.
Then, he should measure the lock-in deviation pattern and measure bias
and RMS noise. Maybe even do a nice ADEV/TDEV set of plots. MTIE plots
is always nice as well.
Showing good control of model parameters and actual performance remains
a good thing. It is usually good to attempt to improve things.
A good exercise is trying to figure out ways to get quick and dead safe
lock-in while also get good in-lock performance. :)
I strongly recommend having a digital scope in parallel with the counter.
He's not doing a PhD dissertation, though.. And he has to be done before
the end of the spring semester. No million second Allan Deviation
measurements.
Should be a good project for him. Keep me posted on the progress.
Cheers,
Magnus
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