[time-nuts] Lost Calibration on CNT-81/PM-6681

Ed Palmer ed_palmer at sasktel.net
Thu Feb 2 13:08:23 EST 2017

Okay, sounds like I completely misinterpreted the clues in the manual.  
I'll look forward to seeing what you come up with.


On 2017-02-02 11:00 AM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> Hi Ed,
> First of all, don't be fooled to think it is "calibrated", not yet.
> What I've done so far is just starting to make my ways into the GPIB
> commands to make it do the right things.
> I've not even attempted to do the right thing in terms of actual
> calibration, but trying to make sure that I can get it to do the
> necessary stuff.
> Anyway, one trick being used is to use a locked offset oscillator, that
> effectively sweeps all phase relationships over the 10 MHz cycle stable,
> predictably and evenly. This way it sweeps over all the phase
> relationships to the locked 100 MHz oscillator and the 10 ns time error
> window that is then expanded 400 times in the interpolator before being
> counted in the 100 MHz clock. The scaling of this is done with an
> internal reference pulse. The internal reference pulse needs to be
> calibrated with external software, and once established it is put into
> the PUD command and used in the internal self-calibration routines.
> So, 4.05 ns or 4.29 ns is really a property of that hardware.
> I have not attempted to do the routine to establish the calibration
> pulse length yet, I'm trying to clear the way before I get there.
> Hence, I have not yet cared about actual precision yet.
> Cheers,
> Magnus

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