Okay, sounds like I completely misinterpreted the clues in the manual. I'll look forward to seeing what you come up with. Ed On 2017-02-02 11:00 AM, Magnus Danielson <magnus@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