[time-nuts] Re: General discussion of PID algorithms applied to GPSDO control loops (continued 1)

[Skip Withrow]

One of the things that cannot be ignored are the statements made in
item #10 regarding the DAC and OCXO EFC.  If the DAC is 16 bits that
is 2^16=65,536 steps.  If the DAC outputs 0-4 volts that is 61uV/step.

Now you have to take this number and multiply it by your OCXO
sensitivity (not given), and you have the minimum frequency step that
can be made.

This is the best that you can ever do.  So, your TIC/1pps resolution
does not need to be any better than this.  Waiting a long time to get
higher resolution may (probably) buys you nothing.

This is where all the magic comes in - higher resolution DACs, more
stable oscillators, more stable GPS PPS, etc.

To a first order, overlaying the line from item #6 with the ADEV of
the oscillator used and setting the loop time constant at the
crossover tau works pretty good.

As has been said many times, if it was easy everybody would be doing it.

Regards,
Skip Withrow