[time-nuts] New Subscriber, DIY GPSDO project (yes, another one)

[Matthias Welwarsky]

On Sonntag, 8. März 2020 02:08:25 CET Bob kb8tq wrote:
> Hi
> 
> Backing up a bit …. the objective is not to minimize overshoot or
> keep the loop from oscillating. The issue here is optimizing the noise
> output of the combination of GPS + OCXO when combined via
> the control loop. It’s a very different objective ….

Absolutely. The GPS will introduce a ton of noise and the objective for the 
control loop is mainly to keep the influence of this noise away from the GPSDO 
output for small tau. You want the GPS only have an influence for large tau, 
ideally only countering the aging of the LO.

> 
> Bob
> 
> > On Mar 7, 2020, at 8:01 PM, Bill Hawkins <bill.iaxs at pobox.com> wrote:
> > 
> > Try https://en.wikipedia.org/wiki/PID_controller
> > 
> > If that doesn't help, what we used to do for industrial process
> > controllers was to set Reset time to the largest value and Derivative to
> > zero (to disable them) and then increasethe gain until the loop
> > oscillated when you made a step change to the setpoint, then you used 70%
> > of that value for gain. The period of oscillation told you how to do
> > Reset, but I don't remember that. Conservative settings were used because
> > control valves were not linear. Heaters are generally linear.
> > 
> > Bill Hawkins, whose memory isn't what it used to be.
> > 
> > On Sat, Mar 7, 2020, at 5:04 PM, Hal Murray wrote:
> >> kb8tq at n1k.org said:
> >>> As far as I know there is no “closed form” solution to tuning a GPSDO.
> >>> It is very much a measure / tweak / measure / tweak sort of thing.
> >> 
> >> I've seen a recipe for tuning a PID controller. That was ages ago. I
> >> wonder
> >> where.
> >> 
> >> The key idea was that you needed to be able to poke the system and see
> >> how it responded.
> >> 
> >> Google for >tune PID< gets several hits that might be worth
> >> investigating.
> > 
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