[time-nuts] GPSDO simulation tool

Don Latham djl at montana.com
Sun Mar 23 12:08:40 EDT 2014

I agree..  Had a maybe weird thought.   Computing power is now a trivial part
of the "problem", in that a Ras.Pi can be put to the task for $35 or so. In
that case, PIDdling with time constants and such in a feedback loop with phase
difference as the error signal is easily done, either in simulation, or for
real, as you point out. So, since ADEV or one of its brothers is the measure
of success of PIDdling, shouldn't the ADEV or brethren be in some way the
error signal for the whole?  For example, how about a TCGPSDO? put the whole
thing in a first-order thermal enclosure, with power-over-ethernet being the
only  external wiring?
Hope I'm at least making at least logical sense

Tom Van Baak
> Hi Don,
> Yes, easy! And that's exactly the idea -- to take real inputs (or borrowed
> copies of real inputs), and a real software algorithm, and measure the virtual
> output to see how well your algorithm and tunable parameters work. Tweak
> parameters. Evolve the algorithm. Simmer until well done.
> Theoretically, after one builds the real GPSDO, using the same code or at
> least the same algorithm, the actual performance should nearly perfectly match
> the simulation.
> The difference, at least for me, is that I'd rather play with unix commands
> and C code on a PC, trying things out in a matter of minutes, than spend weeks
> slowly trying different things with a real GPSDO (which I've also done). In
> addition, I think gpsim1 makes a useful, almost interactive, teaching tool.
> Now, no simulation is perfect. But oscillators, dividers, 1PPS comparators,
> and DACs are not really that complicated. You are probably guessing that I'm
> working on gpsim2 which will allow simulation of phase and frequency jumps,
> varying GPS reception, power-up, cold-boot, warm-boot, holdover, thermal or
> mechanical shocks to the instrument, and other events that I see in real life.
> But let's let gpsim1 run its coarse before we worry about 2nd order effects.
> I'm very interested in alternative or enhanced algorithms that people come up
> with. The two algorithms now in gpsim1 and default tuning parameters are just
> something I threw together in a few minutes.
> /tvb
> ----- Original Message -----
> From: "Don Latham" <djl at montana.com>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Sent: Saturday, March 22, 2014 8:18 PM
> Subject: Re: [time-nuts] GPSDO simulation tool
> Hi Tom et.al.   Isn't the simulator "easily" convertible to the real thing?
> That is, data inputs should be convertible somehow to data streams from
> physical devices?
> Don
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"The power of accurate observation is commonly called cynicism by those who
have not got it."
 -George Bernard Shaw

Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
Skype: buffler2

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