[time-nuts] FW: Question about the PLL of Trimble Thunderbold

Ferran Valdés vantta at hotmail.com
Mon Oct 29 02:38:03 EDT 2018

Thanks everybody for your answers.

@ Bob kb8tq

Due to a development time constraint, I am looking for a board which has all the implemented hardware In order to have a good starting point. My aim is to let the oscillator to be disciplined by the GPS in normal operation, and at a given moment, an algorithm to take over the adjusting process without upsetting the PLL. My idea is to develop the control loop which will be able to synchronize one oscillator to another.

@ ew

A 1 PPS will be exchanged in between nodes (each node would have a GPSDO).

@ Tom Van Baak

Yes, a GPSDO is already self adjusting, but for my project, I would like to either use a GPS or to synchronize one node’s oscillator on another.

The synchronization goal is in the order of ps level.

@ Mark Sims

I have just taken a brief look at Lady Heater. I will go through the manual and get back to it. But what this program does is similar to what I am intending to do, so that’s quite nice to know that the Trimble Thunderbolt is a suitable board !

I am searching for the time interval, but I have not seen the parameter yet.

This is the command to set the DAC value --> 0x8E-A0  | Set/Request DAC values  | 0x8F-A0

Within the Report Packet 0x8F-AC, the bytes 16-19 indicate “Estimate of UTC/GPS offset”, is this the time difference ?

I have seen that on eBay, there are listed some GPSDO modules, which claim to have a “trimble” or “symmetricon” GPSDO inside, and they provide a hardware platform to get access to the GPSDO parameters, however, it depends on the board which is mounted inside if the adjustment loop can be externally governed. Anybody got any experience with any of those boards?

Kind regards,


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