Thunderbolt GPSDO

My Trimble Thunderbolt GPS Disciplined Oscillator

Design Intent

Here are some photos of a stand-alone monitor for my Thunderbolt GPSDO. I plan to use the 10MHz output as a master reference for all my RF gear. The idea here was to display as much info on the health of the Thunderbolt as a 64x128 LCD would allow.
I think I got most of the important info in there.....

The Thunderbolt has lots of info available, via the trimble "TSIP" binary protocol (see Useful Links). I display some of the more relevant data, given that my objective is not to use this unit as a standard GPS to show my location, but rather as a discilplined oscillator.

Hardware/Firmware Design

This is a really simple project, and is split into 2 halves:

  • The amplification, spliiting and filtering of the 10MHz output.
  • The decoding and display of the Thunderbolt status.
The schematics for the project are shown below. Again, the trusty ATMEGA64 is used for the data decoding and display.

10Mhz Splitter.

Microcontroller and Display.

The 10MHz splitter is really only a series of emitter followers, coupled to some isolating transformers (from ethernet cards).

The ATMEGA64 is used to display data received and decoded from the Thunderbolt. The TSIP packet is first constructed from data received via the UART (interrupt driven). Once a complete packet is received, it is then parsed and relevant data extracted and displayed on the LCD (watch out for Trimble's implimentation of data - it is Little-Endian).
Some extra error-catching and serial time-outs round off the firmware - no user input is required.
My unit was built into an old HP case (I think the case originally held a tracking generator, but by the time I got the unit, it was well and truly for parts only). The simplicity of the hardware allowed me to build on veroboard, making this a quick and cheap project.


The Thunderbolt GPSDO unit.

LCD Display

GPSDO Health displayed on a LCD.

Alarm! Alarm!

Alarm messages on start-up.

What is displayed:

  • Time and Date:
    • GPS or UTC depending upon what the Thunderbolt is decoding.
    • If the Thunderbolt detects that UTC info is unavailable, the "UTC" marker is highlighted.
  • Numerical Fields:
    • 10MHz offset (in parts per billion).
    • DAC voltage.
    • Thunderbolt temperature.
  • Thunderbolt Status:
    • GPS Status.
    • Receiver Status.
    • Discipline Mode.
    • Discipline Activity.
  • Alarms:
    • Up to 5 Alarms are displayed at any one time.
    • Critical Alarms are displayed in preference to Minor Alarms.
    • Critical Alarms cause the "Alarm" marker to be highlighted.

There is no user input, making this a very "minimalist" build. There is however provision to connect the GPSDO to a PC (via RS232). This will allow you to use something like Lady Heather software to log the thunderbolt data or (more importantly) to command the thunderbolt to perform a site survey. This need be performed only once, for a given location.

The finished unit.

Useful Links


1296MHz Activities
26/06/16 Antenna Improvements.
Moon Tracker Ver 2
23/06/16 A new version.
1296MHz Activities
29/09/15 Build a small dish.
26/07/15 Low-noise Preamplifier Design.
1296MHz Activities
19/04/15 Power Amplifier Design.
1296MHz Activities
13/01/15 Design and build a tower for 3m parabolic dish.
30/09/14 LCD monitor for my Thunderbolt GPSDO.
02/08/14 A home-made Noise Figure Meter.
Moon Tracker Update
09/04/14 New rotator and better position feedback sensors added.
1296MHz Antenna
09/02/14 Begin construction of a 1296MHz feed horn for the 3m dish.
1296MHz Activities
28/01/14 After success at 144MHz, operation at 1296MHz is planned.
Moon Tracker Update
11/09/13 Added a Background Sky Temperature calculation into the Moon Tracker.
Moon Tracker Update
28/08/13 Just Added some software limits to rotation of motors.
Roger Beep installed
09/08/13 Added a Roger Beep to my radio.
Andy's Website
06/05/13 Start build of website.


Andy, VK3ANX
Yarra Valley, Australia