Time-Nuts Trimble Thunderbolt FAQ

LeapSecond.com

24-May-2008 ; revised 15-Jul-2009

What is this all about?

A large number of Trimble Thunderbolt GPS Disciplined Oscillators (GPSDO) appeared on the surplus market in 2007. We believe it was a byproduct of the ATT/Cingular merger: one of two E911 projects was cancelled and a lot of almost new, never installed telecom gear found itself on the surplus market at bargin prices. [if you have more information on this history please let us know]

How can I order?

See: TAPR Time-Nuts Thunderbolt Group Buy and then TAPR Trimble Thunderbolt Kit.

What GPS antenna do I use?

We think just about any active GPS antenna will work. If you have specific antennas that work (or don't work) let us know.

What power supply is required?

These Thunderbolts require a triple DC power supply: +12 V, +5 V, and -12 V. So this spans everything from an PC power supply to three separate wall-wart power supplies to a highly regulated DC laboratory supply.

What power supply is included?

The first batches of Thunderbolts included a compact switching power supply but the vendor of those surplus supplies ran out. Replacements were too expensive or too noisy or not available in large quantity. Besides there were reports that some of those compact power supplies failed. So a later batch of Thunderbolts was sold without a power supply.

But in 2009 we found a new source of a great power supply for the Thunderbolts and so once again the kits include a universal input triple output power supply. A large quantity of these have been tested for months without a single failure. Moreover, they have less phase noise than the compact power supply of last year.

In addition to the power supply, the hardware to make the DC power connector is included.

How do I make the 6-pin power connector?

This is a standard 6-pin 0.1 inch Molex connector. One connector and 6 crimp pins is included with the order. You actually only need 4 pins, but we included all 6 in case you needed an extra one or two. Double check the color coded power supply wires with a voltmeter.

How do I start the Thunderbolt?

Just plug it in; there's no on/off switch, no reset button, and no software is required to start or operate a Thunderbolt. By default, it will auto-survey and lock to GPS. The 1 PPS and 10 MHz outputs will then be stable.

Where's the documentation?

From the Trimble web site:

Can I monitor the Thunderbolt with my PC?

Trimble offers a nice Windows GUI which connects through a serial port. Use a standard male to female DB9 cable. A null modem adapter is not required. Many parameters can be monitored; some parameters can be changed, either for experimentation or for optimization. The software is free from the Trimble web site:

What are the outputs?

As with most GPSDO, the two BNC outputs are a short rise time UTC-synchronized 1PPS signal and a low noise 10 MHz sinewave RF output.

What level of performance can I expect from a Thunderbolt?

Ignore the plots on the Trimble web site; these Thunderbolts seem to have a high-quality OCXO:

Short-term (ADEV) stability is around 2×10^-12 or better (at one second)
Long-term (MDEV) stability is well below 1×10^-13 (at one day).
The typical GPSDO hump occurs between tau 10 and 1000 seconds, with ADEV climbing to the 1×10^-11 level.

You can find some performance measurements here:

Are these Thunderbolts tested?

They were certainly tested by Trimble as part of their production process. They may have been tested in place as part of the E911 system. It's not clear if they were tested by the telecom salvage firm. However, just to be sure, I tested each one in my home lab.

Specifically, they were powered on for a couple of days and then the free-run (unlocked) performance of the OCXO was checked. In most cases both phase noise and short-term Allan deviation measurements were made. A handful of units were discarded for having unusually weird phase noise or stability . Due to time constaints, I did not test each one under GPS lock conditions.

Who do I contact for further help?

It's probalby best not to bother the main time-nuts mailing list with specific questions about the Thunderbolt group buy -- there are 800 people on the list and they don't all need to know about your particular setup issues. Instead, send email directly to me and I'll answer (and update this FAQ).

Contact info:

I'm at tvb@LeapSecond.com.

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