[time-nuts] Trimble Thunderbolt 10MHz amplitude jitter

Chris Smith chris at evib.net
Mon Apr 19 17:57:02 UTC 2010


I'm new to this list having been recommended to try here for a solution to my problems by Tom Holmes, N8ZM.

I have a 2nd hand Trimble T-bolt which I am trying to use to provide a GPSDO 10MHz reference for my High Performance Software Defined Radio (HPSDR).

I bought the unit from an outlet in California last November but, due to circumstances, have only just got around to using it . 

The first thing I noticed was the Temp pane in TBOLTMON shows -30.8C. Jeff Cook G0AFQ sent me a screen capture of his set-up which shows a temp of 36.7C - more like what I would expect to see. TBOLTMON doesn't show any Critical or Minor alarms and the Lat, Long & Alt are all nominal.

The next thing I checked was the output from the 10MHz osc. The amplitude displays serious jitter of several 10s of mVs. The amplitude jitter seems to be cyclic. There is what appears to be a square-wave impressed on the envelope but at a frequency which is not harmonically related to the base frequency. So the amplitude jitter travels along the 10MHz envelope asynchronously.

The PPS output displays a 10uS pulse at 1 second intervals, so that appears to be working.

I've checked the power rails to the Thunderbolt. All are within a few mV of nominal and clean on a 'scope. So it isn't a problem caused by the power supply.

Has anyone else seen these problems? Can anyone suggest a cure?

I'm happy to approach the supplier of the T-Bolt and see if they will exchange the unit but I thought I'd pick a few brains first.



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