[time-nuts] Thunderbolt v Active Hydrogen Maser

Jim Palfreyman jim77742 at gmail.com
Mon Aug 4 05:47:16 EDT 2008

Hi folks,

I took my recently acquired Thunderbolt, along with my 5370B, to the
observatory on the weekend and plotted its residual against the NR Active
Hydrogen Maser. See the attached graph (ignore the "line of best fit"
heading - 0.00 was simply the starting point).

Note that I didn't let the Thunderbolt do a survey, I simply plugged in the
local GPS coordinates which I later verified were about 5m to the east of
the actual Thunderbolt antenna.

The y axis is residual in nanoseconds and the x axis is Modified Julian

I find the residuals fascinating. Note the identical repeating residuals in
a 24 hour cycle.

Is this due to thermal or constellation issues?

The local GPS (not a GPSDO but an early version Totally Accurate Clock)
showed a roughly (very roughly) similar pattern when averaged with 5 minute
averages to hide the awful 100nsec sawtooth.

The observatory is air conditioned (but with poor insulation) and has many
devices constantly running. I doubt it is thermal, however the low point is
at 6:30am in the morning, just before I arrived.

Can anyone provide comment on this pattern?


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