[time-nuts] Thunderbolt v Active Hydrogen Maser

jim77742 at gmail.com jim77742 at gmail.com
Tue Aug 5 05:55:27 EDT 2008


So why did the Totally Accurate Clock show the same pattern?

On 05/08/2008, Rob Kimberley <rk at timing-consultants.com> wrote:
> I'm pretty certain that this due to position error. You state that you have
> a 5m error in position. 5m equates to approximately 15nS.
>
> Having seen similar results before from positional errors it would be good
> idea to let the unit self survey and then run the tests again.
>
> Rob Kimberley
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Jim Palfreyman
> Sent: 04 August 2008 10:47
> To: time-nuts at febo.com
> Subject: [time-nuts] Thunderbolt v Active Hydrogen Maser
>
> 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
> Date.
>
> 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?
>
> Regards,
>
> Jim
>
>
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