[time-nuts] Thunderbolt v Active Hydrogen Maser
rk at timing-consultants.com
Tue Aug 5 06:11:45 EDT 2008
Good point. How was the position of the so called "Totally Accurate Clock"
obtained. Strange name though - no such thing as a totally accurate clock...
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of jim77742 at gmail.com
Sent: 05 August 2008 10:55
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Thunderbolt v Active Hydrogen Maser
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
> 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?
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