Peter
PV) However, I think it would be interesting to at least see the relative
differences for one location.
The relative difference can be seen in the Green Dac plot, which shows
the total PP noise at 50 Sec and slower.
The Dac is scaled to 1e-11 per division, for RMS or ADEV, divide PP by about
5.
As you pointed out the Tbolt and LH can NOT do 1 sec noise directly without
an external reference,
BUT by looking at the excess nose that is applied to the DAC, you can see
what is happening at one sec, or 10 or 100.
Ideally The Dac should not be forced to move at a freq below the TC setting,
If it does that is added noise.
By the way,
To force a similar sort of 50 ns sawtooth phase error waveform when using an
external reference,
Use the Osc phase setting to invert the phase of the Tbolt OSC sync timing.
PV) Is the oscillator in the Leica significantly worse than that in out
Thunderbolts, or could we also benefit from a time-constant of longer than
1000 seconds?
I know little about anything except Tbolts
but If you show me a couple of good plots, with and without GPS control, I
could probable answer that.
PV) I will try to find a quiet rubidium
Depending on what errors you are most concerned with, Phase short term
or long term , Low tau ADV or High Tau ADV, (or hold over, yek)
May not even be necessary for it to be a "low noise quiet one"
Have fun
ws (in central California)
***********----- Original Message -----
From: "Peter Vince" <pvi...@theiet.org>
To: "WarrenS" <warrensjmail-...@yahoo.com>; "Discussion of precise time and
frequency measurement" <time-nuts@febo.com>
Sent: Wednesday, December 16, 2009 4:54 AM
Subject: Re: [time-nuts] Tbolt Damping setting
Good points, and You got 4 1/2 out of five correct, Not bad at all.
Ha ha - thank you teacher!
Fairy nuff, yes, your plots show the long-term effects. I would like
to know what the best time-constant is to use. I appreciate that
everyone's will be different, depending on individual characteristics
of the Thunderbolts, and also (perhaps more importantly) the aerial
and its position. However, I think it would be interesting to at
least see the relative differences for one location. I recently
learnt that our national mapping organisation (The Ordnance Survey)
average the results from their L1/L2 Leica 1200 system receivers, for
two hours. Is the oscillator in the Leica significantly worse than
that in out Thunderbolts, or could we also benefit from a
time-constant of longer than 1000 seconds?
I will try to find a quiet rubidium, and do some comparisons against
that - the results should, at least, be valid out to a few thousand
seconds. I also plan to try reducing the signal level threshold (from
the current 4AMU) as recently suggested, and try to see some
quantifiable results.
TTFN,
Peter Vince (G8ZZR, London, England)
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