[time-nuts] Measuring ADEV using TBolt-Tic tester
warrensjmail-one at yahoo.com
Fri Oct 7 17:00:42 UTC 2011
Few TIC instruments can be used to measure 1 to 10 sec ADEV noise of a good
oscillator because of the TICs high noise floor due to it's limited
A 1 second noise floor of 1e-11, requires a time interval resolution of
The good news is that many time nuts have a great TIC counter with that
capability and do not even know it.
A stand alone Tbolt, IN THE MANUAL DISABLED MODE, WITH A GOOD ANTENNA SETUP,
makes a respectable TIC counter with resolution near 10 ps on it's PPT Freq
data output and near 100 ps using it's Phase data.
This gives a noise floor near e-11 at 1 sec and e-12 at 100 seconds, which
is low enough to test many of the good 10 MHz oscillators.
I find the Tbolt is the Only thing needed to do high precision mid and long
term performance testing of 10811s and LPRO Rbs
A Tbolt can give very useful data for making ADEV plots past 10 to 100
seconds for either an externally connected Osc (or for it's own internal
osc) in both the disciplined and disabled modes.
Attached are some 'TimeLab' ADEV plots comparing a stand alone TBolt-Tic
tester to a TPLL2.0
The data shows that a Tbolt can make accurate ADEV measurements on it's
own, down to 2e-12 past 100 sec when using the logged FREQ data.
The TBolt_Tic can also give very accurate long term data to 1e-13 in one day
by using it's phase output data when the Tbolt is in the DISABLE mode.
This allows the Freq nut an alternative to needing a special TIC counter (by
using an external osc Tbolt) or needing a separate reference Osc (by using
the GPS signal), when doing high performance testing.
The Tbolt plotted has it's internal Osc removed and uses an external 10 MHz
I made test plots with the TBolt driven from both a 10811 and a LPRO using
the GPS as the reference signal.
Like all testers, the noise measurement is limited by the reference used,
so it is very Important to get the Best GPS signal possible to the TBolt,
which includes but is not limited to,
Having a good sky view, getting the fixed location accurate and taking the
short term data when the satellites are not switching.
Very Important note, The above is NOT available directly from LadyHeather's
ADEV plots (at least not yet - Mark is a revision coming?),
What one needs to do is to log the Tbolt's Freq and Phase data at the 1 sec
rate and then use that data with an external ADEV program such as Ulrich's
Plotter or John's TimeLab.
Note for TimeLab users. LH adds some extra comment data lines in it's log
file that need to be manually removed before using the data file with some
versions of TimeLab.
Another very useful thing that can be done with LadyHeather and a Tbolt that
has been set up to use an external osc (and has a good antenna system),
is to measuring or set the frequency of any external 10 MHz Osc.
Short summery of how;
Put the TBolt in the Manual disable mode, (D D)
The Oscillator's EFC input and the Tbolt's Dac output are NOT connected or
Use the (J J) command to rezero the Phase plot (plus the cable delay if
and then read or adjust the Osc freq on the ppt plot.
With LadyHeather's filter off (F D 0) useful resolution is about 1e-10 in
With the filter set to 10 sec (F D 10) useful resolution is near 1e-11 in
well under one minute
With the filter set to 100 sec, resolution is around 1e-11 in a few minutes.
adding a trend line helps (G O L)
For higher accuracy and resolution, watch the Phase change trend over a
couple hours using (G P L),
This can provide useful resolution as low as 1e-12. (delta 3.6 ns per hr = a
1e-12 freq offset)
If you want even more accuracy, watch the PHASE change over a few days. This
can check your best Primary Cs standard's frequency.
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