Transcript Time Correction with PPS Signal Disciplined by GPS Receiver

Time Correction with PPS Signal
Disciplined by GPS Receiver
Paolo Zoccarato, Tommaso Occhipinti,
Ivan Capraro, Pietro Bolli, Filippo Messina,
Massimiliano Belluso
Counts of the pps signal
PPS data analysis
Mini-T Trimple
specification:
PPS acquired during
Feige observation
Counts differences of the pps signal
About 600 counts, i.e. ~15 ns
About 2150 counts, i.e. ~ 54 ns
Estimation of the initial reference period
Fit curve equation:
y(t )  4095974811
2.9817- 0.87303907
2955689 t - 0.00102416
724265994 t 2
Removing the linear and
quadratic terms we obtain:
670 counts
On average there is a 1 pps
every 40959748112.9816 counts,
then the real length of the
TDC initial reference period is:
Tr 
1
 24.4142126 372858e - 012 [s]
4095974811 2.9816
PPS time
The estimation error is about
137 counts, i.e. ~3.4 ns
Determined the real initial reference period we
convert the counts in time:
Now we must remove the residual error
respect to the ideal time due to
the oscillator drift and offset
Oscillator parameters estimation
The fit curve equation is:
y(t )  -1.1652824
5851426e- 006 9.40448039
040407e- 009 t - 2.74415126
967923e- 011 t 2
The fit error is about 360 ns:
Removing the oscillator offset and drift
we obtain the stochastic residual of the
oscillator:
e0  -1.1652824
5851426e- 006
f 0  9.40448039
040407e- 009
d 0  -2.7441512
6967923e- 011
The estimated initial error phase,
offset and drift coefficients
can be used to correct the time tags of Feige.
time_ tag(i)  time_ tag(i)  e0  f0  time_ tag(i)  d0  time_ tag(i)2
Oscillators stochastic noise
The stochastic residuals are on the
order of 10-6 [sec], according with the
values of a quartz oscillator.
The residual noise is a flicker phase
noise (see figure above), the
predominant noise on the Quartz
oscillators in the short period, as it is
possible to see in the table at the right.
W = white, F = flicker, RW = random walk,
FM = frequency modulation, PM = phase modulation
Crab analysis
• We have realized two Matlab functions to
correct the time tags.
• To correct the Crab data we don’t have the
pps data, so we used pps data acquired
during Feige Observation
• The period of the Crab without this
correction is 30.61 ms, while with the
correction is 33.61 ms.
• Crab period became very close to its real
period (33.71 ms).
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