Time Correction with PPS Signal Disciplined by GPS Receiver

Paolo Zoccarato, Tommaso Occhipinti,

Ivan Capraro, Pietro Bolli, Filippo Messina, Massimiliano Belluso

PPS data analysisMini-T Trimplespecification:

About 600 counts, i.e. ~15 ns

About 2150 counts, i.e. ~ 54 ns

Counts of the pps signal

Counts differences of the pps signal

PPS acquired duringFeige observation

Estimation of the initial reference period

2t7242659940.00102416-t 29556890.87303907- 2.98174095974811)( ty

Fit curve equation:

Removing the linear andquadratic terms we obtain:

On average there is a 1 ppsevery 40959748112.9816 counts,

then the real length of theTDC initial reference period is:

[s] 012-372858e24.41421262.98164095974811

1rT

670 counts

PPS timeThe estimation error is about137 counts, i.e. ~3.4 ns

Determined the real initial reference period weconvert the counts in time:

Now we must remove the residual errorrespect to the ideal time due tothe oscillator drift and offset

Oscillator parameters estimation

2t011-967923e2.74415126-t009-040407e9.40448039006-5851426e-1.1652824)( ty

The fit curve equation is:

The fit error is about 360 ns:

Removing the oscillator offset and driftwe obtain the stochastic residual of theoscillator:

011-6967923e-2.7441512d

009-040407e9.40448039f

006-5851426e-1.1652824

0

0

0

e

2000 )(_)(_)(_)(_ itagtimeditagtimefeitagtimeitagtime

The estimated initial error phase,offset and drift coefficients

can be used to correct the time tags of Feige.

Oscillators stochastic noise

W = white, F = flicker, RW = random walk,FM = frequency modulation, PM = phase modulation

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.

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).

Rubidium Analysis in Cagliari