Specifications

Appendix C
Results obtained during
development
A lot of testing was performed to verify the method (see [4]). The first tests were intended to
check the GPS cards and to see how well they behave. Then some tests and measurements
were done to see if the synchronization method is working.
C.1 Testing the GPS card
The GPS card can provide position and timing information to the host computer. Using
a small utility program ( mbgstatus ) that comes from the manufacturer (Meinberg) we
gathered all positional parameters delivered by the GPS. The test was done using a GPS
card that had the antenna on the roof of a building and the card rep orted full strength
satellite signal and 9 satellites in view.
The values were written to some files and analyzed and plotted using Matlab. We recorded
the altitude, latitude, longitude and x, y, z coordinates. A full set was parameters was read
from the GPS every 5 seconds for several days. The Figure C.1 shows the graphs of these
parameters as they vary in time. There are large variations (especially for the altitude
which varies with 100 meters) but the manufacturer says that this is normal and it does
not affect the timing accuracy.
C.2 Local synchronization test
This test was done on a computer with 2 clock cards (master and slave) that were driven
by the same GPS card (hosted by the same computer). We synchronized the clocks and
then we took s ample values of the clock counter at each pulse on the 1Hz PPS wire from
the GPS. The samples did not differ by more than one clock tick (because of the phase shift
between the 10MHz and the 1Hz signals) so the results were satisfactory.
Another measurement was done to see the duration of one second in clock ticks. As we
said before, the GPS provides a 10MHz signal and the clock boards derive from it a 40MHz
signal, so the duration of one second should by always 40000000 clock ticks. We measured
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