Meinberg GPS169PCI - Manual (Page 8)

8
GPS169PCI features
The satellite controlled clock GPS169PCI is a plug-in board designed for computers
with 3.3V or 5V PCI bus running with clock frequencies of 33MHz or 66 MHz. The
rear slot cover integrates the antenna connector, the modulated timecode, two status
LEDs, and a 9 pin sub-D male connector.
The antenna/converter unit is connected to the receiver by a 50
Ω coaxial cable with
length up to 250m. Power is supplied to the unit DC insulated across the antenna cable.
Optionally, an overvoltage protection and an antenna distributor are available. The
antenna distributor can be used to operate up to 4 Meinberg GPS receivers using a
single antenna/converter unit.
The navigation message coming in from the satellites is decoded by satellite clock's
microprocessor in order to track the GPS system time with an accuracy of better than
250nsec. Compensation of the RF signal´s propagation delay is done by automatical
determination of the receiver´s position on the globe. A correction value computed
from the satellites´ navigation messages increases the accuracy of the board´s tempera-
ture compensated master oscillator (TCXO) to ±5•10
-9 and automatically compensates
the TCXO´s aging. The last recent value is restored from the non-volatile memory at
power-up. Optionally, the clock is also available with a higher precision time base.
A monitoring software shipped with the board can be used to check the clock's status
and configure some operational parameters.
Time zone and daylight saving
GPS system time differs from the universal time scale (UTC) by the number of leap
seconds which have been inserted into the UTC time scale after GPS has been initiated
in 1980. The current number of leap seconds is part of the navigation message supplied
by the satellites, so the satellite clock´s internal real time is based on UTC. Conversion
to local time including handling of daylight saving year by year can be done by the
receiver´s microprocessor. For Germany, the local time zone is UTC + 3600 sec for
standard time and UTC + 7200 sec if daylight saving is in effect.
The clock's microprocessor determines the times for start and end of daylight saving
time by a simple algorithm e. g. for Germany:
Start of DST is on the first Sunday after March, 25th, at 2 o'clock standard time.
End of DST is on the first Sunday after October, 25th, at 3 o'clock daylight time.
The monitoring software shipped with the board can be used to configure the time zone
and daylight savings parameters easily. Switching to daylight saving time is inhibited
if for both start and end of daylight saving the parameters are exactly the same.
The timecode (IRIG, AFNOR, IEEE) generated by GPS169PCI is available with
these settings or with UTC as reference. This can be set by the monitor program.