Meinberg SHSPZF LANTIME - Manual (Page 25)

Powering Up the System
When the LANTIME/SHS is switched on the SHS STATE menu is displayed
because the two receivers (GPS and PZF) are usually not synchronized yet. After the
configured time limit is reached the LANTIME/SHS goes to normal operation. The
following notes should be taken into consideration:
- the GPS antenna/converter unit must be installed in a location from which as
much of the sky as possible can be seen (see "Mounting the GPS antenna")
- the PZF antenna must be positioned to optimise the correlation better than 60 %
- the distance to the German long wave transmitter have to be configured
- the time limit (the max. accepted time difference between GPS and PZF) has to
be set to the needed accuracy (default 10 ms)
Some menues can be called not before the single board computer has booted. Because
of this the state menues for the PZF and the setup for the LAN parameters can not be
edited until the bootphase has finished (approx. 1 minute).
Booting the GPS receiver
If both the antenna and the power supply have been connected the system is ready
to operate. About 10 seconds after power-up the receiver’s oscillator has warmed up
and operates with the required accuracy. If the receiver finds valid almanac and
ephemeris data in its battery buffered memory and the receiver’s position has not
changed significantly since its last operation the receiver can find out which satellites
are in view now. Only a single satellite needs to be received to synchronize and
generate output pulses, so synchronization can be achieved maximally one minute
after power-up.
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If the receiver position has changed by some hundred kilometres since last operation,
the satellites´ real elevation and Doppler might not match those values expected by
the receiver thus forcing the receiver to start scanning for satellites. This mode is
called Warm Boot because the receiver can obtain ID numbers of existing satellites
from the valid almanac. When the receiver has found four satellites in view it can
update its new position and switch to Normal Operation. If the almanac has been
lost because the battery had been disconnected the receiver has to scan for a satellite
and read in the current almanacs. This mode is called Cold Boot. It takes 12 minutes
until the new almanac is complete and the system switches to Warm Boot mode
scanning for other satellites.
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