Meinberg GPS170PCI, Руководство пользователя

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Page 10 7 Installing the radio clock
slot cover. After the computer has been restarted, the monitor software can be run in order to check the clock's
conguration.The computers case should be closed again and the antenna must be connected to the appropriate
connector.
7.3 Powering up the system
After the board has been mounted and the antenna has been connected, the system is ready to operate. About
10 seconds after power-up the receivers TCXO operates with the required accuracy. If the receiver nds valid
almanac and ephemeris data in its battery buered memory and the receivers position has not changed signif-
icantly since its last operation the receiver can nd 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 at least one
minute after power-up. After 20 minutes of operation the TCXO has achieved its nal accuracy and the generated
frequencies are within the specied tolerances.
If the receiver position has changed by some hundred kilometers since last operation, the satellites real ele-
vation 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. In the default mode of operation, neither pulse outputs nor the serial ports will be enabled after
power-up until synchronization has been achieved.
However, it is possible to congure some or all of those outputs to be enabled immediately after power-up.
If the system starts up in a new environment (e. g. receiver position has changed or new power supply) it can
take some minutes until the TCXOs output frequency has been adjusted. Up to that time accuracy of frequency
drops to 10-8 reducing the accuracy of pulses to +-2
µ
s.
7.3.1 Mounting the GPS Antenna
The GPS satellites are not stationary, but circle round the globe with a period of about 12 hours. They can only
be received if no building is in the line-of-sight from the antenna to the satellite, so the antenna/downconverter
unit must be installed in a location that has as clear a view of the sky as possible. The best reception is achieved
when the antenna has a free view of 8
◦
angular elevation above the horizon. If this is not possible, the antenna
should be installed with the clearest free view to the equator, because the satellite orbits are located between
latitudes 55 ◦ North and 55 ◦ South. If this is not possible, you may experience diculty receiving the four satellites
necessary to complete the receiver's position solution.
The unit can be mounted using a pole with a diameter up to 60 mm. A standard coaxial cable with 50
Ω
impedance (e.g. RG58C) should be used to connect the antenna/converter unit to the receiver. Cable thinner
than RG58 should be avoided due to its higher DC resistance and RF attenuation. When using the optional
antenna diplexer the total length of one antenna line between antenna, diplexer and receiver must not be longer
than 300 m. If a cable with less attenuation is used its length may be increased accordingly (e.g. 700 m with
RG213).
Up to four GPS170 receivers can be run with one antenna/downconverter unit by using an optional antenna
splitter. The total length of one antenna line between antenna, splitter and receiver must not be longer than the
max. length shown in the table above. The position of the splitter in the antenna line does not matter.
High voltage protectors must be installed directly after reaching the indoors. The optional delivered protec-
tion kit is not for outdoor usage.
10 Date: 12th July 2012 GPS170PCI