GPS7 GPS Synchronization and Timecode module
GPS/GLONASS antenna
requirements
The GPS7 module
requires an external antenna to receive GPS and/or GLONASS
signals from satellites. (See page 3-102, GPS receiver types.) You must set up an
antenna system to provide the GPS and/or GLONASS signal as an input to the
module. You can configure the instrument to provide 3.3 V or 5 V DC power for
the antenna.
WARNING. Prevent risk of shock or fire by ensuring that the GPS/GLONASS
antenna is p
rotected from lightning strikes when it is mounted outside a building
or facility. The GPS7 module and TG8000 mainframe do not have isolation
protection from lightning, so the facility installation must provide suitable
protection for the GPS/GLONASS antenna external to the TG8000 mainframe.
Failure to use appropriate precautions can result in injury or death.
CAUTION. To avoid antenna damage, do not turn on the DC antenna power until
you know that the antenna is designed to handle the selected voltage. Antenna
damage can occur if the antenna is not designed to handle the voltage you select.
The frequencies for GPS and GLONASS signals are slightly different. Be sure to
choose an antenna that supports all of the satellite constellations you intend to use.
When a GPS/GLONASS feed is first connected to the a ntenna input on the
module, it can take several minutes for the signal quality to reach its nominal
potential. How long that takes depends on such things as antenna site, cable
plant design, and available satellites. Excluding those variables, the typical time
to acquire satellites and achieve specified stability with a good satellite signal,
known position, and a warmed up instrument, is two minutes.
GPS/GLONASS antenna
system
Antenna systems vary depending on the operating environment and on safety and
regulatory requirements. A simplified typical system is shown in the following
figure to help you with planning and understanding the trade-offs of one set up
versus another. (See Figure 3-53.)
Figure 3-53: Simplified GPS/GLONASS antenna system
A GPS/GLONASS spe cific antenna with amplifier provides sufficient gain to
drive a reasonable length of cable, and provides filtering to reject signals at other
frequencies. A typical example of a GPS antenna is the Trimble Bullet III, 35 dB,
5V,antenna.
TG8000 Multiformat Test Signal Generator User Manual 3–103
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