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When the unit is powered from a battery or a high current supply, connect a fast 1.25A fuse in line with the
positive supply. This protects the power cabling and modem.
6.2.2
Securing the modem
Before securing the modem take into account the amount of additional space required for the mating
connectors and cables that will be used in the application.
Where access is restricted, it may be easier to connect all the cables to the modem prior to securing it in
the application.
Securely attach the GT910 G terminal modem to the host application using two 3mm diameter pan-head
screws.
6.3
Antenna
6.3.1
General
The antenna is the component in your system that maintains the radio link between the network and the
modem. Since the antenna transmits and receives electromagnetic energy, its efficient function will
depend on:
the type of antenna (for example, circular or directional);
the placement of the antenna;
Communication disturbances in the vicinity of the antenna.
The following sections address issues concerning antenna type, antenna placement, antenna cable, and
possible communication disturbances. In any event, you should contact your antenna manufacturer for
additional information concerning antenna type, cables, connectors, antenna placement, and the
surrounding area. You should also determine whether the antenna needs to be grounded or not. Your
antenna manufacturer might be able to design a special antenna suitable for the application.
6.3.2
Antenna type
Make sure that the selected antenna meets the requirements specified in Section 4.2 (“Antenna
Connector”).
6.3.3
Antenna placement
The antenna should be placed away from electronic devices or other antennas. The recommended
minimum distance between adjacent antennas, operating in a similar radio frequency band, is at least
50cm. If signal strength is weak, it is useful to face a directional antenna at the closest radio base station.
This can increase the strength of the signal received by the modem. The modem’s peak output power
can reach 2W. RF field strength varies with antenna type and distance. At 10cm from the antenna the
field strength may be up to 70V/m and at 1m it will have reduced to 7V/m. In general, CE-marked
products for residential and commercial areas, and light industry can withstand a minimum of 3V/m.
6.3.4
The antenna cable
Use 50Ω impedance low-loss cable and high-quality 50Ω impedance connectors (frequency range up to
2GHz) to avoid RF losses. Ensure that the antenna cable is as short as possible. The Voltage Standing-
Wave Ratio (VSWR) may depend on the effectiveness of the antenna, cable and connectors. In addition,
if you use an adapter between the antenna cable and the antenna connector, it is crucial that the antenna
cable is a high-quality, low-loss cable. Minimize the use of extension cables, connectors and adapters.
Each additional cable, connector or adapter causes a loss of signal power.
