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5. INSTALLATION OF THE MODEM
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LZT 123 7361 R1B
• the VSWR value should be less than 3:1 to avoid damage to the
modem.
5.3.3 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.
5.3.4 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.
5.3.5 Possible Communication Disturbances
Possible communication disturbances include the following:
• Noise can be caused by electronic devices and radio transmitters.
• Path-loss occurs as the strength of the received signal steadily
decreases in proportion to the distance from the transmitter.
• Shadowing is a form of environmental attenuation of radio signals
caused by hills, buildings, trees or even vehicles. This can be a
particular problem inside buildings, especially if the walls are thick
and reinforced.
• Multi-path fading is a sudden decrease or increase in the signal
strength. This is the result of interference caused when direct and
reflected signals reach the antenna simultaneously. Surfaces such as
buildings, streets, vehicles, etc., can reflect signals.