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9.3.3 Antenna placement
The antenna should be placed away from electronic devices and other antennas. The recommended
minimum distance between adjacent antennas, operating in a similar radio frequency band, is at least
50cm. If the signal strength is weak, it is useful to face a directional antenna towards 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 /commercial areas and the light industry can withstand a minimum of 3V/m.
9.3.4 The antenna cable
Use 50Ω impedance low-loss cable and high-quality 50Ω impedance connectors (frequency range up
to 3GHz) 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 adaptor 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.
9.3.5 Possible communications 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 which is caused when direct and reflected signals reach the antenna
simultaneously. Surfaces such as buildings, streets, vehicles, etc., can reflect signals.
•
Hand-over occurs as you move from one cell to another in the GSM network. Your mobile
application call is transferred from one cell to the next. Hand-over can briefly interfere with
communication and may cause a delay, or at worst, disruption.
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