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Network planning
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Both vegetation and construction can grow. Especially when planning a high data rate hop which
requires a near-LOS terrain profile, take into consideration the possible future growth of obstacles.
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When the signal passes a considerable amount of vegetation (e.g. a 100m strip of forest), think of
the season. Typically the path loss imposed by vegetation increases when the foliage gets dense
or wet (late spring, rainy season). Hence the fade margin should be increased if your field measure-
ments are done in a dry autumn month. The attenuation depends on the distance the signal must
penetrate through the forest, and it increases with frequency. According to a CCIR, the attenuation
is of the order of 0.05 dB/m at 200 MHz, 0.1 dB/m at 500 MHz, 0.2 dB/m at 1 GHz. At lower frequen-
cies, the attenuation is somewhat lower for horizontal polarization than for vertical, but the difference
disappears above about 1 GHz.
•
Though being a rare problem, moving metallic objects may cause serious disruptions, especially
when they are close to one end of the radio hop. They may be cars on a highway, blades of a wind
turbine, planes taking off from a nearby airport runway etc.
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Even when the signal is very strong, be careful when considering various cheap whips or more
generally any antennas requiring a ground plane to function properly. A tempting scenario is to use
the body of the metallic box, where the radio modem and connected application equipment (often
a computer) is installed, as the ground plane, which leads to never-ending problems with locally
generated noise. The ground plane forms an integral part of such an antenna, hence it has to be
in a safe distance (several metres) from any electronic equipment as well as the antenna itself. A
metallic plate used as shielding against interference must not form a part of the antenna.
Fig. 3.8: Antenna mounting
38
incorectly
Power supply
RTU
correctly
RipEX Radio modem & Router – © RACOM s.r.o.
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