Impairments To Line-of-sight Propagation
Low-powered microwave transmitters can be foiled by tree branches, or even heavy rain or snow.
If a direct visual fix cannot be taken, it is important to take into account the curvature of the Earth when calculating line-of-sight from maps.
The presence of objects not in the direct visual line of sight can interfere with radio transmission. This is caused by diffraction effects: for the best propagation, a volume known as the first Fresnel zone should be kept free of obstructions.
Reflected radiation from the ground plane also acts to cancel out the direct signal. This effect, combined with the free-space r−2 propagation loss to a r−4 propagation loss. This effect can be reduced by raising either or both antennas further from the ground: the reduction in loss achieved is known as height gain.
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