BECKHOFF CU8890-0000 - Manual (Page 19)

Operating Instructions
Attenuation and range
Fresnel Zone
Fresnel Zone In radio transmission, the space between the transmitting and receiving
antennas is known as the Fresnel zone. The Fresnel zone is a notional
spheroid between the antennas.
The main portion of the energy is transmitted in the area of the Fresnel
zone.
This zone should be free of obstructions (e.g. objects, houses, trees etc.).
Metal obstacles such as control cabinets, machine parts, pipelines, iron
beams etc. particularly hinder the development of the Fresnel zone!
Each hindrance of the Fresnel zone attenuates the transmission. If the
Fresnel zone is half obscured, for example, the additional attenuation is 6
dB, i.e. the field strength is reduced to half of the free field value. Reception
may then be disturbed or completely interrupted under certain
circumstances.
If the Fresnel zone is free from obstructions, the propagating wave is only
attenuated by the free field attenuation.
Radius r of the Fresnel zone in relationship to the distance s.
Attenuation in practice
Attenuation With an attenuation of 6 dB the range is shortened to half of the value for
an unobstructed connection, with 12 dB it is shortened to a quarter.
Material Attenuation Range approx. Example for an
unobstructed range
of 280 m
Thin wall 2-5 dB (free field range)/1.5 -
(free field range)/2 180 m - 140 m
Wooden wall 5 dB (free field range)/2 140 m
Masonry wall 6-12 dB (free field range)/2 -
(free field range)/4 140 m - 70 m
Concrete wall 10-20 dB (free field range)/4 -
(free field range)/8 70 m - 5 m
Concrete ceiling 20 dB (free field range)/8 < 35 m
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