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Factory Line - Wireless LAN
1-4
PHOENIX CONTACT
In the same way, each absolute value can be converted to a level. Example for 3 mW:
1.2.3
Free space attenuation
Electromagnetic waves are attenuated as they pass through media. Even air is a medium
that attenuates radio signals. The exponentially increasing attenuation through the medium
of air is known as free space attenuation. With a clear Fresnel zone (see "The Fresnel zone"
on page 1-7), free space attenuation can be calculated using the following formula:
For simple calculations in the 2.4 GHz ISM band, the expression
"32.4 + 20 x log 2400 MHz" can be replaced by the constant value 100.
Table 1-1
Free space attenuation in the 2.4/5 GHz ISM band
Distance
5 m
10 m
Attenuation
54 dB
60 dB
Attenuation
61 dB
1.2.3.1
Attenuation due to other effects
Radio signals are affected by obstacles and their surfaces, and in outdoor installations
variable factors such as rain, snow or humidity on surfaces also have an effect.
Dispersion
Bending
Figure 1-3
Effects on radio signals
25 m
50 m
68 dB
75 dB
67 dB
75 dB
82 dB
Absorption
100 m 500 m
1000 m
80 dB
94 dB
100 dB
87 dB 100 dB 107 dB
Reflection
719000009
At 2.4 GHz
At 5 GHz
7190_en_02
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