Phoenix Contact FL WLAN 24 AP 802-11, User Manual, Page: 12 / 122

Factory Line - Wireless LAN
1-4
PHOENIX CONTACT 7190_en_02
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.
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.
Figure 1-3 Effects on radio signals
Table 1-1 Free space attenuation in the 2.4/5 GHz ISM band
Distance 5 m 10 m 25 m 50 m 100 m 500 m 1000 m
Attenuation 54 dB 60 dB 68 dB 75 dB 80 dB 94 dB 100 dB At 2.4 GHz
Attenuation 61 dB 67 dB 75 dB 82 dB 87 dB 100 dB 107 dB At 5 GHz
Dispe r sion
Re fl ection
Bendin g
Abso r ption
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