Wireless LAN – WLAN
BAT54-Rail/F..
Release
7.54
06/08
3.8
Establishing outdoor wireless networks
113
To ensure an optimal signal reception between transmitter and receiver, the
Fresnel zone 1 should remain free from any obstruction. Any disturbances
from elements protruding into this zone will significantly reduce the effective
signal power. The object not only screens off a portion of the Fresnel zone,
but the resulting reflections also lead to a significant reduction in the signal
reception.
The radius (R) of Fresnel zone 1 is calculated with the following formula as-
suming that the signal wavelength (
λ) and the distance between transmitter
and receiver (d) are known.
R = 0.5 *
√ (λ * d)
The wavelength in the 2.4-GHz band is approx. 0.125m, in the 5-GHz band
approx. 0.05 m.
Example: With a separating distance of 4 km between the two antennae, the
radius of Fresnel zone 1 in the 2.4-GHz band is 11 m, in the 5-GHz band 7 m.
To ensure that the Fresnel zone 1 remains unobstructed, the height of the an-
tennae must exceed that of the highest obstruction by this radius. The full
height of the antenna mast (M) should be as depicted:
Fresnel zone 1
Fresnel zone 2
Fresnel zone 3
D
i
s
t
a
n
c
e
d
Radius R
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