Lancom 1723 VOIP User Manual page 88

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Chapter 8: Advanced wireless LAN configuration
To ensure that the Fresnel zone 1 remains unobstructed, the height of the
antennas 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
Radius R
ANTENNA ANTENNA
Security: 1m
Obstruction height H
OBSTRUCTION
PRODUCTION
ADMINISTRATION WLAN Router WLAN Router
Earth's curvature E
M = R + 1m + H + E (earth's curvature)
The allowance for the curvature of the earth (E) can be calculated at a distance
(d) as E = d² * 0.0147 – i.e. at a distance of 8 km this is almost 1m
Example: With a distance of 8 km between the antennae, the result in the
2.4-GHz band is a mast height above the level of the highest obstruction of
approx. 13 m, in the 5-GHz band 9 m.
Antenna power
The power of the antennas must be high enough to ensure acceptable data
transfer rates. On the other hand, the country-specific legal regulations
regarding maximum transmission power should not be exceeded.
The calculation of effective power considers everything from the radio module
in the transmitting access point to the radio module in the receiving access
point. In between there are attenuating elements such as the cable, plug con-
nections or simply the air transmitting the signals and amplifying elements
such as the external antennas.
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