Antenna Diversity; Polarization Diversity; Installing The Airlancer Extender Antennas - Lancom 1723 VOIP User Manual

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10.1.1

Antenna diversity

The transmission of radio signals can suffer from significant signal losses
because of reflection and scatter, among other reasons. In some areas, the
interaction with the reflected radio waves can cause a drop in signal strength,
or even cause it to be cancelled out completely. Transmission quality can be
improved with so-called "diversity" methods. The principle of "diversity"
methods relies on the fact that a transmitted signal is often received multiple
times (generally twice).
Each wireless LAN module is equipped with two send/receive units, each of
which can be connected to an antenna. In the case of antenna diversity, the
WLAN module checks which send/receive unit (antenna) is receiving the
strongest signal from a client. Only the stonger signal is used. The Access
Point stores the information on which send/receive unit was used to receive
data and proceeds to use the same unit for the transmission to the client.
Antenna diversity ensures that the various clients associated with the Access
Point always use the send/receive unit with the best signal.
10.1.2

Polarization diversity

Other diversity techniques process the two signals and combine them into a
single signal. The most common methods are space diversity and polarization
diversity. LANCOM Systems supplies various polarization diversity antennas
for connection to LANCOM devices. With these models, two orthogonally
polarized signals are received at a transmitter/receiver unit and combined to
form a single signal which is stronger than the two individual signals. This
improvement is the polarization gain.
10.1.3

Installing the AirLancer Extender antennas

The following diversity antennas are available as accessories for the LANCOM
VoIP Routers:
AirLancer Extender O-D80g (2.4 GHz band ), item no. 61221
AirLancer Extender O-D60a (5 GHz), item no. 61222
AirLancer Extender O-D9a (5 GHz), item no. 61224
Before mounting external antennas, please observe the information

on lightning protection in the LANCOM Outdoor Wireless Guide (sup-
plied or available as a download from www.lancom.eu). Mounting
antennas without adequate lightning protection could lead to serious
Chapter 10: Options and accessories
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