Fading Effect - Aastra Messkoffer Bedienungsanleitung

Basics
The same principle applies to all antenna types: The narrower the horizontal and vertical radiation
range, the greater the distances that can be covered. In this connection we talk of antenna gain,
which indicates the ratio of the energy radiated in a particular angle to the radiated energy of a
standard antenna (usually a l/2 dipole antenna). An extreme example of this is the radio relay
antenna, which is used for transmitting radio signals in a targeted direction from one point to the
next.
Note
When using external antennas, the cable length between base station and antenna should be as
short as possible because the attenuation of the radio signals in send and receive direction is not to
be neglected in this frequency range (approx. 1.5dB per meter for a normal cable). A 4-meter long
cable thus compensates for an antenna gain of 6dB. In any case it may be useful to consider using a
special low-attenuation cable.

Fading Effect

If an base station is operated with external antennas, an antenna must always be connected to each
of the two antenna connections.
The antennas should have the same radio characteristic and also cover the same range. This reduces
the occurrence of fading effects (caused by radio signals cancelling one another out through reflec-
tions), and considerably improves the connection quality.
If such an effect occurs on one of the antennas, the base station automatically switches over to the
second antenna, thereby preventing minor drop-outs. This is referred to as antenna diversity. Fading
effects occur mainly inside and between buildings, which provide a great deal of reflection surface.
Dual antennas inside a single housing, designed specifically with this effect in mind, are widely
available in the market. That is why the base stations themselves are always equipped with two
internal antennas.
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