Fading Effect - Mitel SIP-DECT Site Survey Kit User Manual

SIP-DECT Site Survey Kit User Guide
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 the 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 a 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 reflections), 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.
24