Aastra 400 Series User Manual page 29

Fading Effect
If an SB-8ANT radio unit is operated with external antennas, an antenna must al-
ways 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 radio unit automatically switches over to
the second antenna, thereby preventing minor drop-outs. This is referred to as an-
tenna 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 radio units themselves are always equipped with two internal an-
tennas. For recommendations regarding manufacturers and antenna type please
contact Support.
Note:
If two individual antennas are used instead of a dual antenna, the installa-
tion clearance between the antennas must not be chosen at random but
adapted to the wavelength of the radio signals. If not, the antennas will
severely interfere with each other and mutually absorb a great deal of
energy. The recommended antenna clearance is twice the wavelength =
32 cm or a multiple of the wavelength = 48, 64, 80 or 96 cm. Clearances of
16 cm or in excess of 1 m are not recommended as this can cause other
types of interference.
Tip
A special completion test kit containing 4 antennas is available for meas-
uring with external antennas. It also contains a description (technical
information) with additional information about the antennas, tips on how
to use them and for other special situations. You can also find technical
information about the external antennas on the Aastra 400 Support
page.
Planning Aastra 400 DECT systems as of R1.0
syd-0457/1.0 – R1.0 – 10.2012
System characteristics
29