Westermo RM-455U-D - Manual (Page 22)

Chapter Two Installation
Man_455U-D Rev 3.04 Page 23
Antenna Type Minimum safe distance
Dipole 0.4 metres
3dBd Collinear 0.7 metres
6dBd Collinear 0.9 metres
6 element Yagi 1.2 metres
9 element Yagi 1.5 metres
16 element Yagi 2.3 metres
Connections between the antenna and coaxial cable should be carefully taped to prevent
ingress of moisture. Moisture ingress in the coaxial cable is a common cause for problems
with radio systems, as it greatly increases the radio losses. We recommend that the
connection be taped with a layer of PVC insulating tape, then a layer of vulcanizing tape such
as “3M 23 tape”, with a final layer of PVC insulating tape.
Where antennas are mounted on elevated masts, the masts should be effectively earthed to
avoid lightning surges. Although the 455U-D module is fitted with surge protection,
additional surge suppression devices are recommended if lightning surge problems are
experienced. If the antenna is not already shielded from lightning strike by an adjacent earthed
structure, a lightning rod may be installed above the antenna to provide shielding.
2.2.1 3dB/6dB Collinear antenna.
A collinear antenna transmits the
same amount of radio power in all
directions - as such they are easy to
install and use. For marginal radio
paths, the following lengths are the
recommended maximum for the
coaxial cable to the antenna.
RG58 -10 meters, RG213 - 20
meters. Note that this applies to
marginal paths only - if the radio
path has a strong radio signal, then
longer lengths of cable (and hence
more cable loss) can be tolerated.
If more than 20 meters of cable is
required for a marginal path
installation, then a low loss cable
such as 10D-FB, or a higher gain
antenna should be used. Collinear
antennas should be mounted
vertically, at least 1 meter away
from a wall or mast.