Westermo RM-80 - Manual (Page 9)

9 6193-4201
An antenna should be connected to the module via 50 ohm coaxial cable (eg RG58,
RG213 or Cellfoil) terminated with a male SMA coaxial connector. The higher the
antenna is mounted, the greater the transmission range will be, however as the length
of coaxial cable increases so do cable losses. For use on unlicensed frequency channels,
there are several types of antennas suitable for use. It is important antenna are chosen
carefully to avoid contravening the maximum power limit on the unlicensed channel – if
in doubt refer to an authorized service provider.
The net gain of an antenna/cable configuration is the gain of the antenna (in dBi) less the
loss in the coaxial cable (in dB).
The maximum net gain of the antenna/cable configuration permitted is 0dB.
The net gain of the antenna/cable configuration is determined by adding the antenna gain
and the cable loss. For example, a 6 element Yagi with 20metres of RG58 has a net gain
of 0dB (10dB – 10dB).
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 prob-
lems with radio systems, as it greatly increases the radio losses. We recommend that the
connection be taped, firstly with a layer of PVC Tape, then with a vulcanizing tape such as
“3M 23 tape”, and finally with another layer of PVC UV Stabilized insulating tape. The first
layer of tape allows the joint to be easily inspected when trouble shooting as the vulcan-
izing seal can be easily removed.
Where antennas are mounted on elevated masts, the masts should be effectively earthed
to avoid lightning surges. For high lightning risk areas, surge suppression devices between
the module and the antenna are recommended. 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.