Chapter Two
Installation
Page 11
© April 2007
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 gains and losses of typical antennas are
Antenna
Gain (dB)
3dB Collinear
3
6dB Collinear
6
6 element Yagi
10
Cable type
Loss (dB per 10 m)
RG58
-5
RG213
-2.5
Cellfoil
-3
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 20 metres of RG58 has a net gain of 0 dB
(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 problems
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 vulcanizing
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.
2.2.1 Dipole and Collinear antennas.
A collinear antenna transmits the same amount of radio power in all directions - as such that
are easy to install and use. The dipole antenna with integral 5m cable does not require any
additional coaxial cable, however a cable must be used with the collinear antennas.
