User manual

Chapter Two Installation
man_905-105_2.9 Page 13
loss. For example, a 6 element Yagi with 70 feet (20 metres) of Cellfoil has a net gain of 4dB
(10dB – 6dB).
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 vulcanising tape such as “3M 23 tape”, and finally with another layer of PVC
UV Stabilised insulating tape. The first layer of tape allows the joint to be easily inspected when trouble
shooting as the vulcanising 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 15 ‘ cable does not require any additional coaxial
cable, however a cable must be used with the collinear antennas.
Collinear and dipole antennas should be mounted vertically, preferably 1 metre away from a wall or
mast to obtain maximum range.
1m minimum
COLINEAR
ANTENNA
MAST
EARTH STAKE
IF GROUND CONDITIONS ARE
POOR, INSTALL MORE THAN
INSTALL AERIAL ABOVE
LOCAL OBSTRUCTIONS
ANT
905U
SURGE
ARRESTOR
(OPTIONAL)
COAXIAL CABLE
WEATHERPROOF
CONNECTORS WITH
“3M 23” TAPE
STRESS RELIEF LOOP
PROVIDE GOOD
GROUND
CONNECTION TO
MAST, MODULE
AND SURGE
ARRESTOR
GND