User's Manual

455U-D Radio Modem Module User Manual
Page 22 © Jan 2008
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 metres RG213 - 20 metres. Note
that this applies to marginal paths only - if the radio path has a strong radio signal, then longer
1m minimum
COLINEAR
ANTENNA
MAST
EARTH STAKE
IF GROUND CONDITIONS ARE
POOR, INSTALL MORE THAN
ONE STAKE
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
455U