Chapter Two
Installation
Man_455U-D Rev 3.07
Page
23
antenna can radiate a large amount of RF energy. It is important to ensure that a person cannot
approach the antennas within the recommended minimum safe distances in the table below.
Antenna Type
Minimum safe distance
(450MHz)
Minimum safe distance
(60/150/220MHz)
Dipole
0.4 metres
0.2 metres
3dBd Collinear
0.7 metres
0.4 metres
6dBd Collinear
0.9 metres
N/A
6 element Yagi
1.2 metres
N/A
9 element Yagi
1.5 metres
N/A
16 element Yagi
2.3 metres
N/A
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.
Wavelengths
450 MHz 66 cm
COLINEAR
ANTENNA
MAST
MODEM
SURGE ARRESTOR
(OPTIONAL)
COAXIAL CABLE
WEATHERPROOF
CONNECTORS WITH “3M
23
” TAPE
PROVIDE GOOD GROUND
CONNECTION TO MAST, MODULE AND
SURGE ARRESTOR
GND
1 Wavelength minimum
IF GROUND CONDITIONS ARE POOR,
INSTALL MORE THAN ONE STAKE
STRESS RELIEF LOOP
220 MHz 163 cm
150 MHz 200 cm
