Westermo RM-505U-2-E - Manual (Page 22)

505U Radio Telemetry Module
Page 22 © September 2002
Dipole antenna.
A unity gain dipole is the normal antenna for use on unlicensed channels. As it does not provide any
gain, then the power transmitted from the antenna will be the same as the power out of the module.
Dipole antennas are available with a BNC connector for direct mounting on the 505U module, or
with coaxial cable for mounting away from the module. Dipole antennas should be mounted
vertically, at least 1 metre away from a wall or mast.
For marginal radio paths, the following lengths are the recommended maximum for the coaxial
cable to the dipole antenna: RG58 -10 metres RG213 - 25 metres. 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 25 metres of cable is required for a marginal
path installation, then a low loss cable such as RG9913, or a higher gain antenna should be used.
4mm 2
1m
DIPOLE AERIAL
MAST
EARTH CONDUCTOR
SHOULD BE 16mm
2
EARTH STAKE
IF GROUND CONDITIONS ARE POOR,
INSTALL MORE THAN ON STAKE
MAX. COAXIAL CABLE LENGTHS
RG58 – 10m
RG213 – 20m
INSTALL AERIAL ABOVE LOCAL
OBSTRUCTIONS
GND
ANT
505U
SURGE DIVERTER
COAXIAL CABLE SEAL CONNECTORS
WITH “3M 23” TAPE
STRESS REDUCTION LOOP
The 505U can produce 500mW of radio power when an external 12VDC supply is used, but only
250mW of power with internal batteries. This power may be boosted to 500mW by using a higher
gain antenna (3dB) such as a 3 element Yagi or a 3dB collinear antenna. These higher gain antennas
may also be used to compensate for coaxial cable loss. The losses are 3dB for every 10m of
RG58 and 1.5dB for every 10m of RG213. If 10m of RG58 cable is used on a marginal radio path,
then a higher gain antenna may be used to cancel the losses in the cable and boost the transmitted
power back to the maximum level. Note that you can accumulate gains - if you need 3dB to boost
250mW to 500mW and another 3dB to compensate for coaxial cable, then you can install a 6dB
gain antenna and be sure of transmitting the maximum power allowed.