Westermo RM-505U-2-E - Manual (Page 21)

User Manual
MAN_505_1.7.DOC Page 21
not possible to achieve reliable communications, a 105U module may be used to receive the
message and re-transmit it. This module is referred to as a repeater. This module may also have
input/output (I/O) signals connected to it and form part of the I/O network.
An antenna must be connected to each 505U module using the BNC female connector that
protrudes though the top of the enclosure.
To achieve the maximum transmission distance, the antennas should be raised above intermediate
obstructions so the radio path is true “line of sight”. Because of the curvature of the earth, each
antenna will need to be elevated at least 5 metres above ground for paths greater than 5 km (3
miles). The modules will operate reliably with some obstruction of the radio path, however the
reliable radio range is decreased. Obstructions that are close to either antenna will have more of a
blocking effect than obstructions in the middle of the radio path.
Small whip antennas may be connected directly to the 505U module. Other antennas may be
connected to the module via 50 ohm coaxial cable (eg RG58 or RG213) terminated with a male
BNC connector. 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.
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. There are several types of antennas suitable for use on
unlicensed frequency channels. It is important that the antenna is chosen carefully to avoid
contravening the maximum power limit on the unlicensed channel - if in doubt refer to an authorised
service provider.
Connections between the antenna and coaxial cable should be carefully taped to prevent ingress of
moisture. Moisture 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 vulcanising
tape such as “3M 23 tape”, with a secondary layer of PVC insulating tape.
Where antennas are mounted on elevated masts, the masts should be effectively earthed to avoid
lightning surges. Surge suppression devices are recommended if lightning surge problems are likely in
the installation area. 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.
Whip antenna
A whip antenna is a small rubber coated antenna designed to connect directly to the 505U BNC
connector. It is suitable for applications up to 25% of the maximum distance for the power level.
Although the antenna has a negative gain (the power transmitted by the antenna is less than that
produced by the module), it is easy to use and low cost.