User's Manual

905U-D Radio Modem Module User Manual
Page 12 © May 2000
Chapter Two INSTALLATION
2.1 General
The 905U-D module is housed in an rugged aluminium case, suitable for DIN-rail mounting.
Terminals will accept wires up to 2.5 sqmm in size.
Normal 110-240V mains supply should not be connected to any terminal of the 905U-D
module. Refer to Section 2.3 Power Supply.
Before installing a new system, it is preferable to bench test the complete system.
Configuration problems are easier to recognise when the system units are adjacent.
Following installation, the most common problem is poor communications caused by
incorrectly installed aerials, or radio interference on the same channel, or the radio path being
inadequate. If the radio path is a problem (ie path too long, or obstructions in the way), then
higher performance aerials or a higher mounting point for the aerial may rectify the problem.
Alternately, use an intermediate 905U-D Module as a repeater.
The foldout sheet 905U-D Installation Guide provides an installation drawing appropriate to
most applications. Further information is detailed below.
Each 905U-D module should be effectively earthed via the "GND" terminal on the 905U-D
module - this is to ensure that the surge protection circuits inside the 905U-D module are
effective.
2.2 Aerial Installation
The 905U-D module will operate reliably over large distances. The distance which may be
reliably achieved will vary with each application - depending on the type and location of
aerials, the degree of radio interference, and obstructions (such as hills or trees) to the radio
path. See the 905U-D Installation Guide for expected ranges in your country. Note that the
expected range is for radio data rates of up to 4800 bits/sec. If 9600 bit/sec rate is
configured, the transmitted data will not have the same range. The radio range for 9600
bit/sec rate will be approx 70% of the range at lower data rates.
Where it is not possible to achieve reliable communications between two 905U-D modules,
then a third 905U-D module may be used to receive the message and re-transmit it. This
module is referred to as a repeater.
An aerial must be connected to each 905U-D module using the BNC female connector at the
top of the module.
To achieve the maximum transmission distance, the aerials should be raised above
intermediate obstructions such that the radio path is true “line of sight”. Because of the
curvature of the earth, the aerials will need to be elevated at least 5 metres above ground for
paths greater than 5 km (3 miles). For short distances, the modules will operate reliably with
some obstruction of the radio path. Obstructions which are close to either aerial will have
more of a blocking effect than obstructions in the middle of the radio path. For example, a
group of trees around the aerial is a large obstruction, and the aerial should be raised above
the trees. However if there is at least 100 metres of clear path before a group of trees, the
trees will have little affect on the radio path.