Westermo RM-455U-D - Manual (Page 64)

Chapter Four Troubleshooting
Man_455U-D Rev 3.04 Page 65
4.5 Radio Path Testing
To carry out a radio path test, you will need two 455U modules. One module will be “fixed”
and the other “mobile”. Both units will need power supplies and antennas. The power supply
for the mobile unit is normally a 12V battery, but make sure that the battery is fully charged -
batteries with low voltage will lead to low radio power which will affect the test result.
The object of the test is to determine whether radio paths are reliable, marginal or unreliable.
A reliable path will have a margin of at least 10dB above the minimum required signal level
in good weather - this margin is enough to ensure that the radio path remains reliable in poor
conditions, and with changes in antennas and environment over time. A marginal path will
work reliably in good conditions, however may fail during poor conditions or if the landscape
changes over time. A margin of 10 dB is recommended as a safe minimum.
Set up as per section 4.4.1 to carry out a BER test.
Procedure:
 Configure the modules on the bench to communicate with each other in unacknowledged
mode.
 When the modules are close to each other, carry out a BER test without any antennas
connected, to make sure that the modules will communicate with each other.
 Set up the fixed module in one of the test positions - this is normally at a control centre or
repeater site. Fix the antenna in a temporary fashion. You will need to make an initial
assessment on how high the antenna should be mounted.
 Take the mobile module to the other end of the radio path. The antenna at this end can be
either held by the tester, or fixed in a temporary fashion. Note that a person’s body will
affect the radiation pattern of an antenna, so if the antenna is hand-held and the test is not
successful, try again with the antenna fixed to a 1 metre length of plastic pipe or timber.
The tester holds the length of pipe or timber with the antenna above head height.
 Test the radio path by AT#B command, or the communications test command in the
configuration software
 Record these measurements for comparison later during commissioning or if the system
has problems later.
If the radio path test is not successful:
1. Increasing the height of the antenna at either module, or at both modules can significantly
improve the result. Sometimes moving the antenna to the side helps, if there is an obvious
obstruction in the radio path.
2. Change one or both antennas to a higher gain if regulations allow.
3. Use a shorter coaxial cable between the antenna and the 455U.(this may involve moving
the 455U nearer to antenna mounting), or use a different coaxial cable with lower loss.
4. If a reliable radio path is not possible because of distance or path obstructions, you will
need to consider using a repeater module. The ideal repeater is another module in the