Handbook

Axell Wireless Limited
Technical Literature
MWAA Primary F/O Head End Documentation
Primary Head End BDA 60-174303
Document Number 60-214802HBK Issue No. 1 Date 23/07/2009 Page 14 of 24
5. Maintenance
5.1. Fault Finding
5.1.1. Quick Fault Checklist
All Axell equipment is individually tested to specification prior to despatch. Failure of this type of
equipment is not common. Experience has shown that a large number of fault conditions relating to
tunnel installations result from simple causes often occurring as result of transportation, unpacking
and installation. Below are listed some common problems which have resulted in poor performance or
an indicated non-functioning of the equipment.
• Mains power not connected or not switched on.
• External connectors not fitted or incorrectly fitted.
• Internal connectors becoming loose due to transport vibration.
• Wiring becoming detached as a result of heavy handling.
• Input signals not present due to faults in the antenna and feeder system.
• Base transmissions not present due to fault at the base station.
• Modems fitted with incorrect software configuration.
• Changes to channel frequencies and inhibiting channels.
• Hand held radio equipment not set to repeater channels.
• Hand held radio equipment not set to correct base station.
5.1.2 Fault Isolation
In the event that the performance of the system is suspect, a methodical and logical approach to the
problem will reveal the cause of the difficulty.
Transmissions from the main base stations are passed though the system to the mobile radio
equipment; this could be a handheld radio or a transceiver in a vehicle. This path is referred to as the
downlink. The return signal path from the mobile radio equipment to the base station is referred to as
the uplink.
The first operation is to check the alarms of each of the active units and determine that the power
supplies to the equipment are connected and active.
This can be achieved remotely (via CEMS, the RS232 Coverage Enhancement Management System,
if fitted), or locally with the front door LEDs. The green LED on the front doors or front panels should
be illuminated, while the red alarm indicators should be off. If an Alarm is on, then that unit must be
tested against the original test specification.
If an amplifier is suspect, check the power supply to the unit. If no other fault is apparent use a
spectrum analyser to measure the incoming signal level at the input and then after reconnecting the
amplifier input, measure the output level. Consult with the system diagram to determine the expected
gain and compare result.
In the event that there are no alarms on and all units appear to be functioning it will be necessary to
test the system in a systematic manner to confirm correct operation.