User Manual

Axell Wireless Limited
Technical Literature
L.A. M.T.A. Remote Sites
Document Number 80-301401HBKM Issue No. 1 Date 13/06/2008 Page 140 of 148
6. MAINTENANCE
6.1 Fault Finding
6.1.1 Quick Fault Checklist
All tunnel 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.
x Mains power not connected or not switched on.
x External connectors not fitted or incorrectly fitted.
x Internal connectors becoming loose due to transport vibration.
x Wiring becoming detached as a result of heavy handling.
x Input signals not present due to faults in the antenna and feeder system.
x Base transmissions not present due to fault at the base station.
x Modems fitted with incorrect software configuration.
x Changes to channel frequencies and inhibiting channels.
x Hand held radio equipment not set to repeater channels.
x Hand held radio equipment not set to correct base station.
6.1.2 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. The System consists of modules fitted in enclosed
shelves within a rack mounted, environmentally protected enclosure.
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 the volt free dry contact outputs to SCADA), or locally with the
front panel LEDs. The green LED on the front panel should be illuminated, while any red alarm
indicators should be off. If an Alarm is on, then that individual shelf must be isolated and individually
tested against the original test specification.
The individual amplifier units within the shelf have a green LED showing through a hole in their piggy-
back alarm board, which is illuminated if the unit is working correctly. If an amplifier is suspect, check
the DC 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.
6.1.3 Downlink
Confirm that there is a signal at the expected frequency and strength from the base station. If this is
not present then the fault may lay outside the system. To confirm this, inject a downlink frequency
signal from a known source at the Downlink input and check for the expected RF output.