User Manual

Fibre Optic Master and Remote Site
User Handbook
Document Number: 60-212701HBK - Issue No. 1 Page 43 of 50
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 master site BTS input and check for output at the remote site
feeder output.
If a signal is not received at the output it will be necessary to follow the downlink path through the
system to find a point at which the signal is lost. The expected downlink output for the given input can
be found in the end-to-end test specification.
6.1.4 Uplink
Testing the uplink involves a similar procedure to the downlink except that the frequencies used are
those transmitted by the mobile equipment.
6.1.5 Fibre Optics
The Fibre Optic transmitters and receivers both have two LED status indicators, one on each module
showing DC power and the other indicating ‘Laser On’ for the transmitter, and ‘Carrier Being
Received’ for the receiver. Assuming that all of the indicators are illuminated, it will be necessary to
check the RF inputs and outputs to the fibre optic units.
Typically the input to transmitter units will be at a level of between -30 and -15 dBm. The RF gain of a
pair (TX to RX) units is factory set to give a 0dB gain, but this is with a short, low loss fibre. In
determining the performance of the link, the insertion loss of the fibre and any power splitters fitted
must be considered. A general rule of thumb figure would be around 0.5 - 1.5dB loss per Kilometre.
6.1.7 Checking service
Following the repair of any part of the system it is recommended that a full end-to-end test is carried
out in accordance with the test specification and that the coverage is checked by survey.
It is important to bear in mind that the system includes a radiating cable network and base stations
that may be faulty or may have been damaged.
6.1.8 Fault repair
Once a faulty component has been identified, a decision must be made on the appropriate course to
carry out a repair. A competent engineer can quickly remedy typical faults such as faulty connections
or cables. The exceptions to this are cable assemblies connecting bandpass filter assemblies that are
manufactured to critical lengths to maintain a 50-ohm system.
Care should be taken when replacing cables or connectors to ensure that items are of the correct
specification. The repair of component modules such as amplifiers and bandpass filters will not
usually be possible in the field, as they frequently require specialist knowledge and test equipment to
ensure correct operation. It is recommended that items of this type are replaced with a spare unit and
the faulty unit returned to AFL for repair.