User's Manual

P B L Tunnel Units 1 & 2
Maintenance Handbook
H/book Number:-60-056100HBKMFCC
Issue No:-2
Date:-04/01/2006
Page:-
11 of 63
2. OVERVIEW/SYSTEM DESCRIPTION
The AFL Fibre feed Amplifier for the Pasadena Blue line project is a 2 way on-band RF
amplifier. The primary application is as an interface between the fibre optical link from UNIT
ONE (Port 3 Downlink/Port 4 Uplink) and the tunnel antenna/leaky feeder system(Ports J3
and J4). There are two units, one designated ‘UNIT 1’, which is a fibre Tx or Rx with an
associated bandpass filter for each RF path, and ‘UNIT 2’ (a Bi-Directional amplifier) for the
frequencies in the 483-486MHz range.
Each unit is housed in an environmentally protected IP65 steel wall-mount case. Handles are
provided for carrying the unit and the door is fitted with locks. The unit interfaces with ‘N’
type female connectors for RF connections and heavy duty connectors for routing of AC
power supply input and alarm output wiring. Cable glands are provided for routing of the
Fibre optic cable in to the units.
The downlink signal path is as follows: The signal is received by a fibre optic receiver
located in unit 1 it is then split in to two paths using bandpass filtering for the frequencies
required. One downlink path is contained in unit 1 the other in unit 2. To provide the
required gain to reach the required signal levels, low-noise amplifiers (LNA’s) are used in
each path, these being followed by power amplifier modules to provide the required
intermodulation performance. The paths are then recombined using bandpass filtering (in unit
2) and are fed to the radiating cable. Gain adjustment is available locally using switched
attenuators.
Similarly the uplink path is taken from the radiating cable and spilt into the two required
frequency bands. One uplink path is contained in unit 1 the other in unit 2, again to provide
the required gain to reach the required signal levels, low-noise amplifiers (LNA’s) are used in
each path, these being followed by power amplifier modules to provide the required
intermodulation performance. The paths are then recombined using bandpass filtering and are
fed to a fibre optic transmitter. Gain adjustment is available locally using switched
attenuators.
To provide adequate selectivity in the Downlink and Uplink paths, combline design
duplexers are used at the input and output ports.
Note that “Downlink” refers to the RF path from FO receiver to the leaky feeder port and that
“Uplink” refers to the RF path from the leaky feeder port to either the FO transmitter or off-
air antenna.