User Manual

Fibre Optic Master and Remote Site
User Handbook
Document Number: 60-212701HBK - Issue No. 1 Page 22 of 50
4.2. Remote Uplink/Downlink Shelf (60-212802)
The Remote Uplink/Downlink Shelf is an 8U Rack mount shelf and provides two separate RF paths,
uplink and downlink with provision to vary the gain of either path using a switched variable (0 to 30dB)
attenuator, one in each path. Each path is also fitted with an Automatic Gain Control (AGC) circuit
which consists of two units, a detector/amplifier and an attenuator. Normally the attenuators in the
AGC circuit are at minimum attenuation. The detector/amplifier unit monitors the RF level being
delivered by the power amplifier, and when a certain threshold is reached it begins to increase the
value of the attenuator to limit the RF output to the (factory set) threshold; therefore overloading of the
amplifiers is avoided.
The downlink signal is received from the master site as an optical signal which is demodulated into an
RF signal. The RF signal is then passed through a bandpass filter (tuned to pass the downlink
bandwidth 502.4MHz to 502.8MHz) to reject out-of-band noise and then passes through the downlink
AGC attenuator and into the Downlink Switched Attenuator. From the Switched Attenuator the
Downlink signal passes through two low power amplifiers (1W, 15dB gain and 2W, 15dB gain) and
then exits 60-212802 to go to the 100W Linearised Amplifier (80-245101). After leaving 60-212802
the downlink signal re-enters 60-212802, passing through the downlink AGC detector and a second
bandpass filter before exiting the shelf via the D/L Output port
The uplink RF path enters 60-212802 at the U/L Input port and the signal passes through a bandpass
filter (tuned to pass the uplink bandwidth 505.4MHz to 505.8MHz) to reject out-of-band noise. After
the bandpass filter the signal passes through a 30dB Low Noise Amplifier and then into the uplink
Switched Attenuator followed by the uplink AGC attenuator. After the AGC attenuator the signal
passes through a second bandpass filter and then through a low power amplifier (1W, 37dB gain)
followed by the uplink AGC detector. From the AGC detector the uplink signal passes into a fibre optic
transmitter where the RF signal is modulated into an optical signal for transmission via fibre optic
cable to the master site.
All the amplifier modules in this shelf are alarmed and the summary terminates at the rear panel
mounted 9-way ‘D’ alarm connector.
4.2.1. 60-212802 Parts List (Major Components)
Component
Part
Component Part Description Qty Per
Assembly
02-010901 Bandpass Filter 3
02-011204 Bandpass Filter 1
10-000701 Switched Attenuator 0-30dB 0.25W 1
10-000801 Switched Attenuator 0-30dB 1W 1
11-007402 Low Noise Amplifier 1
11-007901 Low Power Amplifier (1W) 1
12-021801 Low Power Amplifier (1W) 1
12-021802 Low Power Amplifier (2W) 1
13-003011 DC-DC Converter 24V -12V 1
13-003301 Mains Filter (8 Amp) 1
17-001109 AGC Logarithmic Detector /Amplifier 1
17-001117 AGC Detector /Amplifier 1
17-001201 AGC Attenuator 2
20-001601 12V Relay Board 1
20-001602 24V Relay Board 1
20-005401 Fibre Optic Transmitter (2.7GHz) 1
20-005501 Fibre Optic Receiver (2.7GHz) 1
80-008901 12V Relay Assembly 1
93-510077 0R02 50W Resistor Aluminium Clad 2
94-100004 60A Dual Diode 1
96-300067 PSU 600W (24V 23A) 2
96-920026 Circuit Breaker 10A 1