Handbook

Denver Channelised CE
User/Maintenance Handbook
Handbook Nō.-50-063708HBKM Issue No:-2
Date:-03/11/2003
Page:-
11 of 51
For better understanding of the system, the system diagram on page 23 should be consulted.
Downlink path
Duplex system signals in the Downlink path arriving at Base Antenna port 2 are first passed
to the Base side chassis and so through a duplexed bandpass filter to ensure good input
selectivity. This is then followed by a 31dB gain LNA to provide some amplification and a
switchable attenuator then allows up to 30dB of gain adjustment in 2dB steps.
From here signals are routed to the Downlink Channel chassis where a 2 way splitter is
followed by two three way splitters to provide six equal paths. One of these is terminated
with a 50ohm load and the remaining five each connect to a channel selectivity module. The
Downlink channel modules offer 15dB gain and have ALC circuitry to limit the module
output to -25dBm. This is ensure that the total output power may not become higher than the
specified level. The channel module outputs are taken to two three way combiners for
connection to a two way combiner which then routes signals out of the Downlink Channel
chassis and to the Tunnel side chassis.
The Downlink duplex channel frequencies factory set are:
457.050MHz
458.225MHz
457.850MHz
457.300MHz
457.775MHz
In the Tunnel side chassis a 21dB gain LNA is then followed by a 15dB gain LPA to drive a
23dB gain 20Watt Power Amplifier which provides the final stage of amplification. The
Power Amplifier is followed by a duplexed bandpass filter connecting to the Radiating cable
port 2.
The Downlink simplex channel, 452.850MHz, is received at Base Antenna port 1 and is
passed through a bandpass filter to provide selectivity. A 31dB gain LNA then provides
initial amplification and this is followed by a switchable attenuator giving up to 30dB of
gain adjustment in 2dB steps. An ALC attenuator is then fitted for muting the input of the
channel module when an Uplink path signal has been detected and is being amplified in that
direction. The channel module following the attenuator has 15dB of gain and has ALC
circuitry to limit the module output to -20dBm to limit the total output power to that
specified in case of an increase in off-air signal input. The channel module is followed by a
31dB gain LNA and then a 15dB gain 1Watt LPA. A bandpass filter after the LPA connects
to the Radiating cable port 1.
Uplink path
All Uplink channels enter the Bi-Directional Amplifier at Radiating Cable port 2 and pass to
the Tunnel side chassis where a duplexed bandpass filter routes the signals to the Uplink
input amplifier, a 31dB gain LNA. A switchable attenuator then gives up to 30dB of gain
adjustment in 2dB steps before signals connect to the Uplink Channel chassis.
In the Uplink Channel chassis, a 2 way splitter connects to two three way splitters to provide
six equal paths. One of these is unused and so is terminated with a 50ohm load. Four of the
remaining paths each connect to a channel selectivity module giving 15dB gain with an
ALC limited maximum output of -23dBm. The four module outputs then connect to a four
way combiner for routing to the Base side chassis. The last of the six paths is routed to the
Simplex chassis which will be described later in this section.