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Chapter 3 Balancing and Setup
68
Balancing the Reverse Path
This section covers reverse RF amplifier cascade balancing. Balancing refers to the
process of individually aligning reverse amplifier station gain and tilt characteristics
to achieve reverse amplifier cascades that have optimum, repeatable transmission
characteristics.
process of individually aligning reverse amplifier station gain and tilt characteristics
to achieve reverse amplifier cascades that have optimum, repeatable transmission
characteristics.
There are a variety of test equipment combinations that enable proper balancing of
the reverse path. Regardless of the type of equipment used, the balancing process is
fundamentally the same.
the reverse path. Regardless of the type of equipment used, the balancing process is
fundamentally the same.
About Reverse Path Balancing
Balancing should be completed in the following order.
1 Balance the reverse fiber link, i.e., the path from the amplifier reverse optical
1 Balance the reverse fiber link, i.e., the path from the amplifier reverse optical
transmitter to the headend or hub reverse optical receiver.
2 Balance the individual reverse amplifier cascades that combine at the amplifier.
Start with the amplifier closest to the amplifier, and work from that point
outward towards the first reverse amplifier in each upstream cascade.
outward towards the first reverse amplifier in each upstream cascade.
Injection of Test Signal(s)
During the balancing process, a reverse RF test signal or signals of known amplitude
are injected into the reverse RF input path of the amplifier station prior to the reverse
amplification circuit. The injected signals are amplified and routed out the station
reverse RF output port in the upstream direction. The injected test signals pass
through any previously balanced amplifiers in the reverse cascade, as well as the
reverse fiber link, and arrive at the amplifier reverse optical receiver, which typically
is located in the headend or hub.
are injected into the reverse RF input path of the amplifier station prior to the reverse
amplification circuit. The injected signals are amplified and routed out the station
reverse RF output port in the upstream direction. The injected test signals pass
through any previously balanced amplifiers in the reverse cascade, as well as the
reverse fiber link, and arrive at the amplifier reverse optical receiver, which typically
is located in the headend or hub.
Monitoring and Adjusting Received Amplitude and Tilt
The amplitude and tilt associated with the received signals are monitored at the
headend or hub at an RF test point on the output of the reverse optical receiver
associated with the particular amplifier. The received amplitude and tilt of the test
signals are compared to the desired (reference value) amplitude and tilt. Any
deviations from reference value amplitude or tilt are then minimized by altering the
(dB) value of the output pad or equalizer in the amplifier being balanced. This
process is completed for each amplifier in the reverse cascade, working outward from
the amplifier.
headend or hub at an RF test point on the output of the reverse optical receiver
associated with the particular amplifier. The received amplitude and tilt of the test
signals are compared to the desired (reference value) amplitude and tilt. Any
deviations from reference value amplitude or tilt are then minimized by altering the
(dB) value of the output pad or equalizer in the amplifier being balanced. This
process is completed for each amplifier in the reverse cascade, working outward from
the amplifier.
Methods of Generating and Monitoring Test Signals
The reverse RF test signals to be injected into the reverse path of the amplifier being
balanced may be generated by the following.
balanced may be generated by the following.
Multiple CW signal (tone) generator