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Balancing the Reverse Path
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Balancing the Reverse Path
This section covers reverse RF amplifier cascade balancing. Balancing refers to the
process of individually aligning reverse amplifier gain and tilt characteristics to
achieve reverse amplifier cascades that have optimum, repeatable transmission
characteristics.
process of individually aligning reverse amplifier 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 line extender reverse optical
1 Balance the reverse fiber link, i.e., the path from the line extender reverse optical
transmitter to the headend or hub reverse optical receiver.
2 Balance the individual reverse amplifier cascades that combine at the node. Start
with the line extender closest to the node, and work from that point outward
towards the first reverse amplifier in each upstream cascade.
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 line extender 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 line extender in the reverse cascade, as well as the
reverse fiber link, and arrive at the node reverse optical receiver, which typically is
located in the headend or hub.
are injected into the reverse RF input path of the line extender 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 line extender in the reverse cascade, as well as the
reverse fiber link, and arrive at the node 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 node. 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 line extender being balanced. This
process is completed for each line extender in the reverse cascade, working outward
from the node.
headend or hub at an RF test point on the output of the reverse optical receiver
associated with the particular node. 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 line extender being balanced. This
process is completed for each line extender in the reverse cascade, working outward
from the node.