Cisco GS7000 Installation And Operation Manual page 210

Appendix B
Enhanced Digital Return Multiplexing Applications
The amplitude of the received test signals at the output of the reverse optical
receiver in the headend or hub may be measured and monitored using the
following:
Spectrum analyzer (when using a CW generator for test signals)

Signal level meter (when using a CW generator for test signals)

Reverse sweep receiver (when using a reverse sweep transmitter for test signal)

The variance in relative amplitude of the received signal from desired (reference)
may be relayed to the field technician via the following:
Radio (by a second technician in the headend/hub who is monitoring a spectrum

analyzer or signal level meter)
A dedicated forward TV channel, whose associated modulator has its video

input being generated by a video camera focused on the spectrum analyzer
display
An associated forward data carrier (if using a particular type of reverse sweep

system)
If a portable reverse sweep generator with built-in forward data receiver is used to
generate the reverse test signals, only one technician is required to perform the
balancing. This type of system is becoming increasingly popular due to its ease of
use.
In this case, the sweep system includes a combination reverse sweep receiver and
forward data transmitter, which is located in the headend/hub. The frequency
response characteristics of the received sweep signal (including relative amplitude
and tilt) are converted by the headend sweep receiver to a data format, and
transmitted in the forward RF path as a data carrier (by combining it into the
forward headend combiner). The portable sweep generator/data receiver that is
injecting the test signal into the RF launch amplifier's reverse path in the field is
simultaneously receiving the incoming data carrier via the forward RF path. The
incoming data is converted back to a sweep display that represents what is being
received by the headend unit.
Reverse Balancing and Alignment Procedure
Overview
Digital Return technology is designed to have a constant link gain, regardless of the
length of fiber or amount of passive optical loss in the link. That is, if the RF signal
amplitude of all ports in all nodes is set to a constant value, the signal level at the
output of the receiver will be balanced automatically to a constant power level.
Minor differences in levels can be trimmed out at the receiver with no penalty to link
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