Trilithic 720 DSP, Operation Manual

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Page IV-184
720 DSP Operation Manual
Business Services Meter
The forward band has a larger bandwidth,
typically several hundred MHz. The forward band
contains signals that are transmitted from the
MSO to the customer, such as analog and digital
TV channels and DOCSIS downstream.
Forward Spectrum
The return band is smaller than the forward
and varies in size from about 40 to 100 MHz.
The return band is for signals transmitted from
the customer back to the MSO. This is mainly
DOCSIS upstreams. While the signals in the
forward band are constant and easy to detect,
the signals in the return tend to be bursty. This
can cause issues while attempting to measure
signals in the return band.
Return Spectrum
The Return Spectrum menu on the DSP line of meters is a powerful tool to troubleshoot and fix
many issues in a typical cable TV system. It can be used to detect ingress and noise sources
that can be disruptive to the return band of the system. These issues may lead to cable
modem problems, causing a poor experience for the user. While the return spectrum is very
good at detecting continuous signals, it does not always catch bursty signals such as a cable
modem upstream channels. An upstream burst can be as short as 6.25 microseconds.
If there is enough upstream traffic, return spectrum may catch a full channel, or it may only
catch a single slice of the channel. All these factors make it very difficult to differentiate traffic
signal, noise, and ingress under the traffic.