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Measuring the Upstream RF Signal
Measuring the Upstream RF Signal
You can use a spectrum analyzer to measure the upstream signal from one or more remote cable modems
in a two-way data cable network. Performing this procedure can help alert you to potential problems in
your cable network's upstream configuration before a problem occurs. This helps to avoid trying to solve
a problem after a remote cable modem has experienced a failure in service. This procedure is referred to
as the "zero-span" method.
Measuring the Upstream RF Signal Using a Spectrum Analyzer
This procedure is designed to help you accurately measure an upstream RF signal where no adjacent
channels are in use. To measure an upstream RF signal with active adjacent channels, refer to the
the Zero-Span Method with Adjacent Upstream Channels" section on page
Refer to the user guide that accompanied your spectrum analyzer to determine the exact steps required
Note
to use your analyzer to perform these measurements.
Connect the spectrum analyzer to the upstream signal from your cable network.
Step 1
Turn the power switch on the spectrum analyzer to the on position.
Step 2
Set the spectrum analyzer to view the upstream RF signal with a center frequency matching the actual
Step 3
upstream center frequency defined in your Cisco uBR7225VXR router configuration file.
Set the spectrum analyzer's span to 0 MHz.
Step 4
You can view the configuration file for your Cisco uBR7225VXR router by using the
Note
show controller cable slot/upstream/port command, available in Cisco IOS Release 11.3(6)NA or later
releases and Cisco IOS Release 12.0(5)T1 or later releases. For example, if you wanted to view the
center frequency of port 0 on a cable interface card in slot 3, you would enter the
show controller cable 3/0 command.
If you have assigned spectrum groups in your configuration file, use the show cable hop command to
display the current upstream center frequency for each cable interface.
Set both the resolution bandwidth and the video bandwidth on the spectrum analyzer to 3 MHz and the
Step 5
sweep rate to 20 microseconds. Provided there is a large amount of activity on your upstream channel,
the spectrum analyzer should display a signal similar to the one shown in
Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
4-22
Chapter 4
Connecting the Cisco uBR7225VXR Router to the Cable Headend
"Using
4-28.
Figure
4-26.
OL-17309-01
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Troubleshooting
