Chapter 4 Connecting the Cisco uBR7225VXR Router to the Cable Headend
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
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 “Using the
Note Refer to the user guide that accompanied your spectrum analyzer to determine the exact steps required to use your analyzer to perform these measurements.
Step 1 Connect the spectrum analyzer to the upstream signal from your cable network.
Step 2 Turn the power switch on the spectrum analyzer to the on position.
Step 3 Set the spectrum analyzer to view the upstream RF signal with a center frequency matching the actual upstream center frequency defined in your Cisco uBR7225VXR router configuration file.
Step 4 Set the spectrum analyzer’s span to 0 MHz.
Note You can view the configuration file for your Cisco uBR7225VXR router by using the
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.
Step 5 Set both the resolution bandwidth and the video bandwidth on the spectrum analyzer to 3 MHz and the 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 Figure
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