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Set the Downstream Center Frequency
Configuring Cisco uBR7246 Universal Broadband Router Features VC-139
Note The default values for the commands used in these configuration steps are, in most cases,
adequate to configure the Cisco uBR7246.
Set the Downstream Center Frequency
You need to set the downstream frequency of your RF output to comply with the expected input
frequency of your upconverter. To do this, enter the fixed center frequency of the downstream RF
carrier for a downstream port.
Downstream frequency is an information-only command that should reflect the digital carrier
frequency, which is the center frequency of the downstream RF carrier (the channel) for that
downstream port. The configuration controlling the digital carrier frequency is done in the IF-to-RF
upconverter that must be installed in the downstream path from the Cisco uBR7246. Refer to the
upconverter’s manufacturer’s instructions for information about configuring the upconverter.
The digital carrier frequency is specified to be the center of a 6.0 MHz channel. For example, EIA
channel 95 spans 90.000 to 96.000 MHz. The center frequency is 93.000 MHz, which is the digital
carrier frequency that should be configured as the downstream frequency.
Note The digital carrier frequency is not the same as the video carrier frequency. For EIA channel
95, the video carrier frequency is 91.250 MHz, which is 1.75 MHz below the center frequency.
Note This command currently has no effect on external upconverters; it is informational only.
To set the downstream center frequency, use the following command in cable interface configuration
mode:
Validation Tips
To verify the current value of the center frequency, enter the show controllers cable command for
the downstream port that you have just configured:
• If the center frequency is fixed, the actual frequency will be displayed:
router# show controllers cable 6/0 downstream
Cable6/0 Downstream is up
Frequency=96000000, Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps
FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=4
• If the center frequency is not fixed, the frequency will show that it is not set:
router# show controllers cable 6/0 downstream
Cable6/0 Downstream is up
Frequency is not set. Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps
FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=4
Command Purpose
cable downstream frequency down-freq-hz Enter the fixed center frequency for your downstream
RF carrier in Hz.