Cisco UBR7225VXR Hardware Installation Manual page 82

Measuring the Downstream RF Signal
Figure 4-6
Step 4 Set the input of the upconverter to a digital QAM signal and the output level to the manufacturer's
recommended settings. Typical output amplitudes range from +50 to +58 dBmV, although DOCSIS
specifies +61 dBmV.
Set the spectrum analyzer to view the RF signal at the center frequency you selected for your headend.
Step 5
In this example, the RF center frequency is 699 MHz. Set your span to 20 MHz. Finally, set your channel
spacing and your channel bandwidth to 6 MHz.
If the RF signal is causing an overload condition on the spectrum analyzer input, your analyzer might
display a signal similar to the one shown in
indicates a false reading.
Figure 4-7
If you add attenuation to the input to the spectrum analyzer you can correct the overload condition as
Step 6
shown in
Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
4-8
Overloaded Spectrum Analyzer Input
Measuring the RF Signal at the Upconverter Output—Overload Condition
Figure 4-8.
Chapter 4 Connecting the Cisco uBR7225VXR Router to the Cable Headend
Figure 4-7. The sloping of the lines at the sides of the signal
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