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Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
OL-17309-02
Chapter 4 Connecting the Cisco uBR7225VXR Router to the Cable Headend
Measuring the Upstream RF Signal
Note The 4.25 dB decrease in amplitude is due to a combination of half of the channel bandwidth (3 dB) and
an additional 1.25 dB decrease attributed to the digital channel filter mask, known as the “alpha.” The
value of alpha is 25 percent of an upstream DOCSIS channel’s width, and the peak signal energy spread
across the entire upstream channel width.
Figure 4-42 Preamble with Decreased Amplitude and Condensed Sweep Time
Step 9
Narrow the resolution bandwidth from 1 MHz to 100 kHz and increase the video bandwidth to 3 MHz,
still retaining the 60 microseconds sweep time. Your spectrum analyzer should display a signal similar
to Figure 4-43.
Figure 4-43 Very Narrow Resolution Bandwidth Limits Range of Spectrum Analysis