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Measuring the Upstream RF Signal
The 4.25 dB decrease in amplitude is due to a combination of half of the channel bandwidth (3 dB) and
Note
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
Narrow the resolution bandwidth from 1 MHz to 100 kHz and increase the video bandwidth to 3 MHz,
Step 9
still retaining the 60 microseconds sweep time. Your spectrum analyzer should display a signal similar
to
Figure
Figure 4-43
Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
4-36
Preamble with Decreased Amplitude and Condensed Sweep Time
4-43.
Very Narrow Resolution Bandwidth Limits Range of Spectrum Analysis
Chapter 4
Connecting the Cisco uBR7225VXR Router to the Cable Headend
OL-17309-01
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Troubleshooting
