Cisco Systems UBR7225VXR specifications 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

	Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
4-36	OL-17309-02