Cisco Systems UBR7225VXR specifications OL-17309-02

Chapter 4 Connecting the Cisco uBR7225VXR Router to the Cable Headend

Measuring the Upstream RF Signal

Figure 4-37 Vector Signal Analyzer Plot of Upstream Data Burst (Preamble Only)—QPSK Demodulation Mode

d.Switch your vector signal analyzer over to quaternary phase shift keying (QPSK) demodulation mode. Your vector signal analyzer will display a set of screens similar to those in Figure 4-38.

Figure 4-38displays the QPSK demodulation information for the same upstream signal as in Figure 4-37. However, there are some notable differences in the information presented. For example, notice that the constellation and transition graphs (top and bottom left) both indicate only two of the four QPSK data points handling any bits. Because this graph is covering only the preamble of the data transmission, you get to see only a portion of the whole signal performance. (If you were to view the entire signal transmission in this mode, all four QPSK data points would display bits.)

	Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
4-32	OL-17309-02