Cisco UBR7225VXR Hardware Installation Manual page 106

Measuring the Upstream RF Signal
Figure 4-37
Switch your vector signal analyzer over to quaternary phase shift keying (QPSK) demodulation
d.
mode. Your vector signal analyzer will display a set of screens similar to those in
Figure 4-38
Figure
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
Vector Signal Analyzer Plot of Upstream Data Burst (Preamble Only)—QPSK
Demodulation Mode
displays the QPSK demodulation information for the same upstream signal as in
4-37. However, there are some notable differences in the information presented. For example,
Chapter 4 Connecting the Cisco uBR7225VXR Router to the Cable Headend
Figure 4-38.
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