Cisco Systems UBR7225VXR specifications Vector Signal Analyzer Plot of Upstream Data Burst

Chapter 4 Connecting the Cisco uBR7225VXR Router to the Cable Headend

Measuring the Upstream RF Signal

Figure 4-35 Vector Signal Analyzer Plot of Upstream Data Burst

The upper graph in Figure 4-35represents the frequency domain and the lower graph represents the time domain.

In the time domain, the channel power of the preamble of a digital upstream signal is not spread across the entire channel. However, the channel power of the remainder of the digital transmission is spread across the entire channel. Even though it may not seem so, the total channel power across both the preamble and the subsequent data segment remains constant.

b.Narrow the view on your vector signal analyzer to display only the preamble of the digital data signal in both the frequency domain and time domain.

The upper display in Figure 4-36is a plot of only the preamble portion of the digital signal in Figure 4-35. Notice how the amplitude of the signal experiences many “peaks” and “valleys.” When you are measuring the preamble power using the zero-span method, be sure that you measure the actual signal energy (a peak), rather than accidentally measuring the power level of a valley in the preamble.

	Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
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