Juniper-networks G10 CMTS Manual de usuario descargar pdf (Pagina 152)

Downstream RF Measurement in Spectrum Analyzer Mode

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JUNOSg 3.0 G10 CMTS Hardware Guide

136

5. Press the SPAN key and enter 6 MHz.

6. Press the BW key and turn video averaging on by selecting VID AVG ON. The default

number of averages is 100. You can change the number of averages by using the

numeric keypad.

7. Press the MKR FCTN key (marker function) and select MK NOISE ON. This sets the

spectrum analyzer to read out the power bandwidth, normalized to 1 Hz. The spectrum

analyzer display should be similar to the display in Figure 41.

8. The power shown on the display in Figure 41—shown in the top/right and

middle/left—is –19.12 dBmV, at 1 Hz. In order to obtain the power in the 6 MHz

channel, a correction factor is required. This correction factor equals

10 log(ChannelBW/measurementBW). In this case, 10 log (6x10^6/1) equals 67.78 dB.

Therefore, the actual downstream channel power equals (-19.12 dBmV+67.78 dBmV),

which equals 48.66 dBmV. Ensure that this power value is approximately equal to the

configured downstream power level, minus any attenuation between the HFC Connector

Module or SIM downstream port and the point at which your measurement is taken in

the cable plant. In this example, assume the attentuation between the CMTS and the

measurement point is approximately 13 dB. Therefore, the expected measured value

should be approximately 48 dBmV.

Figure 41: Downstream RF Signal (Spectrum Analyzer Mode)

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Juniper-networks G10 CMTS Manual de usuario Pagina 152