Juniper G10 CMTS, Hardware Manual

Page: 152 / 210

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)