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Measuring System Performance: Modem Carrier-to-Noise Measurements

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as trigger level threshold, sweep time, measurement bandwidth, video

bandwidth, and resolution bandwidth. You must also be proficient at RF

signal evaluation in the time-domain mode (versus the standard frequency

domain mode).

To overcome the confusing test equipment set-up process, Acterna has

introduced a new instrument feature that allows technicians at all skill levels

to perform accurate return-path cable modem C/N measurements.

Why Measure Cable Modem C/N?

The modem C/N of the return cable plant can determine whether the return

network is capable of reliably carrying cable modem traffic. The US DOCSIS

standard states that the C/N for upstream (return) digital signal types is 15

dB for QPSK and 25 dB for QAM-16. Although most QPSK and QAM-16

signals are robust enough to transmit through noisier return path

environments, complying with the DOCSIS C/N standard will ensure that

cable modems will reliably operate on the return network.

Measuring Modem Carrier-to-Noise

From the Sweep & Spectrum tab in the Navigator, select the Modem C/N

icon. The screen shown in Fig. 6-7 will appear

Fig. 6-7 The Modem C/N main screen

There are four items that you can set up for the measurement: Center

Frequency, Pre-Amp state, Low Pass Filter State, and Measurement

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