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Chapter 3. Coaxial Cable > Noise Environment

3.7. Noise Environment

Transmission characteristics have been extensively field-tested for the purpose of implementing cable modem and other digital services [5]. In the reverse channel frequency band between 5 and 40 MHz, ingress noise level is relatively high. It was found that ingress spectral contents are confined to narrow frequency ranges. Sources of ingress include short-wave broadcasts, HAM band transmission, and CB traffic. In general, the spectral energy density decreases as frequency increases. Figure 3.11 shows one example of many field-collected measurements. There are seven visible plots representing minimum, first decile, first quartile, third quartile, ninth decile, 99th level, and maximum, respectively, in Figure 3.11. In real time, many of these noise peaks show noticeable amplitude vibration. This might be related to the analog modulation nature of these interference signals.

Figure 3.11. Ingress Noise Measurements



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