Analog Subscriber Lines [45

Figure 1.4-3 shows a connection between two subscribers served by an analog local exchange. The subscriber lines (SLs) and the path (P) across the exchange are two-wire circuits.

The power of an electrical signal decreases as it propagates along the circuit. This attenuation becomes more severe with increasing circuit length.

The characteristics of microphones and receivers are such that a listener receives a sufficiently strong acoustical signal when at least 1% of the electrical signal power produced by the talker's microphone reaches the listener's receiver. This corresponds to the attenuation in a circuit of about 15 miles. Most subscriber


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