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572<br />

Wire and Wireless Communication Applications Chap. 8<br />

Telephone set<br />

On hook<br />

Earphone<br />

Dial pulser<br />

Off hook<br />

Switchhook<br />

Carbon<br />

microphone<br />

On hook<br />

Off hook<br />

Ringer<br />

Twisted-pair telephone line to subscriber<br />

Tip (green wire)<br />

Local telephone central office<br />

A<br />

Tip (green wire)<br />

90 V, 20 Hz<br />

Ring<br />

voltage<br />

generator<br />

200 200<br />

Line<br />

connected<br />

200 by circuit<br />

200<br />

switch<br />

48 V 48 V<br />

+ +<br />

90 V, 20 Hz<br />

Ring<br />

voltage<br />

generator<br />

Ring (red wire)<br />

B<br />

Twisted-pair telephone line to subscriber<br />

Ring (red wire)<br />

On hook<br />

Telephone set<br />

Off hook<br />

Dial pulser<br />

Earphone<br />

Ringer<br />

On hook<br />

Off hook<br />

Switchhook<br />

Carbon<br />

microphone<br />

Figure 8–2<br />

Local analog telephone system (simplified).

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