A telephone subset consists of an earpiece, which we may call the receiver; the mouthpiece, which we may call the transmitter; and some control circuitry in the telephone cradle-stand. Figure 5.3 illustrates a telephone subset connected all the way through its subscriber loop to the local serving exchange. The control circuits are aptly shown.
The hook-switch in Figure 5.3 (there are two) are the two little "knobs" that pop up out of the cradle when the subset is lifted from its cradle. When the subset is replaced in its cradle, these knobs are depressed. This illustrates the "on-hook" and "off-hook" functions described earlier. The "dial-switch" represents the function of the telephone dial. It simply closes and opens (i.e., makes contact, breaks contact). If a 1 is dialed, there is a single break and make (the loop is opened and the loop is closed). When the "loop is closed,"
current flows; when open, current stops flowing. If, for instance, a 5 is dialed, there will be five break-and-make operations which represent the digit 5.
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