Telephone Set


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telephone set

[′tel·ə‚fōn ‚set]
(engineering acoustics)
An assembly including a telephone transmitter, a telephone receiver, and associated switching and signaling devices. Also known as telephone.

Telephone Set

 

the apparatus used in a telephone-communication system mainly to transmit and receive vocal information. A telephone set generally comprises a handset with a transmitter and receiver and a separate housing with a switch hook, dial, and ringer.

Figure 1. Simplified circuit illustrating the reduction of sidetone through the bridge method: (T1) and (T2) terminals for the subscriber line, (SH) switch hook in position to receive a call, (R) ringer, (D) dial, (IC) impulse contact of the dial, (Rc) receiver, (Tr) transformer, (M) transmitter, (2) impedance of the balancing network, and (C1) and (C2) contacts of the switch hook

The design of the set’s housing depends on whether the central office providing service is manual or automatic. In a telephone set served by a manual office, a magneto is used to send calling signals to the office or directly to another telephone set; alternatively, calling signals can be sent to the office upon the lifting of the handset. In a set served by an automatic office, calling signals are sent by means of a key pulser or a dial. The telephone set is shifted from a state of readiness to receive ringing signals to a state wherein a conversation can be carried on, and vice versa, by means of the switch hook. The subscriber is alerted to an incoming call by the electric ringer or, more rarely, by a lamp.

The most important components of the handset are the receiver and the transmitter; for convenience, these components are combined in a single structural unit. Depending on the method of supplying power to the transmitter, telephone sets are classified as central-battery, in which the battery is usually installed at the central office, or local-battery, in which a galvanic cell is located either inside or nearby the set’s housing. A distinction is also made between anti-sidetone telephone sets and side-tone sets, now virtually obsolete (sidetone being the sound of the speaker’s own voice as heard in the receiver). Depending on the method of reducing effect, anti-sidetone sets are further subdivided into bridge and compensation types.

When a telephone set of the bridge type (Figure 1), is in the “talking” state, the transformer windings of the transmitter circuit, the balancing network, and the subscriber’s line form a bridge circuit with the transmitter connected across the diagonal; the sidetone is reduced by making the impedance of the balancing network equal to the line impedance (by fitting resistors and capacitors of the balancing network). Circuits of the compensation type differ from bridge circuits in having a connection between the receiver and the other circuits of the telephone set through a varistor.

Telephone sets are available in the form of table, wall, integrated (a combination of table and wall), and portable models.

The different types of telephone sets include pay stations; sets with a transistor amplifier in the transmitter and/or receiver circuits, used when the transmitting or receiving signal is below a certain level; loudspeaker telephone sets; telephone headsets, used in radiotelephone communications; and videotelephone sets.

REFERENCES

Gubrenko, I. M., and E. V. Kuchumov. Telefonnye apparaty ATS. Moscow, 1968.
Gubrenko, I. M., and E. V. Kuchumov. Telefonnye apparaty, ispolzuemye v sel’skoisviazi. Moscow, 1969.

I. M. GUBRENKO and E. V. KUCHUMOV

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