LESSON 2
TELEPHONE AND TELEGRAPH COMMUNICATION
SCOPE........................................................................... Simple telephone circuits; characteristics of telephones
and connecting lines; function of telephone
switchboards; principles of telegraph transmission.
CREDIT HOURS ........................................................... 1
TEXT ASSIGNMENT ................................................... Attached Memorandum, para 2-1 thru 2-6
MATERIALS REQUIRED............................................. None
SUGGESTIONS............................................................. None
LESSON OBJECTIVES
When you have completed this lesson, you should:
1. Know that a telephone communication system is made up of smaller subsystems or circuit components.
2. Know that a switchboard provides interconnection capability between subsystems and circuit components.
3. Be able to compare the characteristics of manual and dial telephone systems.
4. Be able to compare common-battery and local-battery telephone systems.
5. Know that ac telegraph devices permit information from dc telegraph signals to be transmitted over a
telephone circuit.
ATTACHED MEMORANDUM
2-1. THE TELEPHONE SET
Every telephone set contains three basic elements: a transmitter (microphone), a receiver (earpiece), and a
sounder (bell or buzzer). The microphone generates the voice currents, and the earpiece converts the voice
currents back to sound waves. These two elements therefore operate on electromagnetic principles. The bell or
buzzer signals the desired party. Some telephones are equipped with a handcranked generator to develop
signaling voltage.
2-2. TELEPHONE SYSTEMS
a. A Simple Telephone System. A simple telephone system consists of two telephone sets connected by a
pair of wires. Voice currents developed in the microphone of one telephone set travel over the connecting wire
and excite the earpiece of the distant telephone set. The sound reproduced by the earpiece conveys the message to
the listener. The return circuit uses an identical
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