Figure 5-9.--Operation of sound-powered units.

armature to bend in the opposite direction. This action

armature is repelled by the north pole and attracted by

reduces the air gap between the armature and the north

the south pole. As the direction of the current in the

receiver reverses, the polarity of the armature reverses.

pole. The reluctance between the armature and the upper

north pole is decreased and the lines of force are

The position of the armature in the air gap reverses,

forcing the diaphragm inward. The diaphragm of the

reestablished through the armature, this time in the

opposite direction.

receiver unit vibrates in unison with the diaphragm of

the transmitter unit and generates corresponding sound

As the sound waves strike the diaphragm, they

waves in the receiver unit.

cause the diaphragm to vibrate back and forth. The

LOADING HANDSET.-- Handsets are designed

armature bends first to one side and then to the other,

to give maximum operating efficiency when used in a

causing an alternating polarizing flux to pass through it,

first in one direction and then the other. These lines of

1-to-1 ratio. The number of handsets operating in

force passing through the armature will vary in strength

parallel should in no case exceed four. Where more than

four are deemed necessary from an operational

and direction, depending upon the vibrations of the

diaphragm. This action induces an electromotive force

standpoint, the communication should be by

(emf) of varying direction and magnitude; that is, an

sound-powered headset-chestsets. To maintain the

alternating voltage in the coil. This alternating voltage

overall efficiency of the circuit, handset buttons should

has a frequency and waveform of the sound wave

not be taped down for convenience, as this may overload

striking the diaphragm.

the lines. When using the handset, you should speak in

a loud, clear voice. The power of the transmitter is

Principles of Operation of the Receiver

generated by the voice, and while shouting is not

Unit.-- The sound-powered receiver unit reverses the

necessary, the louder the speech, the louder the message

transmission process. The alternating voltage generated

is heard in the distant handset. When a handset is not

in a transmitter unit is impressed upon the receiver coil,

in use, it should be stowed in its holder or stowage

which surrounds the armature of the receiver unit. The

cabinet.

resultant current through the coil magnetizes the

armature with alternating polarity. An induced voltage

Sound-Powered Headset-ChestSets

in the coil of the transmitter unit (fig. 5-9, view A) causes

a current to flow in the coil of the receiver unit (fig. 5-9,

vie w B), magnetizing the free end of the armature

Sound-powered headset-chestsets are designed for

arbitrarily with north polarity. The free end of the

general use and for use with sound-powered telephone

Figure 5-9.--Operation of sound-powered units.

5-11