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BASIC OF TELEPHONE

3. TYPES OF TELEPHONES

There are three types of telephone: dial telephones and pushbutton tele-

phones that are used on analog lines, and digital telephones that are used

on digital lines.

In this section, let’s learn about these types of telephones.

3.1

Dial Telephones

The type of telephone having a dial as explained earlier in section 2.5 is a

dial telephone.

3.2

Pushbutton Telephones

Pushbutton telephones differ from telephones that are operated by turning

a dial in that buttons are pushed to output dialing signals.

Pushbutton telephones have 12 buttons and have an oscillator inside to

generate seven different frequencies. For example, if you push button 1,

two frequency currents, 697 Hz and 1209 Hz, are sent simultaneously. This

is called

(Dual Tone Multi Frequency), and dialing using this

DTMF is called “tone dial” due to the fact that numbers are dialed by this

tone. Dialing is also referred to as PB (Push Button) due to the fact that

buttons are pushed.

The exchange distinguishes numbers by this DTMF.

Of these 12 buttons, the * and # buttons are special buttons, and are used

for selecting various handy communications services.

Fig. 1-12 Pushbutton Telephone

697Hz

1209Hz

Mixed signals

(PB signal)

697Hz

770Hz

852Hz

941Hz

1209Hz

1477Hz

1336Hz