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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
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.
DTMF
(Dual Tone Multi Frequency), and dialing using this
1209Hz
1336Hz
1 2
697Hz
4
5
770Hz
7
8
852Hz
0
941Hz
Fig. 1-12 Pushbutton Telephone
1477Hz
697Hz
3
1209Hz
6
9
Mixed signals
(PB signal)
BASIC OF TELEPHONE
1–11
1
2
3
4
5
6
ït
çi
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