Telephone - Telephone Set

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1. CARBON TRANSMITTER made up of 2 metal plates (electrodes) with carbon granules inbetween.

one metal plate is thin diaphragm that takes variations in pressurecaused by sound waves and transmits these to the carbon granules.

electrode conduct electricity that flows through the carbon.

resultant current varies with the sound-wave pressure applied to thetransmitter .

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2. ELECTRET TRANSMITTER composed of thin disk of metal-coated plastic and a thicker, hollowmetal disk.

plastic disk is electrically-charged and so electric field is created inthe space where disks do not touch.

callers voice causes the plastic disk to vibrate changing the electricfield intensity between them.

electric field variations are interpreted as electric current variationswhich then travels through telephone lines

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made from flat ring of magnetic material with short cuff of the samematerial attached to the rings outer rim.

underneath the magnetic ring and inside the magnetic cuff is a coil ofwire through which electric current representing the sounds from distant

telephone flows.

magnet a thin diaphragm of magnetic material is suspended from theinside edges of the magnetic ring so that it is positioned between themagnet and the coil.

magnetic field created by the magnet changes with the current in the coiland makes the diaphragm vibrate.

vibrating diaphragm creates sound waves that replicates the sounds thatwere transformed into electricity by the other persons transmitter.

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switches on the telephone set when operated

1. ON-HOOK CONDITION

handset rests on its cradle if the telephone is idle or inactive. switch-hook is open so no DC current flows through the line.

2. OFF-HOOK CONDITION

handset is lifted off from its cradle. switch- hook contact is closed so DC current flows from thecentral office through the telephone set and through a relay coil atthe central office.

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SIDETONE

small amount of the transmitted signal fed to the receiver of thetaking phone.

VARISTOR

provides automatic adjustment of the sidetone level for telephoneset installations as variations in loop current due to the differentlength of the local loops.

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informs the subscriber of incoming telephone call.

responds to special frequency of electricity sent in response to therequest for that telephone number.

a.k.a alerter.

early ringers use metallic gong bell struck by metal clapper

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where subscribers input telephone numbers using: rotary dialer or bypush-button dialer.

1. PULSE DIALING

2. TONE DIALING

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1. PULSE DIALING a.k.a DIAL PULSING orROTARY DIALING

numerals 1 to 9, followed by zero are placed in a circle behind round

holes in a movable plate.

user places finger in the hole corresponding to the desired digit androtates the movable plate clockwise until the users finger reach stop, thenuser removes the finger.

this results to a number of dial pulses in the electrical current flowingbetween the telephone set and the exchange. Equipment at the exchangecounts these pulses to determine the number being called.

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2. TONE DIALING

uses two tones or two frequencies to represent a single digit.

a.k.a Dual-Tone Multi-Frequency (DTMF) dialing.

numerals 1 to 9 each represents one of the twelve availablepushbuttons in the keypad.

central office is equipped with code receiver that interpretsthe numbers dialed according to the DTMF tones it receives

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For touch tone dialing: 0.25 sec to 0.5 sec /pulseplus 0.25 to 0.5 sec inter- digit time.

Example:How long does it take to dial 345-0238 in seconds using touch-tonedialing?

Answer:tt = 7(0.25)+6(0.25)

tt = 3.25 sec

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TOUCH-TONE MULTI- FREQUENCY CODE

9

32

D

C

5

* 00

4B6

A

7 8

#

697 Hz

770 Hz

852 Hz

941 Hz

1209 Hz 1336 Hz 1477 Hz 1633 Hz

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MULTI-FREQUENCY CODE

DIGIT TOUCH-TONE (Hz)1 697 + 1209

2 697 + 1336

3 697 + 1447

4 770 + 1209

5 770 + 1336

6 770 + 1447

7 852 + 1209

8 852 + 1336

9 852 + 1447

0 941 {+ 1336