The Telephone Essay Research Paper The TelephoneAbout

The Telephone Essay, Research Paper

The Telephone

About 100 years ago, Alexander Graham Bell invented the telephone by

accident with his assistant Mr. Watson. Over many years, the modern version of

the telephone makes the one that Bell invented look like a piece of junk.

Developments in tone dialing, call tracing, music on hold, and electronic

ringers have greatly changed the telephone.

This marvelous invention allows us to communicate with the entire globe

24 hours a day just by punching in a simple telephone number. It is the most

used piece of electronic apparatus in the world. It is probably one of the most

easy to use electronics available too. All you have to do is pick up the

receiver, listen for the tone, and then select a number using either tone or

pulsing dial.

A telephone can be separated into two main categories: there is the tone

(touch tone) or the older rotary dial (pulse) telephones. Then you can divide

those into other categories such as business line (multi — line) or home line

(single line). You can also have many other types of phones: there are those

that hang on the wall, on the desk, etc.

THE HANDSET

No matter what kind of telephone you own, there has to be some device

that allows you to talk to and listen to. This device is called the handset. The

handset is usually made out of plastic and inside it are two main components:

the transmitter and the receiver.

THE TRANSMITTER

It is the job of the transmitter to turn the air pressure created by

your sound waves to electrical signals so they can be sent to the other

telephone. The waves hit a thin skin called the diaphragm that is physically

connected to a reservoir of carbon granules. When the pressure hits the

diaphragm, it shakes up the carbon granules. Then the carbon expands and

contracts, depending on what force is exerted. At two points on the outer shell

of the reservoir of the carbon are two outlets of electricity from the talk

battery. By applying voltage, a current is made and is passed along the lines to

the waiting telephone. At the other end the current is transformed back to

speech.

THE RECEIVER

The receiver turns an ever varying current back to speech. A permanently

magnetized soft iron core is covered in many turns of very fine wire. Through

the wire, the electrical current is applied. The currents attract and repel an

iron diaphragm. By the vibrating actions the diaphragm does, a different

pressure is created and these pressures are translated by ear into intelligible

speech.

TELEPHONE NETWORKS

If you have ever opened up a phone (do not try this at home, you might

screw it up) you will probably see a PC (printed circuit) board. The board

contains the needed electronics for the phone to work properly. In older models

of a working telephone, this board may look like an electronic box. This board

is called the telephone network.

The telephone network’s function is to provide all the necessary

components and termination points (screw on or push on terminals). The

components and the termination points connect and match the impedance of a

handset (transmitter and receiver) to a two — wire telephone circuit.

Every component in the telephone has to be connected to the PC board.

Usually, the board is the most reliable component inside the phone. All the

delicate components are securely sealed by a metal enclosure. The PC board is a

very fragile object and can be broken easily. If you look closely, you can see

wires poking out of the board. The wires are soldered to the terminal legs. If

you break one of those wires, man are you dead!

TELEPHONE HOOK SWITCH

Every time you talk over a line, you always need to disconnect. The most

simple thing to do is to let the handset sit down. While sitting down, the

handset can give force to a spring loaded operating arm, which is connected to a

number of switch contacts. When this happens, the phone disconnects.

THE PHONE RINGER

Once a call has been dialed through, the telephone of the person being

called must be given some kind of signal to let him/her know that he/she has

been called. This is when the telephone rings. This type of signal is generated

using an alternating current somewhere between 90 to 220 V with a frequency of

30 Hz.

But what if you have 5 or 6 phones connected on a party line. How can

you signal one telephone to ring. The answer is by frequency selection. Older

telephones had a different capacitor and ringer coil impedance values. It was

these small differences that made the bell select one frequency.

For example, if you have 5 telephones on one party line. If a call came

through for line 1, the central board would send 10 Hz (this is a guess) signal

to the party line. Line 1 would ring and all the others would remain quiet. If

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