TELEPHONE SET SYSTEM BASIC ELECTRONIC TUTORIALS

HOW A TELEPHONE WORKS? WHAT YOU NEED TO KNOW ABOUT THE TELEPHONE

The telephone arrived as a practical instrument over a century ago in 1876, an outgrowth of experiments on a device to send multiple telegraph signals over a single wire. Alexander Graham Bell, a native of Scotland, while conducting electrical experiments spilled acid on his trousers.

His reaction, the now-famous “Mr. Watson, come here, I want you,” brought Thomas A. Watson on the run not only because of his employer‘s distress, but because the words had been carried by electricity into Watson’s room and reproduced clearly on his receiving set.


The simple instrument being tested on Court Street in Boston on March 10, 1876, wasn’t very practical (the acid was used in the system), but improvement followed so rapidly that putting into action Bell’s concept of a public telephone network-“this grand system . . . whereby a man in one part of the country may communicate by word of mouth with another in a distant place”-was well under way by January 1878, when the first commercial exchange was operated in New Haven. By 1907, one hotel alone (the Waldorf Astoria in New York City) had 1,120 telephones and processed 500,000 calls per year.

The American Telephone and Telegraph Company (AT&T) was incorporated in March 1885 to manage the explosive growth of the fledgling telephone network across the United States. Virtually since the beginning, AT&T worked as a legal, regulated monopoly. This means that AT&T was allowed to establish, maintain, and control a single, universal network across the country without any competition, as well as provide all telephone sets and switching equipment to the general public. The federal government regulated its policies, practices, and fees. This set the groundwork for the development of the most advanced and efficient telecommunications system in the world.


Telephones have simple appearance and operation yet it performs a surprising number of functions. The most important ones are:

1. It requests the use of the telephone system when the handset is lifted.
2. It indicates that the system is ready for use by receiving a tone, called the dial tone.
3. It sends the number of the telephone to be called to the system. This number is initiated by the caller when the number is pressed (or the dial is rotated in older telephones).
4. It indicates the state of a call in progress by receiving tones indicating the status (ringing, busy, etc.).
5. It indicates an incoming call to the called telephone by ringing bells or other audible tones.
6. It changes speech of a calling party to electrical signals for transmission to a distant party through the system. It changes electrical signals received from
a distant party to speech for the called party.
7. It automatically adjusts for changes in the power supplied to it.
8. It signals the system that a call is finished when a caller “hangs up’’ the handset.

Of course, for a telephone to be of any use, it must be connected to another telephone. In the very early days of telephony, the phones were simply wired together with no switching. As the number of phones increased this became impractical, so the local exchange or central office was established to handle the switching and other functions.