Invention of Telephone

On March 10, 1876, in Boston, Massachusetts, Alexander Graham Bell invented the telephone. 

Oersted discovered that an electric current creates a magnetic field. But could a magnetic field create electricity? If so, a new source of power beckoned. And the principle of electromagnetism, if fully understood and applied, promised a new era of communication.

In 1821 Michael Faraday reversed Oersted's experiment. He got a weak current to flow in a wire revolving around a permanent magnet. In other words, a magnetic field caused or induced an electric current to flow in a nearby wire. In so doing, Faraday had built the world's first electric generator.

In 1830 the great American scientist Professor Joseph Henry transmitted the first practical electrical signal. Henry created the forerunner of the telegraph. In the demonstration, Henry first built an electromagnet by winding an iron bar with several feet of wire. A pivot-mounted steel bar sat next to the magnet. A bell, in turn, stood next to the bar. From the electromagnet, Henry strung a mile of wire around the inside of the classroom. He completed the circuit by connecting the ends of the wires to a battery. Guess what happened? The steel bar swung toward the magnet, of course, striking the bell at the same time. Breaking the connection released the bar and it was free to strike again.

In 1837 Samuel Morse invented the first workable telegraph, applied for its patent in 1838, and was finally granted it in 1848. . A quick key tap broke the circuit momentarily, transmitting a short pulse to a distant sounder, interpreted by an operator as a dot. A more lengthy break produced a dash.

Yet as the telegraph was perfected, man's thoughts turned to speech over a wire.

On June 2, 1875, Bell and Watson were testing the harmonic telegraph when Bell heard a sound come through the receiver. Instead of transmitting a pulse, which it had refused to do in any case, the telegraph passed on the sound of Watson plucking a tuned spring, one of many set at different pitches. How could that be? Their telegraph, like all others, turned current on and off. But in this instance, a contact screw was set too tightly, allowing current to run continuously, the essential element needed to transmit speech. Bell realized what happened and had Watson build a telephone the next day based on this discovery. 

The Watson-built telephone looked odd and acted strangely. Bellowing into the funnel caused a small disk or diaphragm at the bottom to move. This disk was, in turn, attached to a wire floating in an acid-filled metal cup. A wire attached to the cup, in turn, led to a distant receiver. As the wire moved up and down it changed the resistance within the liquid. This now varying current was then sent to the receiver, causing its membrane to vibrate and thereby produce sound. This telephone wasn't quite practical; it got speech across, but badly. This transmitter was quickly dropped in favor of voice-powered or induced models. This transmitted speech on the weak electro-magnetic force that the transmitter and receiver's permanent magnets produced.

 

Finally, on March 10, 1876, one week after his patent was allowed, Bell succeeded in transmitting speech. He was not yet 30. Bell soon improved it by using an electromagnetic transmitter, a metal diaphragm, and a permanent magnet. The telephone had been invented.

       

 

 

 

 

 

 

 

 

      

 

 

 

 

 

 

 

 

  

The human voice on wires

 Simply using two insulated iron wires overhead along the streets, a human voice could be transmitted as an electrical signal generated by a telephone apparatus. If all such wires are terminated on a board, the board operator[also called telephone operator] could manually interconnect these lines as required by a service user at any time. This constitutes the simple theory of a telephone exchange. If the power supply needed to run the system is supplied from the central office itself, it was called central battery exchange. Such a service evolved in the USA long back after 1876 in Bell's lab.

This networked system made things easy to communicate immediately in a local area between business offices and homes as needed. The distance of telephone lines could be increased to talk with nearby villages by erecting lines of thick weld-copper conducting materials to reduce the electric resistance. 

For a local area, about five kilometers radius was standardized; beyond that distance, the voice would be very feeble to hear. A fifty volts DC battery supply was used to run the system. One such system was installed in Calcutta during British rule in India with less than 20 lines to start with. The system was gradually expanded to other presidencies like Bombay and Madras.

Over the time, some new innovations were made and the facilities were expanded to many princely states of India. Many such CBNM and CBM systems flourished all over India before Independence.

To interconnect the switching centers, trunk lines were constructed.

At the time of Indian independence, when all princely states were integrated into a single Nation as India, a department was created, called Post and Telegraph.

In 1950 the number of telephone exchanges absorbed from princely states was 196. The installed capacity of these 196 exchanges was 13,362 lines with 11,296 working connections.

After the next two decades, when electronic diodes and transistors were made available, for the first time, the voice modulators and demodulators were manufactured and used successfully to carry more than one telephone speech over the same pair of wires, between the neighboring towns and cities. These were called speech channels.

A standard three-channel system was evolved to make it possible to run four-voice signals together on a single pair of wires [called NCJ lines]. Later, the channel capacity was increased to eight channels on C-8 trunk lines. During the 1970s, One such system was working between Pune and Hyderabad which was constructed along national highway number nine in India. Repeater stations were installed in order to increase the power loss due to transmission lines. These stations were also used to drop or inject a channel at the local exchange office. This served to branch the transmission system as needed.

The business community and the government offices were the first users of this system. Indian railways used telecom services to control the movement of trains on railroads.

Gradually almost all the district places and important towns got telephone services in India.

 

Automatic local exchanges were developed using electromagnetic relay logic systems. One 200 lines switch needed one large room to house all accessories like the battery and power plant. It would take six months to install and commission one such system. The two motion selectors were used to connect the desired number as per dialed information. 50-lines switches were used for smaller towns. The 1980s saw this development in India. After 1980, the efficiency of the telephone service gradually increased because of PVC insulated u/g cables. The switching capacity expansions started regularly to increase the services to rural areas too. Gradually, the villagers started using the telephone facility. The Government thought that there should be at least one telephone in each village for communication. Many public call offices were opened. The DOT was separated from Postal services.

The 1990s saw the line of sight communication technology to carry bulk channels using microwave transmission systems. These systems inter-connected many metros together, in the length and breadth of India. A large number of channels capacity was used to extend STD [subscriber trunk dialing] facility to important customers. STD PCOs became a good source of revenue generation for DOT.

As a final information carrier system, OFC [Optical fiber cable] transmission systems were standardized for trunk working. Electronic exchange switches were manufactured using C-DOT technology in India. This became the tool for quick expansion of switching systems in order to provide on-demand new connections in most of the urban centers. The public demand also increased to own a telephone in most households. 

The local cable and overhead lines were a weak point in the telecom system and subjected to recurring fault due to rusting of the copper conductor in the wet atmosphere, and frequent interruption became a point of concern for telephone service users.

 

Some milestones in Indian Telephone systems:

In August 1907, the Central Battery working of telephones was first introduced in Kanpur.

1913-14 First automatic exchange was installed at Simla with a capacity of 700 lines with 400 actual connections.

1925-26, Conversion of Delhi Manual system to Auto System. 

1950-55, Step by Step strowger exchanges commissioned.

In 1953, 12 channel carrier systems introduced.

July 1959, First Coaxial route between Delhi-Agra commissioned.

December 1965, the First microwave route between Calcutta-Asansol opened.

1979, First optic fiber system, for local junction working, commissioned at Pune.

1984, C-DOT was established for indigenous development and production of digital exchanges.

1987-88, Large Scale introduction of Push Button telephone instruments.

 

By the 2000s, mobile telephony evolved, where the local cable was eliminated and microwave signaling was used to establish a connection for a phone call set-up. The mobile handset would provide the battery needed to speak. Later, smartphone handsets were made to extend internet services directly to mobile phones. e-mail and other messaging services stated. Gradually all open wire systems like trunk lines were eliminated, all over the country.