In early times messages were sent over the wires by alternately turning electrical currents on and off, producing a series of "dots" and "dashes" in accordance with a telegraph code. There were many drawbacks of this system like it was one to one message delivery method , and was wire dependent or we can say the media was the wires that had a network between the places where the communication was needed. Another was the data transferred in coded form, special training was needed to code and decode the data.
But with the more development in science, a significant advancement in communications was the developed as radio, or wireless communication. It proved to be revolution in communication field. Radio extended the communication range to ships in the sea and to remote areas of the world, providing for the first time instantaneous and worldwide communication.
After people learned how to encode and decode the human voice in a form that could be super imposed on electromagnetic waves and transmitted to a receiver, they used this mode as radio communication directly with human speech. So the human voice was transmitted thousands of miles, picked up by receivers and converted back into speech by loudspeakers. It was like revolution in the field of communication. Radio came to be the first complete electronic communication system. Speech now could be transferred from one part of the earth to another or from a point on earth to a point in space. This was not limited to land or land to space but also from land to sea and sea to space. Also the message delivery rate was increased to the speed of light, making international communications possible within fractions of second, and space communications within seconds. Now communicating with the soldiers or people on the far most outskirts was not a big deal.
The radiation concept of radio waves can be visualized by dropping a pebble into a pool of still water. As the pebble enters the water, a surface disturbance is created, causing the water to move up and down. From this point, the disturbance is transmitted on the surface of the pool in the form of expanding circles of waves. Here the water is not moving away from the point. The type of wave here produced is called the transverse wave. That is the wave occurring in a direction or directions perpendicular to the direction of wave propagation. Same are the characteristics of the radio waves.
Although there is no clear cut demarcation between radio waves and micro waves, electromagnetic waves ranging in frequencies between three kilohertz and one gigahertz are normally called radio waves. However the behavior of waves, rather than the frequencies is a better criterion for classification.
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