The word communication means exchange of ideas and views between two or more people. Basically communication needs a common language and a source of energy for carrying the transmission, a receiver and a media through which this energy is transferred.
In electronics, the term communication means sending, receiving and processing of information by electronic means. Initially communication started with wired telegraphy in 1840s. Some decade’s later telephony came up as an evolved communication system.
In twentieth century, during World War II (1939-45) the triode (the electronic tube) was invented and that gave rise to new development in Radio Communication. It was more refined through invention of transistor in 1950s, integrated circuits in 1965 and other semi-conducting devices in the following years. More recently the use of satellite, Fibre optics with participation of computer and data communication has given the communication a new shape even more wide spread.
A modern communication system involves, sorting, processing and storing of information before transmission. Sorting means selecting of wanted information from a lot and rejecting unwanted ones. Processing involves converting the information into electrical waveforms. Then actual transmission follows after filtering of noise. Finally we have reception, which includes processing steps such as decoding (detection), storage (computer memory) and interpretation i.e., display in the form of analog or digital etc., In this reference form of communication includes, radio telephony and telegraphy, broadcasting, point to point mobile communication, computer communications, radar, radio telemetry and radio aids navigation. Most of these described briefly in following chapters. It is most evident that the world will be paralyzed if communication is detached from it.
Establishment of Communication. It is not possible to transmit the speech or low frequency signal directly into the atmosphere because of following reasons:
(a) Attenuation is more.
(b) Power required for transmission will be very high.
(c) All radio channels will interfere with each other.
(d) Length of antenna required is very high.
Thus this speech is modulated over a high frequency signal called carrier, transmitted by a device called transmitter into air or any other medium. Modulation is the process of superimposing low frequency signal upon high frequency signal (carrier). Modulation is carried out in transmitter.
This modulated signal is directed to distant end called receiver through medium. This medium may be solid, liquid or gas.
At receiving end this signal is picked up by the antenna and detected. Detection is the process of separating intelligence from carrier. Likewise a telephone call, or a picture or other type of signal is also modulated with carrier and guided through medium. At receiving end these signals are reproduced after detection.