Explore the fascinating history of ELECTRONIC MEDIA from its early days to the digital age. Learn how this powerful medium has evolved over the years.
History of Electronic Media
Transmission and detection of communication signals consisting of electromagnetic waves those travel through the air in a straight line or by reflection from the ionosphere or from a communications satellite. Electromagnetic radiation includes light as well as radio waves, and the two have many properties in common. Both are propagated through space in approximately straight lines at a velocity of about 300,000,000 metres (186,000 miles) per second and have amplitudes that very cyclically with time; that is, they swing from zero amplitude to a maximum and back again. The number of times the cycle is repeated in one second is called the frequency (symbolized as I) in cycles per second, and the time taken to complete one cycle is l/f seconds, sometimes called the period.
To honour the German pioneer Heinrich Hertz, who carried out some of the early radio experiments, the cycle per second is now called a hertz so that a frequency of one cycle per second is written as one hertz (abbreviated Hz). A radio wave being propagated through space will at any given instant have an amplitude variation along its direction of travel similar to that of its time variation, much like a wave travelling on a body of water.
The distance from one wave crest to the next is known as the WAVELENGTH Wavelength and frequency are related Dividing the speed of the electromagnetic wave (c) by the wavelength (designated by the Greek letter lambda, L) gives the frequency f = c/L. Thus a wavelength of 10 metres has a frequency of 300,000,000 divided by 10, or 30,000,000 hertz (30 megahertz). The wavelength of light is much shorter than that of a radio wave At the centre of the light spectrum the wavelength is about 0.5 micron (0.0000005 metre), or a frequency of 6′ 1014 hertz or 600,000 gigahertz (one gigahertz equals 1,000,000,000 hertz).
The maximum frequency in the radio spectrum is usually taken to be about 45 gigahertz corresponding to a wavelength of about 6 7 millimetres Radio waves can be generated and used at frequencies lower than 10 kilohertz (I
‘0,000 metres). Mechanism of wave propagation, a radio wave is made up of electric and magnetic fields vibrating mutually af right .ingles to each other in space. When these two fields are operating synchronously in time, they are said to be in time phase; i e, both reach their maxima and minima together and both go through zero together.
As the distance from the source of energy increases, the area over which the electric and magnetic energy is spread is increased, so that the available energy per unit area is decreased Radio signal intensity, like light intensity, decreases as the distance from the source increases.
A TRANSMITTING ANTENNA is 3 device that projects the radio-frequency energy generated by a transmitter into space. The antenna can be designed to concentrate the radio energy into a beam like a searchlight and so increase its effectiveness in a given direction Electromagnetic radiation includes light as well as radio waves, and the two have manv properties in common. Both are propagated through space in approximately straight lines at a velocity of about 300,000.000 metres (186,000 miles) per second and have amplitudes that van cyclically with time, that is, they oscillate from zero amplitude to a maximum and back again. The number of times the cycle is repeated in one second is called the frequency (symbolized as f) in cycles per second, and the time taken to complete one cvcle is I f seconds, sometimes called the period.
History of Radio
Development of radio technology MAXWELL’S prediction Early in the 19th century, MICHAEL FARADAY, an English physicist, demonstrated that an electric current can produce a local magnetic field and that the energy in this field will return to the circuit when the current is stopped or changed JAMES CLERK MAXWELL, professor of experimental physics at Cambridge, in 1864 proved mathematically that any electrical disturbance could produce an effect at a considerable distance from the point at which it occurred and predicted that electromagnetic energy could Hertz: radio-wave experiments at the time of Maxwell’s prediction there were no known means of propagating or detecting the presence of electromagnetic waves in space.
It was not uptil about 1888 that Maxwell’s theory was tested by Heinrich Hertz, who demonstrated that Maxwell’s predictions were true at least Over short distances by installing a spark gap (two conductors separated by a short gap) at the centre of a parabolic metal mirror A wire ring connected to another spark gap was placed about five feet (15 metres) away at the focus of another parabolic collector in line with the first.
A spark jumping across the first gap caused a smaller spark to jumping across the gap in the ring five feet away Hertz showed that the waves travelled in straight lines and that they could be reflected by a metal sheet just as light waves are reflected by a mirror Development of radio technology Printed circuits With printed wiring, the layout of the circuit is planned with component size and position in mind, and connections are made by suitably shaped copper strip or foil bonded to an insulating board or substrate.
An extension of this technique was the printed component, resistors, capacitors, and low value inductors became a part of the printing process. The development of the transistor simplified the exploitation of printed circuitry by eliminating one of the bulkiest components, the vacuum tube Further development led to the manufacture of the integrated circuit in the 1960s. Compact circuits of this type can perform a multiplicity of tasks such as amplification and switching.
They are widely used in computers where space is at a premium Integrated- circuit amplifiers are likely to become more important because of their ability to amplify very high frequencies The size of a portable receiver constructed from microminiature circuits is now dictated almost* entirely by the loudspeaker and the quality of reproduction required. The smaller the loudspeaker the lower the power it can accept and the less the output of low audio frequencies.
As radio moved out of the experimental era, early radio stations began to apply technology to bring music and news to a large number of people.
The First World War had given impetus to the development of radio for military purposes, and to the training of wireless operators. With the ending of the war, crystal sets tuned in by their “cat’s whisker” became immensely popular The valve-called the magic lantern of radio-developed during 1904 to 1914, soon usurped the place of the crystal.
A ban imposed on amateur radio in Britain at the outbreak of the First World War was not lifted until 1919. but in February 1920 the Marconi company in the (J K began broadcasting from WRITTLE, though later in the year the post office withdrew permission for these broadcasts.
However, on 14 February 1922 the first regular broadcasting service in Britain was again began from WRITTLE.
The BBC, set up by royal Charter came into existence on first January, 1927 and was to hold a monopoly of broadcasting in the U.K until commercial radio was legalized the SOt’.XD broadcasting act 1972.
On May 16, 1924 the 1st radio club in India was started in MADRAS which began the first broadcasting service on July 31 1924 but it was wound up in October 1927.
Before partition in 1928, a small radio station was established in Lahore by the FA/C4. In 1933, a series of speeches were broadcast but in 1936 it was wound up On December 16, 1937 Lahore radio station was recognized in Fazal Hussain building near Simla Hill After partition Lahore radio station became the heritage of Pakistan Now there 16 radio stations in Pakistan and one in Azad Kashmir On August 15.1947. Radio Pakistan news service began from Lahore, Peshawar and Dacca separately Quaid-i-Azam’s first broadcast to the nation was made on August, 31, 1947. Radio Pakistan participated in the international high frequency broadcasting conference at Mexico.
History of Television
Early ideas for the realization of television assumed the transmission of every picture element simultaneously, each over a. separate circuit (as, for example, a system suggested by GEORGE CAREY of Boston in 1875); but in about 1880 the important principle-subsequently adopted in all forms of television—Of rapidly scanning each element in the picture in succession, line by line and frame by frame, with reliance on persistence of human vision, was proposed, notably by W.E. SAWYER in the United States and MAC RICE LEBLANC in France.
This established the possibility of using only a single w ire or channel for transmission In 1873 the photoconductive properties of the element selenium were discovered; that is, the fact that its electrical conduction varied with the amount of illumination. This appeared to provide an important clue to the secret of practical television and led in 1884 to a patent by PAUL NIPKOW in Germany of a complete television system.
The distinctive feature of Nipkow’s system was the spirally gapped rotating disk that provided, at both sending and receiving ends, a simple and effective method of image scanning. Until the advent of electronic scanning, all workable television systems depended on some form or variation (e g . mirror drums, lensed disks, etc.) of the mechanical sequential scanning method exemplified by the Nipkow disk. Nipkow disk is for an 18-line picture.
The image to be televised is focussed on a rotating disk having square apertures arranged in a spiral As the disk rotates, the outermost aperture traces out a line across the top of the image, and the light passing through the aperture varies in direct proportion to the light and shade (i.e., brightness values) of that line of the image as it is traversed by the gap When the outermost gap has passed over the image, the next inner gap traces.
The changes in the light passing through the second gap represent, in sequence, the brightness values present in the image along this second line. As the disk continues to rotate, successive lines are traced out, one beneath the other, until the whole area of the image has been explored, one line at a time The process is repeated with each rotation of the disk; the more gaps, and hence lines, the greater the detail that can be analyzed In this way the detail of the whole image is sequentially explored in an orderly manner. The light passing through the apertures enters a photoelectric cell that translates the sequence of light values into a corresponding sequence of electric values.
These are transmitted over a single circuit to the receiver, where the electrical impulses cause light to be produced by a lamp (such as a gas-discharge lamp) capable of reproducing the sequence of light values: The light from the lamp is projected onto the surface of a disk similar to that at the transmitter. This disk must rotate in precise synchronism, and, by a scanning process the reverse of that already described, the brightness values are reassembled in their proper positions and the original image is reproduced. Provided the rotation is at sufficient speed, persistence of vision enables the eye to seethe image as a whole rather than as a series of moving points.