This unit examines the following arms of the broadcast media:
At the end of this unit, you should be able to:
- discuss television as a broadcast medium
- discuss radio as broadcast medium.
3.1 Radio: The First Broadcast
Telegraph and telephone were important predecessors of radio. Samuel Morse developed the telegraph in 1844 and it was a principal means of news and information. Alexander Graham Bell demonstrated his telephone in 1876 and this invention gave birth to the concept of “broadcasting” i.e. sending of a single message as sound which can be simultaneously received by large numbers of people in different locations.
In Germany, Heinrich Rudolf Hertz successfully transmitted electromagnetic waves without any other form of conduction. Hertz’s name is adopted as the measure of all radio frequencies (i.e. MHz-Mega Hertz). In 1906, De Forest perfected the audio tube, which became the vacum tube, making possible the clear transmission of voice and music. On Xmas eve (1906), Reginald Fessenden made what is generally regarded as the first broadcast. Greater success came with the replacement of Fessenden’s primitive telephone microphone with De Forest’s audio tube, which offered for greater fidelity of sound.
A series of broadcasts followed and radio began to gain ground. In 1912, the sinking of the Titanic foregrounded the potential of wireless as a lifesaver when the rescue operation was coordinated by David Sarnoff of Marconi Wireless telegraphy. Much credit for the development of radio as a national entertainment, news and commercial medium goes to David Sarnoff. Sarnoff, as an assistant traffic manager in Marconi Company in 1918 and 1916, recognized the potential of radiotelephony long before others in the field did. He wrote:
3.1.2 The Contribution of Hertz and Marconi
Heinrich Hertz, a German physicist in1888 made the sensational discovery of radio waves, a form of electromagnetic radiation with wavelengths too long for our eyes to see, confirming Maxwell’s ideas. He devised a transmitting oscillator, which radiated radio waves, and detected them using a metal loop with a gap at one side. When the loop was placed within the transmitter’s electromagnetic field, sparks were produced across the gap. This proved that electromagnetic waves could be sent out into space, and be remotely detected. These waves were known as ‘Hertzian Waves’ and Hertz managed to detect them across the length of his laboratory.
Another milestone was made by the Italian Guglielmo Marconi who was fascinated by Hertz’s discovery, and realised that if radio waves could be transmitted and detected over long distances, wireless telegraphy could be developed. He started experimenting in 1894 and set up rough aerials on opposite sides of the family garden. He managed to receive signals over a distance of 100 metres, and by the end of 1895, had extended the distance to over a mile. He approached the Italian Ministry of Posts and Telegraphs, informing them of his experiments. The Ministry was not interested and so his cousin, Henry Jameson-Davis arranged an interview with Nyilliam Preece, who was Engineer-in-Chief to the British Post Office.
He came to England in February 1896 and gave demonstrations in London at the General Post Office Building. His transmissions were detected 1.5 miles away, and on 2nd September at Salisbury plain the range was increased to 8 miles. In 1897 he obtained a patent for wireless telegraphy, and established the Wireless Telegraph and Signal Company at Chelmsford. The world’s first radio factory was opened there in 1898. On 11th May 1897 tests were carried out to establish that contacts were possible over water. A transmitter was set up at Lavernock Point, near Penarth and the transmissions were received on the other side of the Bristol Channel at the Island of Holm, a distance of 3.5 miles. The Daily Express was the first newspaper to obtain news by wireless telegraphy in August 1898, and in December of that year communication was set up between Queen Victoria’s Royal yacht, off Cowes and Osborne House. The Queen received regular bulletins on the Prince of Wales’ health, by radio, from the yacht, where he was convalescing.
Also in December of that year, wireless communication was set up between the East Goodwin light ship and the South Foeland lighthouse. On 3rd March 1899 Marconi obtained a lot of publicity when the first life was saved by wireless telegraphy, which was used to save a ship in distress in the North Sea. By the summer cross channel communication had been established and the first ocean newspaper published bulletins sent by wireless.
About this time Marconi began to develop tuned circuits for wireless transmission, so that a wireless can be tuned to a particular frequency, to remove all other transmissions except the one of interest. He patented this on 26th April 1900, under the name of ‘Tuned Syntonic Telegraphy’.On Thursday 12th December 1901, Marconi and his associates succeeded in transmitting a signal across the Atlantic Ocean. He sailed to Newfoundland with G.S. Kemp and P.W. Paget, and received a transmission from Poldhu, Cornwall. The transmission was received at Signal Hill using a kite aerial. The British government and admiralty were greatly impressed and many people wanted to invest in the new technology. Demand grew and large numbers of ships carried the new apparatus, which saved many lives at sea. One of the most famous occasions was when the Titanic sank. Signals transmitted by its Marconi wireless summoned help and saved many lives.
Receivers at this time were mainly crystal sets, which were extremely insensitive and unselective. They were connected to a pair of headphones and required a long aerial.
3.1.3 Landmarks in Radio History
- Discovery of electromagnetic induction by Michael Faraday In 1831. Faraday used mathematical models suggested by Faraday’s law of induction to propose that electromagnetic forces extended into the empty space around the conductor.
- William Henry Ward in April 1872 received U.S. Patent 126,356 for radio development.
- Maxwell equations were developed by James Clerk Maxwell and between 1861 and 1865, James Clerk Maxwell made experiments with electromagnetic waves. In 1873, as a result of experiments, Maxwell first described the theoretical basis of the propagation of electromagnetic waves in his paper to the Royal Society, “A Dynamical Theory of the Electromagnetic Field”.
- In July 1872, Mahlon Loomis received U.S. Patent 129,971 for a “wireless telegraph”. This patent utilizes atmospheric electricity to eliminate the overhead wire used by the existing telegraph systems. It did not contain diagrams or specific methods. It is substantially similar to William Henry Ward’s patent.
- Towards the end of 1875, while experimenting with the telegraph, Thomas Edison noted a phenomenon that he termed “etheric force”, announcing it to the press on November 28. He abandoned this research when Elihu Thomson, among others, ridiculed the idea.
- Between 1893 and 1894, Roberto Landell de Moura, a Brazilian priest and scientist, conducted experiments. He did not publicize his achievement until 1900.
- In 1878, David E. Hughes was the first to transmit and receive radio waves when he noticed that his induction balance caused noise in the receiver of his homemade telephone. He demonstrated his discovery to the Royal Society in 1880 but was told it was merely induction.
- In 1884, Temistocle Calzecchi-Onesti at Fermo in Italy invented a tube filled with iron filings, called a “coherer”.
- Between 1884 and 1886, Edouard Branly of France produced an improved version of the coherer.
- In 1885, Edison took out U.S. Patent 465,971 on a system of radio communication between ships (which later he sold to Marconi).
- Between 1886 and 1888, Heinrich Rudolf Hertz validated Maxwell’s theory through experiment. He demonstrated that radio radiation had all the properties of waves (now called Hertzian waves), and discovered that the electromagnetic equations could be reformulated into a partial differential equation called the wave equation. But he saw no practical use for his discovery. For more information see Hertz’s radio work.
- Claims have been made that Murray, Kentucky farmer Nathan Stubblefield invented radio between 1885 and 1892, before either Tesla or Marconi, but his devices seemed to have worked by induction transmission rather than radio transmission.
- Nikola Tesla developed means to reliably produce radio frequencies, publicly demonstrated the principles of radio, and transmitted long distance signals. He holds the US patent for the invention of the radio, defined as “wireless transmission of data”. In 1891 Tesla began his research into radio. He later published an article, “The True Wireless”, concerning this research. Tesla was the first to apply the mechanism of electrical conduction to wireless practices.
- Oliver Lodge transmitted radio signals on August 14, 1894 (one year after Tesla and one year before Marconi) at a meeting of the British Association for the Advancement of Science at Oxford University. On 19 August 1894 Lodge demonstrated the reception of Morse code signalling via radio waves using a “coherer”. He improved Edouard Branly’s coherer radio wave detector by adding a “trembler” which dislodged clumped filings, thus restoring the device’s sensitivity. In August 1898 he got U.S. Patent 609,154 , “Electric Telegraphy”, that made wireless signals using Ruhmkorff coils or Tesla coils for the transmitter and a Branly coherer for the detector. This was key to the “syntonic” tuning concept. In 1912 Lodge sold the patent to Marconi
- In November 1894, the Bengali Indian physicist, Jagdish Chandra Bose, demonstrated publicly the use of radio waves in Calcutta, but he was not interested in patenting his work. Bose ignited gunpowder and rang a bell at a distance using electromagnetic waves, proving that communication signals can be sent without using wires. The 1895 public demonstration by Bose in Calcutta was before Marconi’s wireless signalling experiment on Salisbury Plain in England in May 1897. In 1896, the Daily Chronicle of England reported on his UHF experiments: “The inventor (J.C. Bose) has transmitted signals to a distance of nearly a mile and herein lies the first and obvious and exceedingly valuable application of this new theoretical marvel.”
- Alexander Popov was the first man to demonstrate the practical applications of radio waves. In 1894, the Russian physicist Alexander Popov built a coherer. On May 7, 1895, Popov performed a public demonstration of transmission and reception of radio waves used for communication at the Russian Physical and Chemical Society, using his coherer. Around March 1896 Popov demonstrated in public the transmission of radio waves, between different campus buildings, to the Saint Petersburg Physical Society. (This was before the public demonstration of the Marconi system around September 1896). In 1898 his signal was received 6 miles away, and in 1899 30 miles away. In 1900, Popov stated at the Congress of Russian Electrical Engineers that, “the emission and reception of signals by Marconi by means of electric oscillations was nothing new, as in America Nikola Tesla did the same experiments in 1893.”Later Popov experimented with ship-to-shore communication. Popov died in 1905 and his claim was not pressed by the Russian government until 1945.
- In February 1893, Tesla delivers “On Light and Other High Frequency Phenomena” before the Franklin Institute in Philadelphia. In 1895, Marconi receives a telegraph message without wires a short distance (below a mile), but he did not send his voice over the airwaves. In March 1895, Popov transmitted radio waves between campus buildings in Saint Petersburg, but did not apply for a patent. In 1896, Tesla detected transmissions from his New York lab of low frequency (50,000 cycle per second) undamped waves with a receiver located at West Point, “a distance of about 30 miles.”
SELF ASSESSMENT EXERCISE 1
Radio as a medium of mass communication is said to have the highest number of audience and widest reach. Do you agree? Give reason for your answer.
3.2 Television: The Most Influential Medium
The word television is a hybrid word, created from both Greek and Latin. Tele- is Greek for “far”, while -vision is from the Latin visio, meaning “vision” or “sight”. It is often abbreviated as TV or the telly.
3.2.1 History of television
The History of television technology can be divided along two lines: those developments that depended upon both mechanical and electronic principles, and those which are purely electronic. From the latter descended all modern televisions, but these would not have been possible without discoveries and insights from the mechanical systems.
The operation basis for modern television could be traced to the development of the first workable device for generating electrical signals suitable for the transmission of a scene that people should see. Today’s television system could be traced back to the discovery of the photoconductivity of the element selenium by Willoughby Smith in 1873, and the invention of a scanning disk in 1884 by a German student whose name was Paul Gottlieb Nipkow. Nipkow proposed and patented the first electromechanical television system in 1884. Nipkow’s spinning disk design is credited with being the first television image rasterizer. Constantin Perskyi had coined the word television in a paper read to the International Electricity Congress at the International World Fair in Paris on August 25, 1900. Perskyi’s paper reviewed the existing electromechanical technologies, mentioning the work of Nipkow and others. The photoconductivity of selenium and Nipkow’s scanning disk were first joined for practical use in the electronic transmission of still pictures and photographs, and by the first decade of the 20th century halftone photographs were being transmitted by facsimile over telegraph and telephone lines as a newspaper service.
Developments in amplification tube technology later came in 1907. The first demonstration of the instantaneous transmission of still duotone images was by Georges Rignoux and A. Fournier in Paris in 1909, using a rotating mirror-drum as the scanner, and a matrix of 64 selenium cells as the receiver. This was advanced by Boris Rosing and his student Vladimir Kosma Zworykin in 1911, when they created a television system that used a mechanical mirror-drum scanner to transmit, in Zworykin’s words, “very crude images” over wires to the electronic Braun tube (cathode ray tube) in the receiver. Moving images were not possible because, in the scanner, “the sensitivity was not enough and the selenium cell was very laggy”.
3.2.2 Some Landmarks in Television History
- John Logie Baird, a Scottish inventor on March 25, 1925, gave a demonstration of televised silhouette images in motion at Selfridge’s Department Store in London. Baird gave the world’s first public demonstration of a working television system to members of the Royal Institution and a newspaper reporter on January 26, 1926 at his laboratory in London.
- In 1927, Baird transmitted a signal over 438 miles of telephone line between London and Glasgow.
- In 1928 Baird Television Development Company / Cinema Television broadcast the first transatlantic television signal, between London and New York, and the first shore-to-ship transmission. He also demonstrated an electromechanical color, infrared (dubbed “Noctovision”), and stereoscopic television, using additional lenses, disks and filters.
- In 1929, Baird became involved in the first experimental electromechanical television service in Germany. In 1931 he made the first live transmission, of the Epsom Derby. In 1932 he demonstrated ultra-short wave television. Baird’s electromechanical system reached a peak of 240 lines of resolution on BBC television broadcasts in 1936, before being discontinued in favour of a 405-line all-electronic system developed by Marconi-EMI.
- On June 13, 1925 in the U.S., Charles Francis Jenkins demonstrated the transmission of the silhouette image of a toy windmill in motion from a naval radio station to his laboratory in Washington, using a lensed disk scanner with 48 lines per picture, 16 pictures per second. AT&T’s Bell Telephone Laboratories transmitted half-tone images of transparencies in May 1925.
- On April 7, 1927, Herbert E. Ives of Bell Labs showcased a dramatic demonstration of television when he field tested reflected-light television systems using small-scale (2 by 2.5 inches) and large-scale (24 by 30 inches) viewing screens over a wire link from Washington to New York City, and over-the-air broadcast from Whippany, New Jersey.
- Alan Archibald Campbell-Swinton, an engineer gave a speech in London in 1911, reported in The Times, describing in great detail how distant electric vision could be achieved by using cathode ray tubes at both the transmitting and receiving ends. The speech, which expanded on a letter he wrote to the journal Nature in 1908, was the first iteration of the electronic television method that is still used today.
- Kálmán Tihanyi, a Hungarian inventor in 1926 showcased television operating on the basis of continuous electron emission with accumulation and storage of released secondary electrons during the entire scansion cycle.
- Philo Farnsworth on September 7, 1927, presented its Image Dissector camera tube which transmitted its first image, a simple straight line, at Farnsworth’s laboratory at 202 Green Street in San Francisco.
- On 25 August 1934, Farnsworth gave the world’s first public demonstration of a complete all-electronic television system at the Franklin Institute in Philadelphia
- Vladimir Zworykin and his team in 1931 successfully created their first successful electronic camera tube, dubbed the Iconoscope.
- In 1936 in Britain, Isaac Shoenburg began the world’s first high-definition regular service mast which is still in use today. Shoenburg used Zworykin’s idea to develop Marconi-EMI’s own Emitron tube, which formed the heart of the cameras they designed for the BBC.
3.2.3 Development of Colour Television
John Logie Baird was the world’s first to demonstrate colour transmission on July 3, 1928, using scanning discs at the transmitting and receiving ends with three spirals of apertures, each spiral with filters of a different primary color; and three light sources at the receiving end, with a commutator to alternate their illumination. On August 16, 1944, Baird gave a demonstration of a fully electronic colour television display.
In the electronically scanned era, the first colour television demonstration was on February 5, 1940, when RCA privately showed to members of the FCC at the RCA plant in Camden, New Jersey, a
television receiver producing colour images by optically combining the images from two picture tubes onto a single rear-projection screen.
NBC (owned by RCA) made its first field test of colour television on February 20, 1941. CBS began daily colour field tests on June 1, 1941. These color systems were not compatible with existing black and white television sets, and as no colour television sets were available to the public at this time, viewership of the colour field tests was limited to RCA and CBS engineers and the invited press. The War Production Board halted the manufacture of television and radio equipment for civilian use from April 22, 1942 to August 20, 1945, limiting any opportunity to introduce colour television to the general public.
On January 12, 1950 , CBS gave the world’s first demonstrations of colour television to the general public, showing an hour of colour programmes daily Mondays through Saturdays over WOIC in Washington, D.C., where they could be viewed on eight 16-inch colour receivers in a public building. This was done as part of the CBS campaign for FCC approval. This generated public interest and high demand.
On October 11, 1950, the FCC formally approved the CBS system as the U.S. colour broadcasting standard, after a series of hearings beginning in September 1949. The FCC found the RCA and CTI systems fraught with technical problems, inaccurate colour reproduction, and expensive equipment. An unsuccessful lawsuit by RCA delayed the world’s first network colour broadcast until June 25, 1951, when a musical variety special titled simply Premiere was shown over a network of five east coast CBS affiliates. Viewership was again extremely limited: the programme could not be seen on black and white sets, and Variety estimated that only thirty prototype colour receivers were available in the New York area. Regular colour broadcasts began that same week with the daytime series The World Is Yours and Modern Homemakers.
Gradually, CBS colour broadcasting schedule expanded to twelve hours per week and the colour network expanded to eleven affiliates as far west as Chicago, but its commercial success was doomed by the lack of colour receivers necessary to watch the programmes, the refusal of television manufacturers to create adapter mechanisms for their existing black and white sets, and the unwillingness of advertisers to sponsor broadcasts seen by almost no one.
To overcome this commercial challenge, CBS bought a television manufacturer in April, and in September 1951, production began on the first and only CBS-Columbia colour television model. But it was too little, too late. Only 200 sets had been shipped, and only 100 sold, when
CBS pulled the plug on its colour television system on October 20, 1951, and bought back all the CBS colour sets it could to prevent lawsuits by disappointed customers.
Shortly before CBS colour even got on the air, the U.S. National Television System Committee (NTSC), worked in 1950–1953 to develop a colour system that was compatible with existing black and white sets and would pass FCC quality standards, with RCA developing the hardware elements. NTSC efforts paid off in July 1953 when it was granted approval and this led to the first publicly announced experimental TV broadcast of a programme using the NTSC “compatible colour” system, an episode of NBC titled Kukla, Fran and Ollie on August 30, 1953.
3.2.4 Some Landmarks in the Development of Colour Television
- NBC made the first coast-to-coast colour broadcast when it covered the Tournament of Roses Parade on January 1, 1954, NBC was naturally at the forefront of colour programming because its parent company RCA manufactured the most successful line of colour sets in the 1950s, and by 1959 RCA was the only remaining major manufacturer of colour sets.
- Cuba became the second country in the world to introduce colour television broadcasting, with Havana’s Channel 12 using the NTSC standard and RCA equipment. This was done in 1958, but the color transmissions ended when broadcasting stations were seized in the Cuban Revolution in 1959, and did not return until 1975, using equipment acquired from Japan’s NEC Corporation, and SECAM equipment from the Soviet Union, adapted for the NTSC standard.
- Guillermo González Camarena (1917–1965), invented Mexico first colour television transmission system. He received patents for colour television systems in 1942 (U.S. Patent 2,296,019), 1960 and 1962. It was similar to field sequential color receivers already demonstrated by John Logie Baird in England in 1939 and by CBS in the United States in August 1940. He obtained authorization to make the first publicly announced colour broadcast in Mexico, on February 8, 1963, of the program Paraíso Infantil on Mexico City’s XHGC-TV.
- Canada experienced its colour television stations not until 1966. This was an extension of the rise in the neighbouring United States.
- In Europe, the delay in colour television was partly because there were fewer commercial motivations and being that European television broadcasters were predominantly state-owned at the time. Besides, there was the problem of continuing division on technical standards. In the 1950s, with the first SECAM patent being registered in 1956, many years had passed when the first broadcasts actually started in 1967. Not satisfied with the performance of NTSC and of initial SECAM implementations, the Germns unveiled PAL (phase alternating line) in 1963, technically similar to NTSC but borrowing some ideas from SECAM. The PAL system spread through most of Western Europe and on into the territories of the old British, Portuguese, Belgian, Dutch, Austro-Hungarian, Ottoman and Chinese Empires.
- In Italy, Indesit mooted the development of the ISA but the idea was scrapped. As a result, Italy was one of the last European countries to officially adopt the PAL system in 1977, after long technical experimentation.
- France, Luxembourg, and the Soviet Union along with their overseas territories opted for SECAM. SECAM was a popular choice in countries with a lot of hilly terrain, and technologically backward countries with a very large installed base of monochrome equipment, since the greater ruggedness of the SECAM signal could cope much better with poorly maintained equipment.The only real drawback of SECAM is that, unlike PAL or NTSC, post-production of an encoded SECAM is not really possible without a severe drop in quality.
- In September 10, 1960.,Japan, NHK introduced colour television, using a variation of the NTSC system (called NTSC-J), other countries in the asia-pacific region did not adopt the NTS system until much later.Instead, they used the PAL system, such as Singapore (1973), New Zealand (1973) and Australia (1975), with India not introducing it until 1982. South Korea did not introduce colour (using NTSC) until 1980, although it was already manufacturing colour television sets for export.
- In Africa, the first colour television service was introduced on the Tanzanian island of Zanzibar, in 1973, using PAL. At the time, South Africa did not have a television service at all, owing to opposition from the apartheid regime, but in 1976, one was finally launched. Nigeria adopted PAL for colour transmissions in the mid-1970s, but countries such as Ghana and Zimbabwe continued with black and white until the late 1980s.
- Brazil became the first South American country to receive colour TV, using a specially-modified version of PAL called PAL-M, combining both NTSC and PAL, in contrast to most other countries in the Americas, which had adopted NTSC. Its first transmission was February 19, 1972.
3.2.5 Television Delivery System
Television signals were first transmitted over the air, and viewing traces were limited to the number of channel that could be picked up by rooftop antenna. Now, cable, satellite delivering systems and the web are treading the number of channels and programming options. We have:
- Cable television
- Wireless cable (multichannel multipoint distribution service, MMDS).
- Direct broadcast satellite(DBS)
- High-Definition television
- Web-delivering system.-(interacting-combination of internet and broadcasting. It makes it possible to receive both television signals and the web, both over a television set and through a computer.
SELF ASSESSMENT EXERCISE 2
Recall and summarise the coming of colour television in Nigeria.
In 1897, Guglielmo Marconi, “Father of Radio”, invented a way to transmit sound- the dots and dashes of Morse’s code- without using wires. Almost immediately, Marconi’s wireless became a useful way to communicate with ships at sea. By 1901, Marconi successfully transmitted wireless signal between Europe and North America (New Foundland). In the USA, Fessenden successfully superimposed a voice on to a continuous radio wave using a telephonic microphone, enabling the transmission of speech and music. In 1904, John A. Fleming developed a glass bulb tube- the diode tube which became the basis for radio signal amplification of voice transmissions.
Television usage in the United States skyrocketed after World War II with the lifting of the manufacturing freeze, war-related technological advances, the gradual expansion of the television networks westward, the drop in set prices caused by mass production, increased leisure time, and additional disposable income. While only 0.5% of U.S. households had a television set in 1946, 55.7% had one in 1954, and 90% by 1962. In Britain, there were 15,000 television households in 1947, 1.4 million in 1952, and 15.1 million by 1968.
For many years different countries used different technical standards. France initially adopted the German 441-line standard but later upgraded to 819 lines, which gave the highest picture definition of any analogue TV system, approximately double the resolution of the British 405-line system. However this is not without a cost, in that the cameras need to produce four times the pixel rate (thus quadrupling the bandwidth), from pixels one-quarter the size, reducing the sensitivity by an equal amount. In practice the 819-line cameras never achieved anything like the resolution that could theoretically be transmitted by the 819 line system, and for color, France reverted to the same 625 lines as the European CCIR system. Eventually, the whole of Europe switched to the 625-line PAL standard, once more following Germany’s example. Meanwhile in North America the original NTSC 525-line standard from 1941 was retained.
Samuel Morse’s telegraph in 1844, Alexander Graham Bell’s telephone in 1876 and Thomas Edison’s light bulb in 1879 were important predecessors to the development of radio. The unit traced the development of radio as well as the challenges faced. Besides, major landmarks in the development were discussed in great detail.
The major people who are contributors to the development were highlighted and discussed. More importantly, the great contributions of the much acclaimed father of radio, Guglielmo Marconi were discussed.
The progress in the development of Television was encouraging because of the people’s ever growing interest in the broadcast medium. This unit was able to describe the development of Television the world over. Bedsides, the unit emphasized the development of colour television which came to consign the black and white television sets into oblivion.
The unit equally mentioned the indelible work of the following Television inventors/pioneer: John Logie Baird, Alan Blumlein, Walter Bruch (PAL television), Alan Archibald Campbell-Swinton, Allen B. DuMont, Philo Taylor Farnsworth, Charles Francis Jenkins Boris Grabovsky, Paul Gottlieb Nipkow, Constantin Perskyi, Boris Rosing, David Sarnoff, Kálmán Tihanyi, Vladimir Zworykin
6.0 TUTOR-MARKED ASSIGNMENT
Compare the development of radio to that of television.