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195-502: In radio communication , used in radio and television broadcasting , cell phones, two-way radios , wireless networking , and satellite communication , among numerous other uses, radio waves are used to carry information across space from a transmitter to a receiver, by modulating the radio signal (impressing an information signal on the radio wave by varying some aspect of the wave) in the transmitter. In radar, used to locate and track objects like aircraft, ships, spacecraft and missiles,

390-465: A directional antenna transmits radio waves in a beam in a particular direction, or receives waves from only one direction. Radio waves travel at the speed of light in vacuum and at slightly lower velocity in air. The other types of electromagnetic waves besides radio waves, infrared , visible light , ultraviolet , X-rays and gamma rays , can also carry information and be used for communication. The wide use of radio waves for telecommunication

585-418: A microphone , a video signal representing moving images from a video camera , or a digital signal consisting of a sequence of bits representing binary data from a computer. The modulation signal is applied to a radio transmitter . In the transmitter, an electronic oscillator generates an alternating current oscillating at a radio frequency , called the carrier wave because it serves to generate

780-495: A radar screen . Doppler radar can measure a moving object's velocity, by measuring the change in frequency of the return radio waves due to the Doppler effect . Radar sets mainly use high frequencies in the microwave bands, because these frequencies create strong reflections from objects the size of vehicles and can be focused into narrow beams with compact antennas. Parabolic (dish) antennas are widely used. In most radars

975-473: A " push to talk " button on their radio which switches off the receiver and switches on the transmitter. Or the radio link may be full duplex , a bidirectional link using two radio channels so both people can talk at the same time, as in a cell phone. One way, unidirectional radio transmission is called simplex . This is radio communication between a spacecraft and an Earth-based ground station, or another spacecraft. Communication with spacecraft involves

1170-524: A "cascade amplifier", which eventually consisted of chaining together up to three Audions. At this time the American Telephone and Telegraph Company was researching ways to amplify telephone signals to provide better long-distance service, and it was recognized that de Forest's device had potential as a telephone line repeater. In mid-1912 an associate, John Stone Stone , contacted AT&T to arrange for de Forest to demonstrate his invention. It

1365-596: A Doctorate in 1899 with a dissertation on the "Reflection of Hertzian Waves from the Ends of Parallel Wires", supervised by theoretical physicist Willard Gibbs . Reflecting his pioneering work, de Forest has sometimes been credited as the "Father of Radio", an honorific which he adopted as the title of his 1950 autobiography. In the late 1800s he became convinced there was a great future in radiotelegraphic communication (then known as " wireless telegraphy "), but Italian Guglielmo Marconi , who received his first patent in 1896,

1560-597: A German, Alexander Meissner, whose application would be seized by the Office of Alien Property Custodian during World War I. The subsequent legal proceedings become divided between two groups of court cases. The first court action began in January 1920 when Armstrong, with Westinghouse, which purchased his patent, sued the De Forest Company in district court for infringement of patent 1,113,149. On May 17, 1921,

1755-626: A Service Regulation specifying that "Radiotelegrams shall show in the preamble that the service is 'Radio ' ". The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world. Lee de Forest helped popularize the new word in the United States—in early 1907, he founded the DeForest Radio Telephone Company, and his letter in the 22 June 1907 Electrical World about

1950-403: A beam of radio waves emitted by a radar transmitter reflects off the target object, and the reflected waves reveal the object's location to a receiver that is typically colocated with the transmitter. In radio navigation systems such as GPS and VOR , a mobile navigation instrument receives radio signals from multiple navigational radio beacons whose position is known, and by precisely measuring

2145-569: A blurry demonstration broadcast showed that it would not be in regular use for several months. The DuMont Television Network , which had begun experimental broadcasts before the war, launched what Newsweek called "the country's first permanent commercial television network" on 15 August 1946, connecting New York City with Washington. Not to be outdone, NBC launched what it called "the world's first regularly operating television network" on 27 June 1947, serving New York City, Philadelphia, Schenectady and Washington. Baltimore and Boston were added to

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2340-464: A breakthrough when he reconfigured the control electrode, moving it from outside the tube envelope to a position inside the tube between the filament and the plate . He called the intermediate electrode a grid , reportedly due to its similarity to the "gridiron" lines on American football playing fields. Experiments conducted with his assistant, John V. L. Hogan , convinced him that he had discovered an important new radio detector. He quickly prepared

2535-541: A consolidation of each respective network's higher-rated programs onto one schedule); MyNetworkTV , a network formed from affiliates of UPN and The WB that did not affiliate with The CW, launched at the same time. FCC regulations in the United States restricted the number of television stations that could be owned by any one network, company or individual . This led to a system where most local television stations were independently owned, but received programming from

2730-458: A delay of ten months, in July 1913 AT&T, through a third party who disguised his link to the telephone company, purchased the wire rights to seven Audion patents for $ 50,000. De Forest had hoped for a higher payment, but was again in bad financial shape and was unable to bargain for more. In 1915, AT&T used the innovation to conduct the first transcontinental telephone calls, in conjunction with

2925-645: A differentiation between them. Within the industry, a tiering is sometimes created among groups of networks based on whether their programming is simultaneously originated from a central point, and whether the network master control has the technical and administrative capability to take over the programming of their affiliates in real-time when it deems this necessary – the most common example being during national breaking news events. In North America in particular, many television networks available via cable and satellite television are branded as "channels" because they are somewhat different from traditional networks in

3120-555: A famous—and rich—inventor, and perpetually short of funds, he sought to interest companies with a series of devices and puzzles he created, and expectantly submitted essays in prize competitions, all with little success. After completing his undergraduate studies, in September 1896 de Forest began three years of postgraduate work. However, his electrical experiments had a tendency to blow fuses, causing building-wide blackouts. Even after being warned to be more careful, he managed to douse

3315-421: A given bandwidth than analog modulation , by using data compression algorithms, which reduce redundancy in the data to be sent, and more efficient modulation. Other reasons for the transition is that digital modulation has greater noise immunity than analog, digital signal processing chips have more power and flexibility than analog circuits, and a wide variety of types of information can be transmitted using

3510-540: A government entity that was created in 1926 to regulate the radio industry. With some exceptions, radio stations east of the Mississippi River received official call signs beginning with the letter "W"; those west of the Mississippi were assigned calls beginning with a "K". The number of programs that these early stations aired was often limited, in part due to the expense of program creation. The idea of

3705-547: A government license, such as the general radiotelephone operator license in the US, obtained by taking a test demonstrating adequate technical and legal knowledge of safe radio operation. Exceptions to the above rules allow the unlicensed operation by the public of low power short-range transmitters in consumer products such as cell phones, cordless phones , wireless devices , walkie-talkies , citizens band radios , wireless microphones , garage door openers , and baby monitors . In

3900-527: A high-powered transmitter that was used primarily to drown out the other two.) Despite this setback, de Forest remained in the New York City area, in order to raise interest in his ideas and capital to replace the small working companies that had been formed to promote his work thus far. In January 1902 he met a promoter, Abraham White, who would become de Forest's main sponsor for the next five years. White envisioned bold and expansive plans that enticed

4095-547: A joint venture between Time Warner and the Tribune Company , and the United Paramount Network ( UPN ), formed through a programming alliance between Chris-Craft Industries and Paramount Television (whose parent, Viacom , would later acquire half and later all of the network over the course of its existence). In September 2006, The CW was launched as a "merger" of The WB and UPN (in actuality,

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4290-565: A lab room on December 31, 1906, and by February was making experimental transmissions, including music produced by Thaddeus Cahill 's telharmonium , that were heard throughout the city. On July 18, 1907, de Forest made the first ship-to-shore transmissions by radiotelephone—race reports for the Annual Inter-Lakes Yachting Association (I-LYA) Regatta held on Lake Erie —which were sent from the steam yacht Thelma to his assistant, Frank E. Butler, located in

4485-521: A large amount of syndicated programming. Other networks are dedicated to specialized programming, such as religious content or programs presented in languages other than English, particularly Spanish. The largest television network in the United States, however, is the Public Broadcasting Service ( PBS ), a non-profit, publicly owned, non-commercial educational service. In comparison to the commercial television networks, there

4680-583: A large economic cost, but it can also be life-threatening (for example, in the case of interference with emergency communications or air traffic control ). To prevent interference between different users, the emission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU), which allocates bands in the radio spectrum for different uses. Radio transmitters must be licensed by governments, under

4875-536: A large number of channels, as does UKTV . Sweden had only one television network from 1956 until the early-1990s: the public broadcaster Sveriges Television (SVT). Commercial companies such as Modern Times Group , TV4 , Viasat , and SBS Discovery have established TV networks since the 1980s although they initially aired exclusively on satellite. In 1991, TV4 became Sweden's first commercial television network to air terrestrially. Most television programming in Sweden

5070-438: A larger area, often an entire state, and become full-time affiliates to one specific metropolitan network. As well as these free-to-air channels, there are others on Australia's Pay television network Foxtel . New Zealand has one public network, Television New Zealand (TVNZ), which consists of two main networks: TVNZ 1 is the network's flagship network which carries news, current affairs and sports programming as well as

5265-593: A metal conductor called an antenna . As they travel farther from the transmitting antenna, radio waves spread out so their signal strength ( intensity in watts per square meter) decreases (see Inverse-square law ), so radio transmissions can only be received within a limited range of the transmitter, the distance depending on the transmitter power, the antenna radiation pattern , receiver sensitivity, background noise level, and presence of obstructions between transmitter and receiver . An omnidirectional antenna transmits or receives radio waves in all directions, while

5460-456: A method called "broadcast syndication", and today nearly every television station in the United States obtains syndicated programs in addition to network-produced fare. Late in the 20th century, cross-country microwave radio relays were replaced by fixed-service satellites. Some terrestrial radio relays remained in service for regional connections. After the failure and shutdown of DuMont in 1956, several attempts at new networks were made between

5655-478: A microphone photographically onto film, using parallel lines of variable shades of gray, an approach known as "variable density", in contrast to "variable area" systems used by processes such as RCA Photophone . When the movie film was projected, the recorded information was converted back into sound, in synchronization with the picture. From October 1921 to September 1922, de Forest lived in Berlin , Germany, meeting

5850-416: A monopoly for all wireless communication in the United States, had also set up a powerful transmitter. None of these companies had effective tuning for their transmitters, so only one could transmit at a time without causing mutual interference. Although an attempt was made to have the three systems avoid conflicts by rotating operations over five-minute intervals, the agreement broke down, resulting in chaos as

6045-425: A more limited information-carrying capacity and so work best with audio signals (speech and music), and the sound quality can be degraded by radio noise from natural and artificial sources. The shortwave bands have a greater potential range but are more subject to interference by distant stations and varying atmospheric conditions that affect reception. In the very high frequency band, greater than 30 megahertz,

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6240-464: A national basis. Currently, licensed national or provincial networks must be carried by all cable providers (in the country or province, respectively) with a service area above a certain population threshold, as well as all satellite providers. However, they are no longer necessarily expected to achieve over-the-air coverage in all areas (APTN, for example, only has terrestrial coverage in parts of northern Canada). In addition to these licensed networks,

6435-657: A network of radiotelephone stations along the Atlantic coast and the Great Lakes, for coastal ship navigation. However, the installations proved unprofitable, and by 1911 the parent company and its subsidiaries were on the brink of bankruptcy. De Forest also used the arc-transmitter to conduct some of the earliest experimental entertainment radio broadcasts. Eugenia Farrar sang "I Love You Truly" in an unpublicized test from his laboratory in 1907, and in 1908, on de Forest's Paris honeymoon, musical selections were broadcast from

6630-541: A network system which would distribute programming to many stations simultaneously, saving each station the expense of creating all of their own programs and expandingus transmitted from station to station to listeners across the United States. Other companies, including CBS and the Mutual Broadcasting System , soon followed suit, each network signed hundreds of individual stations on as affiliates: stations which agreed to broadcast programs from one of

6825-488: A network, becoming Ostankino Channel One . The other five networks were operated by Ground Zero. This free airwave space allowed many private television networks like NTV and TV-6 to launch in the mid-1990s. The 2000s were marked by the increased state intervention in Russian television. On 14 April 2001 NTV experienced management changes following the expulsion of former oligarch and NTV founder Vladimir Gusinsky . As

7020-641: A nightly schedule featuring the Columbia recordings. These broadcasts were also used to advertise "the products of the DeForest Radio Co., mostly the radio parts, with all the zeal of our catalogue and price list", until comments by Western Electric engineers caused de Forest enough embarrassment to make him decide to eliminate the direct advertising. The station also made the first audio broadcast of election reports—in earlier elections, stations that broadcast results had used Morse code—providing news of

7215-446: A paper on an arc transmitter , which unlike the discontinuous pulses produced by spark transmitters, created steady "continuous wave" signals that could be used for amplitude modulated (AM) audio transmissions. Although Poulsen had patented his invention, de Forest claimed to have come up with a variation that allowed him to avoid infringing on Poulsen's work. Using his "sparkless" arc transmitter, de Forest first transmitted audio across

7410-433: A patent application which was filed on January 29, 1907, and received U.S. patent 879,532 on February 18, 1908. Because the grid-control Audion was the only configuration to become commercially valuable, the earlier versions were forgotten, and the term Audion later became synonymous with just the grid type. It later also became known as the triode. The grid Audion was the first device to amplify, albeit only slightly,

7605-511: A policy that retailers had to require their customers to return a worn-out tube before they could get a replacement. This style of business encouraged others to make and sell unlicensed vacuum tubes which did not impose a return policy. One of the boldest was Audio Tron Sales Company founded in 1915 by Elmer T. Cunningham of San Francisco, whose Audio Tron tubes cost less but were of equal or higher quality. The de Forest company sued Audio Tron Sales, eventually settling out of court. In April 1917,

7800-468: A primitive spark-gap transmitter . Experiments by Hertz and physicists Jagadish Chandra Bose , Oliver Lodge , Lord Rayleigh , and Augusto Righi , among others, showed that radio waves like light demonstrated reflection, refraction , diffraction , polarization , standing waves , and traveled at the same speed as light, confirming that both light and radio waves were electromagnetic waves, differing only in frequency. In 1895, Guglielmo Marconi developed

7995-419: A public audience. Analog audio is the earliest form of radio broadcast. AM broadcasting began around 1920. FM broadcasting was introduced in the late 1930s with improved fidelity . A broadcast radio receiver is called a radio . Most radios can receive both AM and FM. Television broadcasting is the transmission of moving images by radio, which consist of sequences of still images, which are displayed on

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8190-457: A radio signal is usually concentrated in narrow frequency bands called sidebands ( SB ) just above and below the carrier frequency. The width in hertz of the frequency range that the radio signal occupies, the highest frequency minus the lowest frequency, is called its bandwidth ( BW ). For any given signal-to-noise ratio , an amount of bandwidth can carry the same amount of information ( data rate in bits per second) regardless of where in

8385-401: A rate of more than $ 5.00 per subscriber to ESPN). The providers also handle the sale of advertising inserted at the local level during national programming, in which case the broadcaster and the cable/satellite provider may share revenue . Networks that maintain a home shopping or infomercial format may instead pay the station or cable/satellite provider, in a brokered carriage deal. This

8580-669: A reference to the radiotelegraph and radiotelegraphy . The use of radio as a standalone word dates back to at least 30 December 1904, when instructions issued by the British Post Office for transmitting telegrams specified that "The word 'Radio'... is sent in the Service Instructions." This practice was universally adopted, and the word "radio" introduced internationally, by the 1906 Berlin Radiotelegraphic Convention, which included

8775-484: A research job at the Federal Telegraph Company , which produced long-range radiotelegraph systems using high-powered Poulsen arcs . One of de Forest's areas of research at Federal Telegraph was improving the reception of signals, and he came up with the idea of strengthening the audio frequency output from a grid Audion by feeding it into a second tube for additional amplification. He called this

8970-502: A result, most of the prominent reporters featured on NTV left the network. Later on 22 January 2002, the second largest private television network TV-6 , where the former NTV staff took refuge, was shut down allegedly because of its editorial policy. Five months later on 1 June, TVS was launched, mostly employing NTV/TV-6 staff, only to cease operations the following year. Since then, the four largest television networks (Channel One, Russia 1, NTV and Russia 2) have been state-owned. Still,

9165-445: A screen on a television receiver (a "television" or TV) along with a synchronized audio (sound) channel. Television ( video ) signals occupy a wider bandwidth than broadcast radio ( audio ) signals. Analog television , the original television technology, required 6 MHz, so the television frequency bands are divided into 6 MHz channels, now called "RF channels". The current television standard, introduced beginning in 2006,

9360-491: A second channel, BBC 2 (with the original service being renamed BBC 1 ). A second national commercial network was launched Channel 4 , although Wales instead introduced a Welsh-language service, S4C . These were later followed by the launch of a third commercial network, Channel 5 . Since the introduction of digital television, the BBC, ITV, Channel 4 and Channel 5 each introduced a number of digital-only channels. Sky operates

9555-468: A second or even third station providing a greater variety of content. Commercial television services also became available when private companies applied for television broadcasting licenses. Often, each new network would be identified with their channel number, so that individual stations would often be numbered "One", "Two", "Three" and so forth. The first television network in the United Kingdom

9750-583: A self-restoring detector that could receive transmissions by ear, thus making it capable of receiving weaker signals and also allowing faster Morse code sending speeds. After making unsuccessful inquiries about employment with Nikola Tesla and Marconi, de Forest struck out on his own. His first job after leaving Yale was with the Western Electric Company 's telephone lab in Chicago, Illinois. While there he developed his first receiver, which

9945-508: A single company (as is the case with the BBC), each local area had a separate television channel that was independently owned and operated, although most of these channels shared a number of programmes, particularly during peak evening viewing hours. These channels formed the ITV network . When the advent of UHF broadcasting allowed a greater number of television channels to broadcast, the BBC launched

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10140-446: A small number of stations still operating as affiliates. Most television services outside North America are national networks established by a combination of publicly funded broadcasters and commercial broadcasters. Most nations established television networks in a similar way: the first television service in each country was operated by a public broadcaster , often funded by a television licensing fee, and most of them later established

10335-441: A smaller bandwidth than the old analog channels, saving scarce radio spectrum space. Therefore, each of the 6 MHz analog RF channels now carries up to 7 DTV channels – these are called "virtual channels". Digital television receivers have different behavior in the presence of poor reception or noise than analog television, called the " digital cliff " effect. Unlike analog television, in which increasingly poor reception causes

10530-470: A spark-gap transmitter, he briefly thought that the flickering of a nearby gas flame might be in response to electromagnetic pulses. With further tests he soon determined that the cause of the flame fluctuations was due to air pressure changes produced by the loud sound of the spark. Still, he was intrigued by the idea that, properly configured, it might be possible to use a flame or something similar to detect radio signals. After determining that an open flame

10725-406: A telephone improvement device. Its high capacity (transmitting 240 telephone calls simultaneously) also made it ideal for long-distance television transmission, where it could handle a frequency band of 1 MHz. German television first demonstrated such an application in 1936 by relaying televised telephone calls from Berlin to Leipzig , 180 km (110 mi) away, by cable. AT&T laid

10920-412: A television (video) signal has a greater data rate than an audio signal . The radio spectrum , the total range of radio frequencies that can be used for communication in a given area, is a limited resource. Each radio transmission occupies a portion of the total bandwidth available. Radio bandwidth is regarded as an economic good which has a monetary cost and is in increasing demand. In some parts of

11115-537: A third party company (for example, the TV2 programme Shortland Street is produced by South Pacific Pictures ). The networks produce their own news and current affairs programs, with most of the content filmed in Auckland. Lee de Forest Lee de Forest (August 26, 1873 – June 30, 1961) was an American inventor , electrical engineer and an early pioneer in electronics of fundamental importance. He invented

11310-652: A transmitter to control the actions of a device at a remote location. Remote control systems may also include telemetry channels in the other direction, used to transmit real-time information on the state of the device back to the control station. Uncrewed spacecraft are an example of remote-controlled machines, controlled by commands transmitted by satellite ground stations . Most handheld remote controls used to control consumer electronics products like televisions or DVD players actually operate by infrared light rather than radio waves, so are not examples of radio remote control. A security concern with remote control systems

11505-562: A tumultuous career – he boasted that he made, then lost, four fortunes. He was also involved in several major patent lawsuits, spent a substantial part of his income on legal bills, and was even tried (and acquitted) for mail fraud . Despite this, he was recognised for his pioneering work with the 1922 IEEE Medal of Honor , the 1923 Franklin Institute Elliott Cresson Medal and the 1946 American Institute of Electrical Engineers Edison Medal . Lee de Forest

11700-531: A unionwide network. Until 1989, there were six television networks, all owned by the USSR Gosteleradio. This changed during Mikhail Gorbachev 's Perestroika program, when the first independent television network, 2×2 , was launched. Following the breakup of the Soviet Union, USSR Gosteleradio ceased to exist as well as its six networks. Only Channel One had a smooth transition and survived as

11895-434: A variety of license classes depending on use, and are restricted to certain frequencies and power levels. In some classes, such as radio and television broadcasting stations, the transmitter is given a unique identifier consisting of a string of letters and numbers called a call sign , which must be used in all transmissions. In order to adjust, maintain, or internally repair radiotelephone transmitters, individuals must hold

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12090-488: Is TV3 , which competes directly with both TVNZ broadcast networks. MediaWorks also operates a second network, FOUR , which airs mostly imported programmes with children's shows airing in the daytime and shows targeted at teenagers and adult between 15 and 39 years of age during prime time. MediaWorks also operates a timeshift network, TV3 + 1, and a 24-hour music network, C4 . All television networks in New Zealand air

12285-410: Is amplified in the transmitter and applied to a transmitting antenna which radiates the energy as radio waves. The radio waves carry the information to the receiver location. At the receiver, the radio wave induces a tiny oscillating voltage in the receiving antenna which is a weaker replica of the current in the transmitting antenna. This voltage is applied to the radio receiver , which amplifies

12480-701: Is spoofing , in which an unauthorized person transmits an imitation of the control signal to take control of the device. Examples of radio remote control: Radio jamming is the deliberate radiation of radio signals designed to interfere with the reception of other radio signals. Jamming devices are called "signal suppressors" or "interference generators" or just jammers. During wartime, militaries use jamming to interfere with enemies' tactical radio communication. Since radio waves can pass beyond national borders, some totalitarian countries which practice censorship use jamming to prevent their citizens from listening to broadcasts from radio stations in other countries. Jamming

12675-445: Is a telecommunications network for the distribution of television content , where a central operation provides programming to many television stations , pay television providers or, in the United States, multichannel video programming distributors . Until the mid-1980s, broadcast programming on television in most countries of the world was dominated by a small number of terrestrial networks . Many early television networks such as

12870-445: Is a digital format called high-definition television (HDTV), which transmits pictures at higher resolution, typically 1080 pixels high by 1920 pixels wide, at a rate of 25 or 30 frames per second. Digital television (DTV) transmission systems, which replaced older analog television in a transition beginning in 2006, use image compression and high-efficiency digital modulation such as OFDM and 8VSB to transmit HDTV video within

13065-433: Is an audio transceiver , a receiver and transmitter in the same device, used for bidirectional person-to-person voice communication with other users with similar radios. An older term for this mode of communication is radiotelephony . The radio link may be half-duplex , as in a walkie-talkie , using a single radio channel in which only one radio can transmit at a time, so different users take turns talking, pressing

13260-409: Is called "tuning". The oscillating radio signal from the desired station causes the tuned circuit to resonate , oscillate in sympathy, and it passes the signal on to the rest of the receiver. Radio signals at other frequencies are blocked by the tuned circuit and not passed on. A modulated radio wave, carrying an information signal, occupies a range of frequencies . The information ( modulation ) in

13455-424: Is called an uplink , while a link that transmits data from the spacecraft to the ground is called a downlink. Radar is a radiolocation method used to locate and track aircraft, spacecraft, missiles, ships, vehicles, and also to map weather patterns and terrain. A radar set consists of a transmitter and receiver. The transmitter emits a narrow beam of radio waves which is swept around the surrounding space. When

13650-642: Is capable of being developed into a really efficient detector, but in its present forms is quite unreliable and entirely too complex to be properly handled by the usual wireless operator." In May 1910, the Radio Telephone Company and its subsidiaries were reorganized as the North American Wireless Corporation, but financial difficulties meant that the company's activities had nearly come to a halt. De Forest moved to San Francisco, California, and in early 1911 took

13845-523: Is centralised except for local news updates that air on SVT2 and TV4. Until 1989, Netherlands Public Broadcasting was the only television network in the Netherlands, with three stations, Nederland 1 , Nederland 2 and Nederland 3 . Rather than having a single production arm, there are a number of public broadcasting organizations that create programming for each of the three stations, each working relatively independently. Commercial broadcasting in

14040-418: Is especially common with low-power television stations, and in recent years, even more so for stations that used this revenue stream to finance their conversion to digital broadcasts, which in turn provides them with several additional channels to transmit different programming sources. Television broadcasting in the United States was heavily influenced by radio. Early individual experimental radio stations in

14235-407: Is explained by author Tim P. Vos in his abstract A Cultural Explanation of Early Broadcast , where he determines targeted group/non-targeted group representations as well as the cultural specificity employed in the television network entity. Vos notes that policymakers did not expressly intend to create a broadcast order dominated by commercial networks. In fact, legislative attempts were made to limit

14430-564: Is in radio clocks and watches, which include an automated receiver that periodically (usually weekly) receives and decodes the time signal and resets the watch's internal quartz clock to the correct time, thus allowing a small watch or desk clock to have the same accuracy as an atomic clock. Government time stations are declining in number because GPS satellites and the Internet Network Time Protocol (NTP) provide equally accurate time standards. A two-way radio

14625-414: Is mainly due to their desirable propagation properties stemming from their longer wavelength. In radio communication systems, information is carried across space using radio waves. At the sending end, the information to be sent is converted by some type of transducer to a time-varying electrical signal called the modulation signal. The modulation signal may be an audio signal representing sound from

14820-548: Is no central unified arm of broadcast programming, meaning that each PBS member station has a significant amount of freedom to schedule television shows as they consent to. Some public television outlets, such as PBS, carry separate digital subchannel networks through their member stations (for example, Georgia Public Broadcasting ; in fact, some programs airing on PBS were branded on other channels as coming from GPB Kids and PBS World ). This works as each network sends its signal to many local affiliated television stations across

15015-544: Is the British Broadcasting Corporation ( BBC ), which is perhaps most-well known for its news agency BBC News . Owned by the Crown , the BBC funds itself in two ways. UK services branded under BBC are funded by the television license paid by British residents, as a result no advertising appears on these services. The advertising-funded arm ( BBC Studios ) employs 23,000 people worldwide including

15210-522: Is the one-way transmission of information from a transmitter to receivers belonging to a public audience. Since the radio waves become weaker with distance, a broadcasting station can only be received within a limited distance of its transmitter. Systems that broadcast from satellites can generally be received over an entire country or continent. Older terrestrial radio and television are paid for by commercial advertising or governments. In subscription systems like satellite television and satellite radio

15405-524: Is usually accomplished by a powerful transmitter which generates noise on the same frequency as the target transmitter. US Federal law prohibits the nonmilitary operation or sale of any type of jamming devices, including ones that interfere with GPS, cellular, Wi-Fi and police radars. ELF 3 Hz/100 Mm 30 Hz/10 Mm SLF 30 Hz/10 Mm 300 Hz/1 Mm ULF 300 Hz/1 Mm 3 kHz/100 km Television broadcasting A television broadcaster or television network

15600-598: The Western Electrician in Chicago. With radio research his main priority, de Forest next took a night teaching position at the Lewis Institute , which freed him to conduct experiments at the Armour Institute . By 1900, using a spark-coil transmitter and his responder receiver, de Forest expanded his transmitting range to about seven kilometers (four miles). Professor Clarence Freeman of

15795-667: The Associated Press , which he had successfully done for the 1899 contest. De Forest contracted to do the same for the smaller Publishers' Press Association. The race effort turned out to be an almost total failure. The Freeman transmitter broke down—in a fit of rage, de Forest threw it overboard—and had to be replaced by an ordinary spark coil. Even worse, the American Wireless Telephone and Telegraph Company , which claimed its ownership of Amos Dolbear 's 1886 patent for wireless communication meant it held

15990-688: The BBC , CBC , PBS , PTV , NBC or ABC in the US and in Australia evolved from earlier radio networks. In countries where most networks broadcast identical, centrally originated content to all of their stations, and where most individual television transmitters therefore operate only as large " repeater stations ", the terms "television network", " television channel " (a numeric identifier or radio frequency ) and "television station" have become mostly interchangeable in everyday language, with professionals in television-related occupations continuing to make

16185-1059: The Big Three television networks , the American Broadcasting Company (ABC), CBS (formerly the Columbia Broadcasting System) and the National Broadcasting Company ( NBC ); however, the Fox Broadcasting Company (Fox), which launched in October 1986, has gained prominence and is now considered part of the "Big Four". The Big Three provide a significant number of programs to each of their affiliates, including newscasts , prime time, daytime and sports programming, but still reserve periods during each day where their affiliate can air local programming , such as local news or syndicated programs . Since

16380-553: The Nine Network ; while their equivalents on VHF channels 7 and 10 respectively formed the Seven Network and Network 10 . Until 1989, areas outside these main cities had access to only a single commercial station, and these rural stations often formed small networks such as Prime Television . Beginning in 1989, however, television markets in rural areas began to aggregate, allowing these rural networks to broadcast over

16575-532: The Parker Building in New York City. The Radio Telephone Company was incorporated in order to promote his inventions, with James Dunlop Smith, a former American DeForest salesman, as president, and de Forest the vice president (De Forest preferred the term radio , which up to now had been primarily used in Europe, over wireless ). At the 1904 Louisiana Purchase Exposition, Valdemar Poulsen had presented

16770-504: The ionosphere without refraction , and at microwave frequencies the high-gain antennas needed to focus the radio energy into a narrow beam pointed at the receiver are small and take up a minimum of space in a satellite. Portions of the UHF , L , C , S , k u and k a band are allocated for space communication. A radio link that transmits data from the Earth's surface to a spacecraft

16965-450: The radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten (10) metres, with corresponding frequency of 3 times a power of ten, and each covering a decade of frequency or wavelength. Each of these bands has a traditional name: It can be seen that the bandwidth , the range of frequencies, contained in each band is not equal but increases exponentially as the frequency increases; each band contains ten times

17160-437: The regenerative circuit , and on October 6, 1914 U.S. patent 1,113,149 was issued for his discovery. U.S. patent law included a provision for challenging grants if another inventor could prove prior discovery. With an eye to increasing the value of the patent portfolio that would be sold to Western Electric in 1917, beginning in 1915 de Forest filed a series of patent applications that largely copied Armstrong's claims, in

17355-433: The "feedback circuit" and, by de Forest, as the "ultra-audion"). Beginning in 1913 Armstrong prepared papers and gave demonstrations that comprehensively documented how to employ three-element vacuum tubes in circuits that amplified signals to stronger levels than previously thought possible, and that could also generate high-power oscillations usable for radio transmission. In late 1913 Armstrong applied for patents covering

17550-461: The "goo anti-coherer") proved to be too crude to be commercialized, and de Forest struggled to develop a non-infringing device for receiving radio signals. In 1903, Reginald Fessenden demonstrated an electrolytic detector, and de Forest developed a variation, which he called the "spade detector", claiming it did not infringe on Fessenden's patents. Fessenden, and the U.S. courts, did not agree, and court injunctions enjoined American De Forest from using

17745-510: The "prime-time" programs that the network offered. Local stations occasionally break from regularly scheduled network programming however, especially when a breaking news or severe weather situation occurs in the viewing area. Moreover, when stations return to network programming from commercial breaks , station identifications are displayed in the first few seconds before switching to the network's logo. A number of different definitions of "network" are used by government agencies, industry, and

17940-531: The 1920s with the introduction of broadcasting. Electromagnetic waves were predicted by James Clerk Maxwell in his 1873 theory of electromagnetism , now called Maxwell's equations , who proposed that a coupled oscillating electric field and magnetic field could travel through space as a wave, and proposed that light consisted of electromagnetic waves of short wavelength . On 11 November 1886, German physicist Heinrich Hertz , attempting to confirm Maxwell's theory, first observed radio waves he generated using

18135-512: The 1950s and the 1970s, with little success. The Fox Broadcasting Company , founded by the Rupert Murdoch -owned News Corporation (now owned by Fox Corporation ), was launched on 9 October 1986 after the company purchased the television assets of Metromedia ; it would eventually ascend to the status of the fourth major network by 1994. Two other networks launched within a week of one another in January 1995: The WB Television Network,

18330-465: The 2000s saw a rise of several independent television networks such as REN (its coverage increased vastly allowing it to become a federal network), Petersburg – Channel Five (overall the same), the relaunched 2×2 . The Russian television market is mainly shared today by five major companies: Channel One, Russia 1, NTV, TNT and CTC. The major commercial television network in Brazil is Rede Globo , which

18525-613: The American Missionary Association's Talladega College in Talladega, Alabama , a school "open to all of either sex, without regard to sect, race, or color", and which educated primarily African-Americans. Many of the local white citizens resented the school and its mission, and Lee spent most of his youth in Talladega isolated from the white community, with several close friends among the black children of

18720-537: The Armour Institute became interested in de Forest's work and developed a new type of spark transmitter. De Forest soon felt that Smythe and Freeman were holding him back, so in the fall of 1901 he made the bold decision to go to New York to compete directly with Marconi in transmitting race results for the International Yacht races. Marconi had already made arrangements to provide reports for

18915-578: The CRTC: government-owned CBC Television (English) and Ici Radio-Canada Télé (French), French-language private network TVA , and APTN , a network focused on Indigenous peoples in Canada . A third French-language service, Noovo (formerly V), is licensed as a provincial network within Quebec , but is not licensed or locally distributed (outside of carriage on the digital tiers of pay television providers) on

19110-466: The District of Columbia district court. On May 8, 1924, that court concluded that the evidence, beginning with the 1912 notebook entry, was sufficient to establish de Forest's priority. Now on the defensive, Armstrong's side tried to overturn the decision, but these efforts, which twice went before the U.S. Supreme Court, in 1928 and 1934, were unsuccessful. This judicial ruling meant that Lee de Forest

19305-472: The Earth's atmosphere has less of an effect on the range of signals, and line-of-sight propagation becomes the principal mode. These higher frequencies permit the great bandwidth required for television broadcasting. Since natural and artificial noise sources are less present at these frequencies, high-quality audio transmission is possible, using frequency modulation . Radio broadcasting means transmission of audio (sound) to radio receivers belonging to

19500-543: The Eiffel Tower as a part of demonstrations of the arc-transmitter. In early 1909, in what may have been the first public speech by radio, de Forest's mother-in-law, Harriot Stanton Blatch , made a broadcast supporting women's suffrage. More ambitious demonstrations followed. A series of tests in conjunction with the Metropolitan Opera House in New York City were conducted to determine whether it

19695-478: The Fleming valve was merely a rectifier that converted alternating current to direct current. (For this reason, de Forest objected to his Audion being referred to as "a valve".) The U.S. courts were not convinced, and ruled that the grid Audion did in fact infringe on the Fleming valve patent, now held by Marconi . In contrast, Marconi admitted that the addition of the third electrode was a patentable improvement, and

19890-499: The Fox's Dock Pavilion on South Bass Island . De Forest also interested the U.S. Navy in his radiotelephone, which placed a rush order to have 26 arc sets installed for its Great White Fleet around-the-world voyage that began in late 1907. However, at the conclusion of the circumnavigation the sets were declared to be too unreliable to meet the Navy's needs and removed. The company set up

20085-549: The NBC television network in late 1947. DuMont and NBC would be joined by CBS and ABC in 1948. In the 1940s, the term "chain broadcasting" was used when discussing network broadcasts, as the television stations were linked together in long chains along the East Coast . But as the television networks expanded westward, the interconnected television stations formed major networks of connected affiliate stations. In January 1949, with

20280-492: The Netherlands is currently operated by two networks, RTL Nederland and SBS Broadcasting , which together broadcast seven commercial stations. The first television network in the Soviet Union launched on 7 July 1938 when Petersburg – Channel 5 of Leningrad Television became a unionwide network. The second television network in the Soviet Union launched on 22 March 1951 when Channel One of USSR Central Television became

20475-464: The November 1916 Wilson-Hughes presidential election . The New York American installed a private wire and bulletins were sent out every hour. About 2,000 listeners heard The Star-Spangled Banner and other anthems, songs, and hymns. With the entry of the United States into World War I on April 6, 1917, all civilian radio stations were ordered to shut down, so 2XG was silenced for the duration of

20670-587: The Panama-Pacific International Exposition at San Francisco. Radio Telephone Company officials had engaged in some of the same stock selling excesses that had taken place at American DeForest, and as part of the U.S. government's crackdown on stock fraud, in March 1912 de Forest, plus four other company officials, were arrested and charged with "use of the mails to defraud". Their trials took place in late 1913, and while three of

20865-474: The Tri-Ergon developers (German inventors Josef Engl (1893–1942), Hans Vogt (1890–1979), and Joseph Massolle (1889–1957)) and investigating other European sound film systems. In April 1922 he announced that he would soon have a workable sound-on-film system. On March 12, 1923, he demonstrated Phonofilm to the press; this was followed on April 12, 1923, by a private demonstration to electrical engineers at

21060-528: The U.S. Navy, located in Panama, Pensacola and Key West, Florida, Guantanamo, Cuba, and Puerto Rico. It also installed shore stations along the Atlantic Coast and Great Lakes, and equipped shipboard stations. But the main focus was selling stock at ever more inflated prices, spurred by the construction of promotional inland stations. Most of these inland stations had no practical use and were abandoned once

21255-595: The US, these fall under Part 15 of the Federal Communications Commission (FCC) regulations. Many of these devices use the ISM bands , a series of frequency bands throughout the radio spectrum reserved for unlicensed use. Although they can be operated without a license, like all radio equipment these devices generally must be type-approved before the sale. Below are some of the most important uses of radio, organized by function. Broadcasting

21450-611: The United States began limited operations in the 1910s. In November 1920, Westinghouse signed on "the world's first commercially licensed radio station", KDKA in Pittsburgh , Pennsylvania. Other companies built early radio stations in Detroit, Boston , New York City and other areas. Radio stations received permission to transmit through broadcast licenses obtained through the Federal Radio Commission (FRC),

21645-639: The action of the oscillating and non-oscillating audion", but the organization's board refused to let him, stating that it "strongly affirms the original award". The practical effect of de Forest's victory was that his company was free to sell products that used regeneration, for during the controversy, which became more a personal feud than a business dispute, Armstrong tried to block the company from even being licensed to sell equipment under his patent. De Forest regularly responded to articles which he thought exaggerated Armstrong's contributions with animosity that continued even after Armstrong's 1954 suicide. Following

21840-405: The air simultaneously without interfering with each other because each transmitter's radio waves oscillate at a different rate, in other words, each transmitter has a different frequency , measured in hertz (Hz), kilohertz (kHz), megahertz (MHz) or gigahertz (GHz). The receiving antenna typically picks up the radio signals of many transmitters. The receiver uses tuned circuits to select

22035-535: The arrival time of the radio waves the receiver can calculate its position on Earth. In wireless radio remote control devices like drones , garage door openers , and keyless entry systems , radio signals transmitted from a controller device control the actions of a remote device. The existence of radio waves was first proven by German physicist Heinrich Hertz on 11 November 1886. In the mid-1890s, building on techniques physicists were using to study electromagnetic waves, Italian physicist Guglielmo Marconi developed

22230-560: The bandwidth of the preceding band. The term "tremendously low frequency" (TLF) has been used for wavelengths from 1–3 Hz (300,000–100,000 km), though the term has not been defined by the ITU. The airwaves are a resource shared by many users. Two radio transmitters in the same area that attempt to transmit on the same frequency will interfere with each other, causing garbled reception, so neither transmission may be received clearly. Interference with radio transmissions can not only have

22425-414: The beam strikes a target object, radio waves are reflected back to the receiver. The direction of the beam reveals the object's location. Since radio waves travel at a constant speed close to the speed of light , by measuring the brief time delay between the outgoing pulse and the received "echo", the range to the target can be calculated. The targets are often displayed graphically on a map display called

22620-679: The brewing Russo-Japanese War , and later that year a tower, with "DEFOREST" arrayed in lights, was erected on the grounds of the Louisiana Purchase Exposition in Saint Louis, Missouri, where the company won a gold medal for its radiotelegraph demonstrations. (Marconi withdrew from the Exposition when he learned de Forest would be there). The company's most important early contract was the construction, in 1905–1906, of five high-powered radiotelegraph stations for

22815-681: The call sign KDKA . The emission of radio waves is regulated by law, coordinated by the International Telecommunication Union (ITU), which allocates frequency bands in the radio spectrum for various uses. The word radio is derived from the Latin word radius , meaning "spoke of a wheel, beam of light, ray". It was first applied to communications in 1881 when, at the suggestion of French scientist Ernest Mercadier  [ fr ] , Alexander Graham Bell adopted radiophone (meaning "radiated sound") as an alternate name for his photophone optical transmission system. Following Hertz's discovery of

23010-487: The callsign 8MK , which later became broadcasting station WWJ . In 1921, de Forest ended most of his radio research in order to concentrate on developing an optical sound-on-film process called Phonofilm . In 1919 he filed the first patent for the new system, which improved upon earlier work by Finnish inventor Eric Tigerstedt and the German partnership Tri-Ergon . Phonofilm recorded the electrical waveforms produced by

23205-444: The company's remaining commercial radio patent rights were sold to AT&T's Western Electric subsidiary for $ 250,000. During World War I, the Radio Telephone Company prospered from sales of radio equipment to the military. However, it also became known for the poor quality of its vacuum tubes, especially compared to those produced by major industrial manufacturers such as General Electric and Western Electric. Beginning in 1912, there

23400-668: The continuous waves which were needed for audio modulation , so radio was used for person-to-person commercial, diplomatic and military text messaging. Starting around 1908 industrial countries built worldwide networks of powerful transoceanic transmitters to exchange telegram traffic between continents and communicate with their colonies and naval fleets. During World War I the development of continuous wave radio transmitters, rectifying electrolytic, and crystal radio receiver detectors enabled amplitude modulation (AM) radiotelephony to be achieved by Reginald Fessenden and others, allowing audio to be transmitted. On 2 November 1920,

23595-399: The country. These local stations then carry the "network feed", which can be viewed by millions of households across the country. In such cases, the signal is sent to as many as 200+ stations or as little as just a dozen or fewer stations, depending on the size of the network. With the adoption of digital television , television networks have also been created specifically for distribution on

23790-458: The court ruled that the lack of awareness and understanding on de Forest's part, in addition to the fact that he had made no immediate advances beyond his initial observation, made implausible his attempt to prevail as inventor. However, a second series of court cases, which were the result of the patent office interference proceeding, had a different outcome. The interference board had also sided with Armstrong, and de Forest appealed its decision to

23985-440: The creation of Fox, the number of American television networks has increased, though the amount of programming they provide is often much less: for example, The CW only provides fifteen hours of primetime programming each week (along with three hours on Saturdays), while MyNetworkTV only provides ten hours of primetime programming each week, leaving their affiliates to fill time periods where network programs are not broadcast with

24180-465: The customer pays a monthly fee. In these systems, the radio signal is encrypted and can only be decrypted by the receiver, which is controlled by the company and can be deactivated if the customer does not pay. Broadcasting uses several parts of the radio spectrum, depending on the type of signals transmitted and the desired target audience. Longwave and medium wave signals can give reliable coverage of areas several hundred kilometers across, but have

24375-575: The defendants were found guilty, de Forest was acquitted. With the legal problems behind him, de Forest reorganized his company as the DeForest Radio Telephone Company, and established a laboratory at 1391 Sedgewick Avenue in the Highbridge section of the Bronx in New York City. The company's limited finances were boosted by the sale, in October 1914, of the commercial Audion patent rights for radio signalling to AT&T for $ 90,000, with de Forest retaining

24570-607: The device. Meanwhile, White set in motion a series of highly visible promotions for American DeForest: "Wireless Auto No.1" was positioned on Wall Street to "send stock quotes" using an unmuffled spark transmitter to loudly draw the attention of potential investors, in early 1904 two stations were established at Wei-hai-Wei on the Chinese mainland and aboard the Chinese steamer SS Haimun , which allowed war correspondent Captain Lionel James of The Times of London to report on

24765-503: The digital subchannels of television stations (including networks focusing on classic television series and films operated by companies like Weigel Broadcasting (owners of Movies! and Me-TV ) and Nexstar Media Group (owners of Rewind TV and Antenna TV ), along with networks focusing on music, sports and other niche programming). Cable and satellite providers pay the networks a certain rate per subscriber (the highest charge being for ESPN , in which cable and satellite providers pay

24960-495: The entertainment broadcasts he had suspended in 1910, now using the superior capabilities of vacuum-tube equipment. 2XG's debut program aired on October 26, 1916, as part of an arrangement with the Columbia Graphophone Company to promote its recordings, which included "announcing the title and 'Columbia Gramophone [ sic ] Company' with each playing". Beginning November 1, the "Highbridge Station" offered

25155-568: The existence of radio waves in 1886, the term Hertzian waves was initially used for this radiation. The first practical radio communication systems, developed by Marconi in 1894–1895, transmitted telegraph signals by radio waves, so radio communication was first called wireless telegraphy . Up until about 1910 the term wireless telegraphy also included a variety of other experimental systems for transmitting telegraph signals without wires, including electrostatic induction , electromagnetic induction and aquatic and earth conduction , so there

25350-546: The federal regulator enacted the Prime Time Access Rule , which restricted the amount of time that the networks could air programs; officials hoped that the rules would foster the development of quality local programs, but in practice, most local stations did not want to bear the burden of producing many of their own programs, and instead chose to purchase programs from independent producers. Sales of television programs to individual local stations are done through

25545-665: The first L-carrier coaxial cable between New York City and Philadelphia , with automatic signal booster stations every 10 miles (16 km), and in 1937 it experimented with transmitting televised motion pictures over the line. Bell Labs gave demonstrations of the New York–Philadelphia television link in 1940 and 1941. AT&T used the coaxial link to transmit the Republican National Convention in June 1940 from Philadelphia to New York City, where it

25740-544: The first apparatus for long-distance radio communication, sending a wireless Morse Code message to a recipient over a kilometer away in 1895, and the first transatlantic signal on 12 December 1901. The first commercial radio broadcast was transmitted on 2 November 1920, when the live returns of the Harding-Cox presidential election were broadcast by Westinghouse Electric and Manufacturing Company in Pittsburgh, under

25935-410: The first commercial radio broadcast was transmitted by Westinghouse Electric and Manufacturing Company in Pittsburgh, under the call sign KDKA featuring live coverage of the Harding-Cox presidential election . Radio waves are radiated by electric charges undergoing acceleration . They are generated artificially by time-varying electric currents , consisting of electrons flowing back and forth in

26130-481: The first practical electronic amplifier , the three-element " Audion " triode vacuum tube in 1906. This helped start the Electronic Age, and enabled the development of the electronic oscillator . These made radio broadcasting and long distance telephone lines possible, and led to the development of talking motion pictures , among countless other applications. He had over 300 patents worldwide, but also

26325-587: The first radio communication system, using a spark-gap transmitter to send Morse code over long distances. By December 1901, he had transmitted across the Atlantic Ocean. Marconi and Karl Ferdinand Braun shared the 1909 Nobel Prize in Physics "for their contributions to the development of wireless telegraphy". During radio's first two decades, called the radiotelegraphy era, the primitive radio transmitters could only transmit pulses of radio waves, not

26520-518: The four major television networks originally only broadcast a few hours of programs a week to their affiliate stations, mostly between 8:00 and 11:00 p.m. Eastern Time , when most viewers were watching television. Most of the programs broadcast by the television stations were still locally produced. As the networks increased the number of programs that they aired, however, officials at the Federal Communications Commission (FCC) grew concerned that local television might disappear altogether. Eventually,

26715-573: The general public. Under the Broadcasting Act , a network is defined as "any operation where control over all or any part of the programs or program schedules of one or more broadcasting undertakings is delegated to another undertaking or person", and must be licensed by the Canadian Radio-television and Telecommunications Commission (CRTC). Only three national over-the-air television networks are currently licensed by

26910-578: The high vacuum allowed it to operate at telephone-line voltages. With these changes the Audion evolved into a modern electron-discharge vacuum tube, using electron flows rather than ions. (Dr. Irving Langmuir at the General Electric Corporation made similar findings, and both he and Arnold attempted to patent the "high vacuum" construction, but the U.S. Supreme Court ruled in 1931 that this modification could not be patented). After

27105-458: The hopes of having the priority of the competing applications upheld by an interference hearing at the patent office. Based on a notebook entry recorded at the time, de Forest asserted that, while working on the cascade amplifier, he had stumbled on August 6, 1912, across the feedback principle, which was then used in the spring of 1913 to operate a low-powered transmitter for heterodyne reception of Federal Telegraph arc transmissions. However, there

27300-490: The idea of networking television signals (sending one station's video and audio signal to outlying stations) was born. However, the signal from an electronic television system, containing much more information than a radio signal, required a broadband transmission medium. Transmission by a nationwide series of radio relay towers would be possible but extremely expensive. Researchers at AT&T subsidiary Bell Telephone Laboratories patented coaxial cable in 1929, primarily as

27495-437: The idea was not yet technically feasible, and de Forest would not make any additional entertainment broadcasts until late 1916, when more capable vacuum-tube equipment became available. De Forest's most famous invention was the "grid Audion", which was the first successful three-element ( triode ) vacuum tube , and the first device which could amplify electrical signals. He traced its inspiration to 1900, when, experimenting with

27690-605: The inventor—however, he was also dishonest and much of the new enterprise would be built on wild exaggeration and stock fraud. To back de Forest's efforts, White incorporated the American DeForest Wireless Telegraph Company, with himself as the company's president, and de Forest the Scientific Director. The company claimed as its goal the development of "world-wide wireless". The original "responder" receiver (also known as

27885-575: The lights during an important lecture by Professor Charles S. Hastings , who responded by having de Forest expelled from Sheffield. With the outbreak of the Spanish–American War in 1898, de Forest enrolled in the Connecticut Volunteer Militia Battery as a bugler, but the war ended and he was mustered out without ever leaving the state. He then completed his studies at Yale's Sloane Physics Laboratory, earning

28080-525: The local stock sales slowed. De Forest eventually came into conflict with his company's management. His main complaint was the limited support he got for conducting research, while company officials were upset with de Forest's inability to develop a practical receiver free of patent infringement. (This problem was finally resolved with the invention of the carborundum crystal detector by another company employee, General Henry Harrison Chase Dunwoody ). On November 28, 1906, in exchange for $ 1000 (half of which

28275-402: The longest transmission distances of any radio links, up to billions of kilometers for interplanetary spacecraft . In order to receive the weak signals from distant spacecraft, satellite ground stations use large parabolic "dish" antennas up to 25 metres (82 ft) in diameter and extremely sensitive receivers. High frequencies in the microwave band are used, since microwaves pass through

28470-443: The majority of the locally produced shows broadcast by TVNZ and imported shows. TVNZ's second network, TV2 , airs mostly imported shows with some locally produced programs such as Shortland Street . TVNZ also operates a network exclusive to pay television services, TVNZ Heartland , available on providers such as Sky . TVNZ previously operated a non-commercial public service network, TVNZ 7 , which ceased operations in June 2012 and

28665-565: The manufacture of television and radio equipment for civilian use from 1 April 1942 to 1 October 1945, temporarily shutting down expansion of television networking. However, in 1944 a short film, " Patrolling the Ether ", was broadcast simultaneously over three stations as an experiment. AT&T made its first postwar addition in February 1946, with the completion of a 225-mile (362 km) cable between New York City and Washington, D.C., although

28860-471: The need for legal restrictions warned that "Radio chaos will certainly be the result until such stringent regulation is enforced." The United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram , by 1912 it began to promote the use of radio instead. The term started to become preferred by the general public in

29055-577: The network for their own programming, a method known as regional variation . This is common where small networks are members of larger networks. The majority of commercial television stations are self-owned, even though a variety of these instances are the property of an owned-and-operated television network. The commercial television stations can also be linked with a noncommercial educational broadcasting agency. Some countries have launched national television networks, so that individual television stations can act as common repeaters of nationwide programs. On

29250-530: The network through a franchising contract, except in a few major cities that had owned-and-operated stations (O&O) of a network and independent stations. In the early days of television, when there were often only one or two stations broadcasting in a given market, the stations were usually affiliated with multiple networks and were able to choose which programs would air. Eventually, as more stations were licensed, it became common for each station to be exclusively affiliated with only one network and carry all of

29445-490: The network's preferred position. As to individual stations, modern network operations centers usually use broadcast automation to handle most tasks. These systems are not only used for programming and for video server playout , but use exact atomic time from Global Positioning Systems or other sources to maintain perfect synchronization with upstream and downstream systems, so that programming appears seamless to viewers. A major international television broadcaster

29640-458: The networks. As radio prospered throughout the 1920s and 1930s, experimental television stations, which broadcast both an audio and a video signal, began sporadic broadcasts. Licenses for these experimental stations were often granted to experienced radio broadcasters, and thus advances in television technology closely followed breakthroughs in radio technology. As interest in television grew, and as early television stations began regular broadcasts,

29835-582: The next. Citytv originally began operating as a television system in 2002 when CKVU-TV in Vancouver started to carry programs originating from CITY-TV in Toronto and adopted that station's "Citytv" branding, but gradually became a network by virtue of national coverage through expansions into other markets west of Atlantic Canada between 2005 and 2013. Most local television stations in Canada are now owned and operated directly by their network, with only

30030-466: The operation of broadcaster UKTV in the UK itself. Experimental television broadcasts were started in 1929, using an electromechanical 30-line system developed by John Logie Baird . Limited regular broadcasts using this system began in 1934 and an expanded service (now known as BBC Television ) started from Alexandra Palace in November 1936. Television in the United States had long been dominated by

30225-410: The other hand, television networks also undergo the impending experience of major changes related to cultural varieties. The emergence of cable television has made available in major media markets, programs such as those aimed at American bi-cultural Latinos. Such a diverse captive audience presents an occasion for the networks and affiliates to advertise the best programming that needs to be aired. This

30420-501: The picture quality to gradually degrade, in digital television picture quality is not affected by poor reception until, at a certain point, the receiver stops working and the screen goes black. Government standard frequency and time signal services operate time radio stations which continuously broadcast extremely accurate time signals produced by atomic clocks , as a reference to synchronize other clocks. Examples are BPC , DCF77 , JJY , MSF , RTZ , TDF , WWV , and YVTO . One use

30615-502: The public and the broadcasters themselves will often refer to them as "networks" regardless. Some of these systems, such as CTV 2 and the now-defunct E! , essentially operate as mini-networks, but have reduced geographical coverage. Others, such as Omni Television or the Crossroads Television System , have similar branding and a common programming focus, but schedules may vary significantly from one station to

30810-601: The publication of Carl Dreher 's "E. H. Armstrong, the Hero as Inventor" in the August 1956 Harper's magazine, de Forest wrote the author, describing Armstrong as "exceedingly arrogant, brow beating, even brutal...", and defending the Supreme Court decision in his favor. In the summer of 1915, the company received an Experimental license for station 2XG , located at its Highbridge laboratory. In late 1916, de Forest renewed

31005-451: The radio frequency spectrum it is located, so bandwidth is a measure of information-carrying capacity . The bandwidth required by a radio transmission depends on the data rate of the information (modulation signal) being sent, and the spectral efficiency of the modulation method used; how much data it can transmit in each kilohertz of bandwidth. Different types of information signals carried by radio have different data rates. For example,

31200-408: The radio signal desired out of all the signals picked up by the antenna and reject the others. A tuned circuit (also called resonant circuit or tank circuit) acts like a resonator , similar to a tuning fork . It has a natural resonant frequency at which it oscillates. The resonant frequency of the receiver's tuned circuit is adjusted by the user to the frequency of the desired radio station; this

31395-448: The radio spectrum, the right to use a frequency band or even a single radio channel is bought and sold for millions of dollars. So there is an incentive to employ technology to minimize the bandwidth used by radio services. A slow transition from analog to digital radio transmission technologies began in the late 1990s. Part of the reason for this is that digital modulation can often transmit more information (a greater data rate) in

31590-454: The radio waves that carry the information through the air. The modulation signal is used to modulate the carrier, varying some aspect of the carrier wave, impressing the information in the modulation signal onto the carrier. Different radio systems use different modulation methods: Many other types of modulation are also used. In some types, a carrier wave is not transmitted but just one or both modulation sidebands . The modulated carrier

31785-473: The rights for sales for "amateur and experimental use". In October 1915 AT&T conducted test radio transmissions from the Navy's station in Arlington, Virginia that were heard as far away as Paris and Hawaii. The Radio Telephone Company began selling "Oscillion" power tubes to amateurs, suitable for radio transmissions. The company wanted to keep a tight hold on the tube business, and originally maintained

31980-479: The same digital modulation. Because it is a fixed resource which is in demand by an increasing number of users, the radio spectrum has become increasingly congested in recent decades, and the need to use it more effectively is driving many additional radio innovations such as trunked radio systems , spread spectrum (ultra-wideband) transmission, frequency reuse , dynamic spectrum management , frequency pooling, and cognitive radio . The ITU arbitrarily divides

32175-899: The same programming across the entire country with the only regional deviations being for local advertising; a regional news service existed in the 1980s, carrying a regional news programme from TVNZ's studios in New Zealand's four largest cities, Auckland, Wellington , Christchurch and Dunedin . In the 1960s, the service operated at the time by the New Zealand Broadcasting Corporation was four separate television stations – AKTV2 in Auckland, WNTV1 in Wellington, CHTV3 in Christchurch and DNTV2 in Dunedin – which each ran their own newscast and produced some in-house programmes, with other shows being shared between

32370-562: The sense defined above, as they are singular operations – they have no affiliates or component stations, but instead are distributed to the public via cable or direct-broadcast satellite providers. Such networks are commonly referred to by terms such as " specialty channels " in Canada or " cable networks " in the U.S. A network may or may not produce all of its own programming. If not, production companies (such as Warner Bros. Television , Universal Television , Sony Pictures Television and TriStar Television ) can distribute their content to

32565-460: The sign-on of DuMont's WDTV in Pittsburgh, the Midwest and East Coast networks were finally connected by coaxial cable (with WDTV airing the best shows from all four networks). By 1951, the four networks stretched from coast to coast, carried on the new microwave radio relay network of AT&T Long Lines . Only a few local television stations remained independent of the networks. Each of

32760-604: The simultaneous transmissions clashed with each other. De Forest ruefully noted that under these conditions the only successful "wireless" communication was done by visual semaphore "wig-wag" flags. (The 1903 International Yacht races would be a repeat of 1901—Marconi worked for the Associated Press, de Forest for the Publishers' Press Association, and the unaffiliated International Wireless Company (successor to 1901's American Wireless Telephone and Telegraph) operated

32955-624: The stations. Programmes and news footage were distributed via mail, with a programme airing in one region being mailed to another region for broadcast the following week. A network was finally established in 1969, with the same programmes being relayed to all regions simultaneously. From the 1970s to the 1990s, locally produced programmes that aired on TV One and TV2 were produced out of one of the four main studios, with TVNZ's network hub based in Wellington. Today, most locally produced programmes that are aired by both TVNZ and other networks are not actually produced in-house, instead they are often produced by

33150-469: The strength of received radio signals. However, to many observers it appeared that de Forest had done nothing more than add the grid electrode to an existing detector configuration, the Fleming valve , which also consisted of a filament and plate enclosed in an evacuated glass tube. De Forest passionately denied the similarly of the two devices, claiming his invention was a relay that amplified currents, while

33345-517: The town. De Forest prepared for college by attending Mount Hermon Boys' School in Gill, Massachusetts , for two years, beginning in 1891. In 1893, he enrolled in a three-year course of studies at Yale University 's Sheffield Scientific School in New Haven, Connecticut, on a $ 300 per year scholarship that had been established for relatives of David de Forest. Convinced that he was destined to become

33540-429: The transmitting antenna also serves as the receiving antenna; this is called a monostatic radar . A radar which uses separate transmitting and receiving antennas is called a bistatic radar . Radiolocation is a generic term covering a variety of techniques that use radio waves to find the location of objects, or for navigation. Radio remote control is the use of electronic control signals sent by radio waves from

33735-545: The two main private English-language over-the-air services, CTV and Global , are also generally considered to be "networks" by virtue of their national coverage, although they are not officially licensed as such. CTV was previously a licensed network, but relinquished this license in 2001 after acquiring most of its affiliates, making operating a network license essentially redundant (per the above definition). Smaller groups of stations with common branding are often categorized by industry watchers as television systems , although

33930-447: The two sides agreed to license each other so that both could manufacture three-electrode tubes in the United States. (De Forest's European patents had lapsed because he did not have the funds needed to renew them). Because of its limited uses and the great variability in the quality of individual units, the grid Audion would be rarely used during the first half-decade after its invention. In 1908, John V. L. Hogan reported that "The Audion

34125-471: The various networks, and it is common that a certain production firm may have programs that air on two or more rival networks. Similarly, some networks may import television programs from other countries, or use archived programming to help complement their schedules. Some stations have the capability to interrupt the network through the local insertion of television commercials, station identifications and emergency alerts . Others completely break away from

34320-408: The war. The ban on civilian stations was lifted on October 1, 1919, and 2XG soon renewed operation, with the Brunswick-Balke-Collender company now supplying the phonograph records. In early 1920, de Forest moved the station's transmitter from the Bronx to Manhattan, but did not have permission to do so, so district Radio Inspector Arthur Batcheller ordered the station off the air. De Forest's response

34515-509: The weak radio signal so it is stronger, then demodulates it, extracting the original modulation signal from the modulated carrier wave. The modulation signal is converted by a transducer back to a human-usable form: an audio signal is converted to sound waves by a loudspeaker or earphones, a video signal is converted to images by a display , while a digital signal is applied to a computer or microprocessor, which interacts with human users. The radio waves from many transmitters pass through

34710-433: Was a need for a more precise term referring exclusively to electromagnetic radiation. The French physicist Édouard Branly , who in 1890 developed the radio wave detecting coherer , called it in French a radio-conducteur . The radio- prefix was later used to form additional descriptive compound and hyphenated words, especially in Europe. For example, in early 1898 the British publication The Practical Engineer included

34905-401: Was already making impressive progress in both Europe and the United States. One drawback of Marconi's approach was his use of a coherer as a receiver, which, while providing for permanent records, was also slow (after each received Morse code dot or dash, it had to be tapped to restore operation), insensitive, and not very reliable. De Forest was determined to devise a better system, including

35100-525: Was also strong evidence that de Forest was unaware of the full significance of this discovery, as shown by his lack of follow-up and continuing misunderstanding of the physics involved. In particular, it appeared that he was unaware of the potential for further development until he became familiar with Armstrong's research. De Forest was not alone in the interference determination—the patent office identified four competing claimants for its hearings, consisting of Armstrong, de Forest, General Electric's Langmuir, and

35295-673: Was based on findings by two German scientists, Drs. A. Neugschwender and Emil Aschkinass . Their original design consisted of a mirror in which a narrow, moistened slit had been cut through the silvered back. Attaching a battery and telephone receiver, they could hear sound changes in response to radio signal impulses. De Forest, along with Ed Smythe, a co-worker who provided financial and technical help, developed variations they called "responders". A series of short-term positions followed, including three unproductive months with Professor Warren S. Johnson 's American Wireless Telegraph Company in Milwaukee, Wisconsin, and work as an assistant editor of

35490-430: Was born in 1873 in Council Bluffs, Iowa , the son of Anna Margaret ( née Robbins) and Henry Swift DeForest. He was a direct descendant of Jessé de Forest , the leader of a group of Walloon Huguenots who fled Europe in the 17th century due to religious persecution. De Forest's father was a Congregational Church minister who hoped his son would also become a pastor. In 1879 the elder de Forest became president of

35685-485: Was claimed by an attorney) and the rights to some early Audion detector patents, de Forest turned in his stock and resigned from the company that bore his name. American DeForest was then reorganized as the United Wireless Telegraph Company , and would be the dominant U.S. radio communications firm, albeit propped up by massive stock fraud, until its bankruptcy in 1912. De Forest moved quickly to re-establish himself as an independent inventor, working in his own laboratory in

35880-441: Was found that de Forest's "gassy" version of the Audion could not handle even the relatively low voltages used by telephone lines. (Owing to the way he constructed the tubes, de Forest's Audions would cease to operate with too high a vacuum.) However, careful research by Dr. Harold D. Arnold and his team at AT&T's Western Electric subsidiary determined that improving the tube's design would allow it to be more fully evacuated, and

36075-1104: Was founded in 1965. It grew to become the largest and most successful media conglomerate in the country, having a dominating presence in various forms of media including television, radio, print (newspapers and magazines) and the Internet. Other networks include Rede Bandeirantes , RecordTV , SBT , RedeTV! , TV Cultura , and TV Brasil . Australia has two national public networks, ABC Television and SBS . The ABC operates eight stations as part of its main network ABC TV , one for each state and territory, as well as three digital-only networks, ABC Kids / ABC TV Plus , ABC Me and ABC News . SBS currently operates six stations, SBS , SBS Viceland , SBS World Movies , SBS Food , NITV and SBS WorldWatch . The first commercial networks in Australia involved commercial stations that shared programming in Sydney , Melbourne , Brisbane , Adelaide and later Perth , with each network forming networks based on their allocated channel numbers: TCN-9 in Sydney, GTV-9 in Melbourne, QTQ-9 in Brisbane, NWS-9 in Adelaide and STW-9 in Perth together formed

36270-415: Was granted U.S. patent number 841387 on January 15, 1907. Subsequently, a third "control" electrode was added, originally as a surrounding metal cylinder or a wire coiled around the outside of the glass tube. None of these initial designs worked particularly well. De Forest gave a presentation of his work to date to the October 26, 1906, New York meeting of the American Institute of Electrical Engineers, which

36465-406: Was increased investigation of vacuum-tube capabilities, simultaneously by numerous inventors in multiple countries, who identified additional important uses for the device. These overlapping discoveries led to complicated legal disputes over priority, perhaps the most bitter being one in the United States between de Forest and Edwin Howard Armstrong over the discovery of regeneration (also known as

36660-607: Was now legally recognized in the United States as the inventor of regeneration. However, much of the engineering community continued to consider Armstrong to be the actual developer, with de Forest viewed as someone who skillfully used the patent system to get credit for an invention to which he had barely contributed. Following the 1934 Supreme Court decision, Armstrong attempted to return his Institute of Radio Engineers (present-day Institute of Electrical and Electronics Engineers ) Medal of Honor, which had been awarded to him in 1917 "in recognition of his work and publications dealing with

36855-431: Was operated by the British Broadcasting Corporation ( BBC ). On 2 November 1936 the BBC opened the world's first regular high-definition television service, from a 405 lines transmitter at Alexandra Palace. The BBC remained dominant until eventually on 22 September 1955, commercial broadcasting was established to create a second television network. Rather than creating a single network with local channels owned and operated by

37050-403: Was practical to broadcast opera performances live from the stage. Tosca was performed on January 12, 1910, and the next day's test included Italian tenor Enrico Caruso . On February 24, the Manhattan Opera Company's Mme. Mariette Mazarin sang "La Habanera" from Carmen and selections from the controversial "Elektra" over a transmitter located in de Forest's lab. But these tests showed that

37245-441: Was replaced by the timeshift channel TV One Plus 1. The network operated by Television New Zealand has progressed from operating as four distinct local stations within the four main centers in the 1960s, to having the majority of the content produced from TVNZ's Auckland studios at present. New Zealand also has several privately owned television networks with the largest being operated by MediaWorks . MediaWorks' flagship network

37440-420: Was reprinted in two parts in late 1907 in the Scientific American Supplement . He was insistent that a small amount of residual gas was necessary for the tubes to operate properly. However, he also admitted that "I have arrived as yet at no completely satisfactory theory as to the exact means by which the high-frequency oscillations affect so markedly the behavior of an ionized gas." In late 1906, de Forest made

37635-544: Was televised to a few hundred receivers over the NBC station W2XBS (which evolved into WNBC ) as well as seen in Schenectady, New York via W2XB (which evolved into WRGB ) via off-air relay from the New York station. NBC had earlier demonstrated an inter-city television broadcast on 1 February 1940, from its station in New York City to another in Schenectady , New York by General Electric relay antennas, and began transmitting some programs on an irregular basis to Philadelphia and Schenectady in 1941. Wartime priorities suspended

37830-595: Was to return to San Francisco in March, taking 2XG's transmitter with him. A new station, 6XC , was established as "The California Theater station", which de Forest later stated was the "first radio-telephone station devoted solely" to broadcasting to the public. Later that year a de Forest associate, Clarence "C.S." Thompson, established Radio News & Music, Inc., in order to lease de Forest radio transmitters to newspapers interested in setting up their own broadcasting stations. In August 1920, The Detroit News began operation of "The Detroit News Radiophone", initially with

38025-431: Was too susceptible to ambient air currents, de Forest investigated whether ionized gases, heated and enclosed in a partially evacuated glass tube, could be used instead. In 1905 to 1906 he developed various configurations of glass-tube devices, which he gave the general name of "Audions". The first Audions had only two electrodes , and on October 25, 1906, de Forest filed a patent for the diode vacuum tube detector , that

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