Misplaced Pages

#868131

125-500: FM802 ( エフエムはちまるに , Efu Emu Hachi Maru Ni ) (call sign JOFV-FM) is a commercial radio station based at Daiwa Minami-morimachi Building in Tenjimbashi Nichome, Kita-ku , Osaka , Japan , broadcasting on 80.2 FM from Mount Iimori to Kansai region. As a latecomer to the radio broadcasting market, it was a focal point for FM802 to differentiate from existing stations. Therefore, rather than featuring music promoted by

250-496: A light emitting diode (LED). However he just published a brief two paragraph note about it and did no further research. While investigating crystal detectors in the mid-1920s at Nizhny Novgorod, Oleg Losev independently discovered that biased carborundum and zincite junctions emitted light. Losev was the first to analyze this device, investigate the source of the light, propose a theory of how it worked, and envision practical applications. He published his experiments in 1927 in

375-427: A "radio station" as a government-licensed AM or FM station; an HD Radio (primary or multicast) station; an internet stream of an existing government-licensed station; one of the satellite radio channels from XM Satellite Radio or Sirius Satellite Radio ; or, potentially, a station that is not government licensed. AM stations were the earliest broadcasting stations to be developed. AM refers to amplitude modulation ,

500-493: A German patent on a galena cat whisker detector, but was too late to obtain patents in other countries. Jagadish Chandra Bose used crystals for radio wave detection at the University of Calcutta in his 60 GHz microwave optics experiments from 1894 to 1900. Like other scientists since Hertz, Bose was investigating the similarity between radio waves and light by duplicating classic optics experiments with radio waves. For

625-440: A Russian journal, and the 16 papers he published on LEDs between 1924 and 1930 constitute a comprehensive study of this device. Losev did extensive research into the mechanism of light emission. He measured rates of evaporation of benzine from the crystal surface and found it was not accelerated when light was emitted, concluding that the luminescence was a "cold" light not caused by thermal effects. He theorized correctly that

750-438: A bias battery, so it saw wide use in commercial and military radiotelegraphy stations. Another category was detectors which used two different crystals with their surfaces touching, forming a crystal-to-crystal contact. The "Perikon" detector, invented 1908 by Pickard was the most common. Perikon stood for " PER fect p I c K ard c ON tact". It consisted of two crystals in metal holders, mounted face to face. One crystal

875-494: A business opportunity to sell advertising or subscriptions to a broader audience. This is more efficient than broadcasting to a single country, because domestic entertainment programs and information gathered by domestic news staff can be cheaply repackaged for non-domestic audiences. Governments typically have different motivations for funding international broadcasting. One clear reason is for ideological, or propaganda reasons. Many government-owned stations portray their nation in

1000-482: A cat whisker, and produced enough audio output power to drive loudspeakers , allowing the entire family to listen comfortably together, or dance to Jazz Age music. So during the 1920s vacuum tube receivers replaced crystal radios in all except poor households. Commercial and military wireless telegraphy stations had already switched to more sensitive vacuum tube receivers. Vacuum tubes put an end to crystal detector development. The temperamental, unreliable action of

1125-429: A common educational project today thanks to its simple design. The contact between two dissimilar materials at the surface of the detector's semiconducting crystal forms a crude semiconductor diode , which acts as a rectifier , conducting electric current well in only one direction and resisting current flowing in the other direction. In a crystal radio , it was connected between the tuned circuit , which passed on

1250-456: A crystal detector in 1901. The crystal detector was developed into a practical radio component mainly by G. W. Pickard , who discovered crystal rectification in 1902 and found hundreds of crystalline substances that could be used in forming rectifying junctions. The physical principles by which they worked were not understood at the time they were used, but subsequent research into these primitive point contact semiconductor junctions in

1375-403: A day, seven days a week . Source: 34°41′52.13″N 135°30′40.78″E  /  34.6978139°N 135.5113278°E  / 34.6978139; 135.5113278 Radio broadcasting Radio broadcasting is the broadcasting of audio (sound), sometimes with related metadata , by radio waves to radio receivers belonging to a public audience . In terrestrial radio broadcasting

SECTION 10

#1732854809869

1500-410: A hugely popular pastime. The initial listening audience for the new broadcasting stations was probably largely owners of crystal radios. But lacking amplification, crystal radios had to be listened to with earphones, and could only receive nearby local stations. The amplifying vacuum tube radios which began to be mass-produced in 1921 had greater reception range, did not require the fussy adjustment of

1625-458: A kind of vacuum tube , was invented in 1904 by the English physicist John Ambrose Fleming . He developed a device that he called an "oscillation valve," because it passes current in only one direction. The heated filament, or cathode , was capable of thermionic emission of electrons that would flow to the plate (or anode ) when it was at a higher voltage. Electrons, however, could not pass in

1750-452: A metal point contact pressed against it with a thumbscrew, mounted inside a closed waveguide ending in a horn antenna to collect the microwaves. Bose passed a current from a battery through the crystal, and used a galvanometer to measure it. When microwaves struck the crystal the galvanometer registered a drop in resistance of the detector. At the time scientists thought that radio wave detectors functioned by some mechanism analogous to

1875-543: A mode of broadcasting radio waves by varying the amplitude of the carrier signal in response to the amplitude of the signal to be transmitted. The medium-wave band is used worldwide for AM broadcasting. Europe also uses the long wave band. In response to the growing popularity of FM stereo radio stations in the late 1980s and early 1990s, some North American stations began broadcasting in AM stereo , though this never gained popularity and very few receivers were ever sold. The signal

2000-585: A national boundary. In other cases, a broadcast may be considered "pirate" due to the type of content, its transmission format, or the transmitting power (wattage) of the station, even if the transmission is not technically illegal (such as a webcast or an amateur radio transmission). Pirate radio stations are sometimes referred to as bootleg radio or clandestine stations. Digital radio broadcasting has emerged, first in Europe (the UK in 1995 and Germany in 1999), and later in

2125-409: A pea-size piece of crystalline mineral in a metal holder, with its surface touched by a fine metal wire or needle (the "cat whisker"). The contact between the tip of the wire and the surface of the crystal formed a crude unstable point-contact metal–semiconductor junction , forming a Schottky barrier diode . The wire whisker is the anode , and the crystal is the cathode ; current can flow from

2250-426: A positive, non-threatening way. This could be to encourage business investment in or tourism to the nation. Another reason is to combat a negative image produced by other nations or internal dissidents, or insurgents. Radio RSA , the broadcasting arm of the apartheid South African government, is an example of this. A third reason is to promote the ideology of the broadcaster. For example, a program on Radio Moscow from

2375-403: A property called negative resistance which means the current through them decreases as the voltage increases over a part of their I–V curve . This allows a diode, normally a passive device, to function as an amplifier or oscillator . For example, when connected to a resonant circuit and biased with a DC voltage, the negative resistance of the diode can cancel the positive resistance of

2500-634: A radio broadcast depends on whether it uses an analog or digital signal . Analog radio broadcasts use one of two types of radio wave modulation : amplitude modulation for AM radio , or frequency modulation for FM radio . Newer, digital radio stations transmit in several different digital audio standards, such as DAB ( Digital Audio Broadcasting ), HD radio , or DRM ( Digital Radio Mondiale ). The earliest radio stations were radiotelegraphy systems and did not carry audio. For audio broadcasts to be possible, electronic detection and amplification devices had to be incorporated. The thermionic valve ,

2625-422: A receiver he first used a coherer consisting of a steel spring pressing against a metal surface with a current passing through it. Dissatisfied with this detector, around 1897 Bose measured the change in resistivity of dozens of metals and metal compounds exposed to microwaves. He experimented with many substances as contact detectors, focusing on galena . His detectors consisted of a small galena crystal with

SECTION 20

#1732854809869

2750-495: A retired general in the U.S. Army Signal Corps, patented the silicon carbide ( carborundum ) detector, Braun patented a galena cat whisker detector in Germany, and L. W. Austin invented a silicon–tellurium detector. Around 1907 crystal detectors replaced the coherer and electrolytic detector to become the most widely used form of radio detector. Until the triode vacuum tube began to be used during World War I, crystals were

2875-457: A significant threat to the AM broadcasting industry. It required purchase of a special receiver. The frequencies used, 42 to 50 MHz, were not those used today. The change to the current frequencies, 88 to 108 MHz, began after the end of World War II and was to some extent imposed by AM broadcasters as an attempt to cripple what was by now realized to be a potentially serious threat. FM radio on

3000-426: Is all that is necessary for a narrowband FM signal. The 200 kHz bandwidth allowed room for ±75 kHz signal deviation from the assigned frequency, plus guard bands to reduce or eliminate adjacent channel interference. The larger bandwidth allows for broadcasting a 15 kHz bandwidth audio signal plus a 38 kHz stereo "subcarrier" —a piggyback signal that rides on the main signal. Additional unused capacity

3125-428: Is called an envelope detector. The audio frequency current produced by the detector passed through the earphone causing the earphone's diaphragm to vibrate, pushing on the air to create sound waves . Crystal radios had no amplifying components to increase the loudness of the radio signal; the sound power produced by the earphone came solely from the radio waves of the radio station being received, intercepted by

3250-421: Is little affected by daily changes in the ionosphere, so broadcasters need not reduce power at night to avoid interference with other transmitters. FM refers to frequency modulation , and occurs on VHF airwaves in the frequency range of 88 to 108 MHz everywhere except Japan and Russia . Russia, like the former Soviet Union , uses 65.9 to 74 MHz frequencies in addition to the world standard. Japan uses

3375-466: Is sometimes mandatory, such as in New Zealand, which uses 700 kHz spacing (previously 800 kHz). The improved fidelity made available was far in advance of the audio equipment of the 1940s, but wide interchannel spacing was chosen to take advantage of the noise-suppressing feature of wideband FM. Bandwidth of 200 kHz is not needed to accommodate an audio signal — 20 kHz to 30 kHz

3500-453: Is subject to interference from electrical storms ( lightning ) and other electromagnetic interference (EMI). One advantage of AM radio signal is that it can be detected (turned into sound) with simple equipment. If a signal is strong enough, not even a power source is needed; building an unpowered crystal radio receiver was a common childhood project in the early decades of AM broadcasting. AM broadcasts occur on North American airwaves in

3625-493: Is the automation of radio stations. Some stations now operate without direct human intervention by using entirely pre-recorded material sequenced by computer control. Cat%27s whisker The "asymmetric conduction" of electric current across electrical contacts between a crystal and a metal was discovered in 1874 by Karl Ferdinand Braun . Crystals were first used as radio wave detectors in 1894 by Jagadish Chandra Bose in his microwave experiments. Bose first patented

3750-447: Is used by some broadcasters to transmit utility functions such as background music for public areas, GPS auxiliary signals, or financial market data. The AM radio problem of interference at night was addressed in a different way. At the time FM was set up, the available frequencies were far higher in the spectrum than those used for AM radio - by a factor of approximately 100. Using these frequencies meant that even at far higher power,

3875-500: The Alexanderson alternator . These slowly replaced the old damped wave spark transmitters. Besides having a longer transmission range, these transmitters could be modulated with an audio signal to transmit sound by amplitude modulation (AM). It was found that, unlike the coherer, the rectifying action of the crystal detector allowed it to demodulate an AM radio signal, producing audio (sound). Although other detectors used at

FM802 - Misplaced Pages Continue

4000-462: The Gunn diode and IMPATT diode are widely used as microwave oscillators in such devices as radar speed guns and garage door openers . In 1907 British Marconi engineer Henry Joseph Round noticed that when direct current was passed through a silicon carbide (carborundum) point contact junction, a spot of greenish, bluish, or yellowish light was given off at the contact point. Round had constructed

4125-554: The Marconi Research Centre 2MT at Writtle near Chelmsford, England . A famous broadcast from Marconi's New Street Works factory in Chelmsford was made by the famous soprano Dame Nellie Melba on June 15, 1920, where she sang two arias and her famous trill. She was the first artist of international renown to participate in direct radio broadcasts. The 2MT station began to broadcast regular entertainment in 1922. The BBC

4250-506: The medium wave frequency range of 525 to 1,705 kHz (known as the "standard broadcast band"). The band was expanded in the 1990s by adding nine channels from 1,605 to 1,705 kHz. Channels are spaced every 10 kHz in the Americas , and generally every 9 kHz everywhere else. AM transmissions cannot be ionospheric propagated during the day due to strong absorption in the D-layer of

4375-474: The "Perikon" detector. Since the detector would only function when the contact was made at certain spots on the crystal surface, the contact point was almost always made adjustable. Below are the major categories of crystal detectors used during the early 20th century: Patented by Karl Ferdinand Braun and Greenleaf Whittier Pickard in 1906, this was the most common type of crystal detector, mainly used with galena but also other crystals. It consisted of

4500-516: The "dots" and "dashes" of Morse code. Most coherers had to be tapped mechanically between each pulse of radio waves to return them to a nonconductive state. The coherer was a very poor detector, motivating much research to find better detectors. It worked by complicated thin film surface effects, so scientists of the time did not understand how it worked, except for a vague idea that radio wave detection depended on some mysterious property of "imperfect" electrical contacts. Researchers investigating

4625-476: The 1930s and 1940s led to the development of modern semiconductor electronics . The unamplified radio receivers that used crystal detectors are called crystal radios . The crystal radio was the first type of radio receiver that was used by the general public, and became the most widely used type of radio until the 1920s. It became obsolete with the development of vacuum tube receivers around 1920, but continued to be used until World War II and remains

4750-680: The 1960s to the 1980s was What is Communism? A second reason is to advance a nation's foreign policy interests and agenda by disseminating its views on international affairs or on the events in particular parts of the world. During the Cold War the American Radio Free Europe and Radio Liberty and Indian Radio AIR were founded to broadcast news from "behind the Iron Curtain " that was otherwise being censored and promote dissent and occasionally, to disseminate disinformation . Currently,

4875-508: The 1977 Nobel Prize in Physics . In 1949 at Bell Labs William Shockley derived the Shockley diode equation which gives the nonlinear exponential current–voltage curve of a crystal detector, observed by scientists since Braun and Bose, which is responsible for rectification . The development of microwave technology during the 1930s run up to World War II for use in military radar led to

5000-407: The 1N21 and 1N23 were being mass-produced, consisting of a slice of boron -doped silicon crystal with a tungsten wire point pressed firmly against it. The cat whisker contact did not require adjustment, and these were sealed units. A second parallel development program at Purdue University produced germanium diodes. Such point-contact diodes are still being manufactured, and may be considered

5125-582: The 76 to 90 MHz frequency band. Edwin Howard Armstrong invented wide-band FM radio in the early 1930s to overcome the problem of radio-frequency interference (RFI), which plagued AM radio reception. At the same time, greater fidelity was made possible by spacing stations further apart in the radio frequency spectrum. Instead of 10 kHz apart, as on the AM band in the US, FM channels are 200 kHz (0.2 MHz) apart. In other countries, greater spacing

FM802 - Misplaced Pages Continue

5250-480: The American Wireless Telephone and Telegraph Co. invented the rectifying contact detector, discovering rectification of radio waves in 1902 while experimenting with a coherer detector consisting of a steel needle resting across two carbon blocks. On 29 May 1902 he was operating this device, listening to a radiotelegraphy station. Coherers required an external current source to operate, so he had

5375-506: The U.S. Federal Communications Commission designates the 88–92 megahertz band in the U.S. for non-profit or educational programming, with advertising prohibited. In addition, formats change in popularity as time passes and technology improves. Early radio equipment only allowed program material to be broadcast in real time, known as live broadcasting. As technology for sound recording improved, an increasing proportion of broadcast programming used pre-recorded material. A current trend

5500-744: The US and Canada , just two services, XM Satellite Radio and Sirius Satellite Radio exist. Both XM and Sirius are owned by Sirius XM Satellite Radio , which was formed by the merger of XM and Sirius on July 29, 2008, whereas in Canada , XM Radio Canada and Sirius Canada remained separate companies until 2010. Worldspace in Africa and Asia, and MobaHO! in Japan and the ROK were two unsuccessful satellite radio operators which have gone out of business. Radio program formats differ by country, regulation, and markets. For instance,

5625-576: The US operates similar services aimed at Cuba ( Radio y Televisión Martí ) and the People's Republic of China , Vietnam , Laos and North Korea ( Radio Free Asia ). Besides ideological reasons, many stations are run by religious broadcasters and are used to provide religious education, religious music, or worship service programs. For example, Vatican Radio , established in 1931, broadcasts such programs. Another station, such as HCJB or Trans World Radio will carry brokered programming from evangelists. In

5750-681: The United States and Canada have chosen to use HD radio , an in-band on-channel system that puts digital broadcasts at frequencies adjacent to the analog broadcast. HD Radio is owned by a consortium of private companies that is called iBiquity . An international non-profit consortium Digital Radio Mondiale (DRM), has introduced the public domain DRM system, which is used by a relatively small number of broadcasters worldwide. Broadcasters in one country have several reasons to reach out to an audience in other countries. Commercial broadcasters may simply see

5875-568: The United States came from KDKA itself: the results of the Harding/Cox Presidential Election . The Montreal station that became CFCF began broadcast programming on May 20, 1920, and the Detroit station that became WWJ began program broadcasts beginning on August 20, 1920, although neither held a license at the time. In 1920, wireless broadcasts for entertainment began in the UK from

6000-626: The United States, France, the Netherlands, South Africa, and many other countries worldwide. The simplest system is named DAB Digital Radio, for Digital Audio Broadcasting , and uses the public domain EUREKA 147 (Band III) system. DAB is used mainly in the UK and South Africa. Germany and the Netherlands use the DAB and DAB+ systems, and France uses the L-Band system of DAB Digital Radio. The broadcasting regulators of

6125-412: The antenna. Therefore, it was the most common type used in commercial radiotelegraphy stations. Silicon carbide is a semiconductor with a wide band gap of 3 eV, so to make the detector more sensitive a forward bias voltage of several volts was usually applied across the junction by a battery and potentiometer . The voltage was adjusted with the potentiometer until the sound was loudest in

6250-532: The antenna. Therefore, the sensitivity of the detector was a major factor determining the sensitivity and reception range of the receiver, motivating much research into finding sensitive detectors. In addition to its main use in crystal radios, crystal detectors were also used as radio wave detectors in scientific experiments, in which the DC output current of the detector was registered by a sensitive galvanometer , and in test instruments such as wavemeters used to calibrate

6375-458: The art of crystal rectification as being close to disreputable. The crystal radio became a cheap alternative receiver used in emergencies and by people who could not afford tube radios: teenagers, the poor, and those in developing countries. Building a crystal set remained a popular educational project to introduce people to radio, used by organizations like the Boy Scouts . The galena detector,

SECTION 50

#1732854809869

6500-431: The best radio reception technology, used in sophisticated receivers in wireless telegraphy stations, as well as in homemade crystal radios. In transoceanic radiotelegraphy stations elaborate inductively coupled crystal receivers fed by mile long wire antennas were used to receive transatlantic telegram traffic. Much research went into finding better detectors and many types of crystals were tried. The goal of researchers

6625-406: The buzzer was turned off. The detector consisted of two parts mounted next to each other on a flat nonconductive base: a crystalline mineral forming the semiconductor side of the junction, and a "cat whisker", a springy piece of thin metal wire, forming the metal side of the junction Invented in 1906 by Henry H. C. Dunwoody , this consisted of a piece of silicon carbide (SiC, then known by

6750-709: The case of the Broadcasting Services of the Kingdom of Saudi Arabia , both governmental and religious programming is provided. Extensions of traditional radio-wave broadcasting for audio broadcasting in general include cable radio , local wire television networks , DTV radio , satellite radio , and Internet radio via streaming media on the Internet . The enormous entry costs of space-based satellite transmitters and restrictions on available radio spectrum licenses has restricted growth of Satellite radio broadcasts. In

6875-404: The cells I had cut out all three; so, therefore, the telephone diaphragm was being operated solely by the energy of the receiver signals. A contact detector operating without local battery seemed so contrary to all my previous experience that ... I resolved at once to thoroughly investigate the phenomenon. The generation of an audio signal without a DC bias battery made Pickard realize the device

7000-447: The circuit, creating a circuit with zero AC resistance, in which spontaneous oscillating currents arise. This property was first observed in crystal detectors around 1909 by William Henry Eccles and Pickard. They noticed that when their detectors were biased with a DC voltage to improve their sensitivity, they would sometimes break into spontaneous oscillations. However these researchers just published brief accounts and did not pursue

7125-537: The coherer and telephone earphone connected in series with a 3 cell battery to provide power to operate the earphone. Annoyed by background "frying" noise caused by the current through the carbon, he reached over to cut two of the battery cells out of the circuit to reduce the current The frying ceased, and the signals, though much weakened, became materially clearer through being freed of their background of microphonic noise. Glancing over at my circuit, I discovered to my great surprise that instead of cutting out two of

7250-718: The college teamed up with WLOE in Boston to have students broadcast programs. By 1931, a majority of U.S. households owned at least one radio receiver . In line to ITU Radio Regulations (article1.61) each broadcasting station shall be classified by the service in which it operates permanently or temporarily. Broadcasting by radio takes several forms. These include AM and FM stations. There are several subtypes, namely commercial broadcasting , non-commercial educational (NCE) public broadcasting and non-profit varieties as well as community radio , student-run campus radio stations, and hospital radio stations can be found throughout

7375-702: The company and the Carver Corporation later cut the number of models produced before discontinuing production completely. As well as on the medium wave bands, amplitude modulation (AM) is also used on the shortwave and long wave bands. Shortwave is used largely for national broadcasters, international propaganda, or religious broadcasting organizations. Shortwave transmissions can have international or inter-continental range depending on atmospheric conditions. Long-wave AM broadcasting occurs in Europe, Asia, and Africa. The ground wave propagation at these frequencies

7500-467: The country at night. During the night, absorption largely disappears and permits signals to travel to much more distant locations via ionospheric reflections. However, fading of the signal can be severe at night. AM radio transmitters can transmit audio frequencies up to 15 kHz (now limited to 10 kHz in the US due to FCC rules designed to reduce interference), but most receivers are only capable of reproducing frequencies up to 5 kHz or less. At

7625-407: The crystal detector had always been a barrier to its acceptance as a standard component in commercial radio equipment and was one reason for its rapid replacement. Frederick Seitz, an early semiconductor researcher, wrote: Such variability, bordering on what seemed the mystical, plagued the early history of crystal detectors and caused many of the vacuum tube experts of a later generation to regard

SECTION 60

#1732854809869

7750-461: The crystal detector worked. The German word halbleiter , translated into English as " semiconductor ", was first used in 1911 to describe substances whose conductivity fell between conductors and insulators , such as the crystals in crystal detectors. Felix Bloch and Rudolf Peierls around 1930 applied quantum mechanics to create a theory of how electrons move through a crystal. In 1931, Alan Wilson created quantum band theory which explains

7875-408: The crystal surface was needed to make a sensitive rectifying contact. Crystals that required a light pressure like galena were used with the wire cat whisker contact; silicon was used with a heavier point contact, while silicon carbide ( carborundum ) could tolerate the heaviest pressure. Another type used two crystals of different minerals with their surfaces touching, the most common being

8000-451: The development of modern semiconductor diodes finally made the galena cat whisker detector obsolete. Semiconductor devices like the crystal detector work by quantum mechanical principles; their operation cannot be explained by classical physics . The birth of quantum mechanics in the 1920s was the necessary foundation for the development of semiconductor physics in the 1930s, during which physicists arrived at an understanding of how

8125-486: The dominant medium, especially in cities. Because of its greater range, AM remained more common in rural environments. Pirate radio is illegal or non-regulated radio transmission. It is most commonly used to describe illegal broadcasting for entertainment or political purposes. Sometimes it is used for illegal two-way radio operation. Its history can be traced back to the unlicensed nature of the transmission, but historically there has been occasional use of sea vessels—fitting

8250-417: The earphone when the radio wave was present to represent the "dots" and "dashes" of Morse code. The device which did this was called a detector . The crystal detector was the most successful of many detector devices invented during this era. The crystal detector evolved from an earlier device, the first primitive radio wave detector, called a coherer , developed in 1890 by Édouard Branly and used in

8375-416: The earphone. The bias moved the operating point to the curved "knee" of the device's current–voltage curve , which produced the largest rectified current. Patented and first manufactured in 1906 by Pickard, this was the first type of crystal detector to be commercially produced. Silicon required more pressure than the cat whisker contact, although not as much as carborundum. A flat piece of silicon

8500-423: The effect of radio waves on various types of "imperfect" contacts to develop better coherers, invented crystal detectors. The "unilateral conduction" of crystals was discovered by Karl Ferdinand Braun , a German physicist, in 1874 at the University of Würzburg . He studied copper pyrite (Cu 5 FeS 4 ), iron pyrite (iron sulfide, FeS 2 ), galena (PbS) and copper antimony sulfide (Cu 3 SbS 4 ). This

8625-406: The effect. The first person to exploit negative resistance practically was self-taught Russian physicist Oleg Losev , who devoted his career to the study of crystal detectors. In 1922 working at the new Nizhny Novgorod Radio Laboratory he discovered negative resistance in biased zincite ( zinc oxide ) point contact junctions. He realized that amplifying crystals could be an alternative to

8750-414: The electrical conductivity of solids. Werner Heisenberg conceived the idea of a hole , a vacancy in a crystal lattice where an electron should be, which can move about the lattice like a positive particle; both electrons and holes conduct current in semiconductors. A breakthrough came when it was realized that the rectifying action of crystalline semiconductors was not due to the crystal alone but to

8875-399: The electrodes. Before a radio wave was applied, this device had a high electrical resistance , in the megohm range. When a radio wave from the antenna was applied across the electrodes it caused the filings to "cohere" or clump together and the coherer's resistance fell, causing a DC current from a battery to pass through it, which rang a bell or produced a mark on a paper tape representing

9000-501: The explanation of the light emission was in the new science of quantum mechanics , speculating that it was the inverse of the photoelectric effect discovered by Albert Einstein in 1905. He wrote to Einstein about it, but did not receive a reply. Losev designed practical carborundum electroluminescent lights, but found no one interested in commercially producing these weak light sources. Losev died in World War II. Due partly to

9125-708: The fact that his papers were published in Russian and German, and partly to his lack of reputation (his upper class birth barred him from a college education or career advancement in Soviet society, so he never held an official position higher than technician) his work is not well known in the West. In the 1920s, the amplifying triode vacuum tube , invented in 1907 by Lee De Forest , replaced earlier technology in both radio transmitters and receivers. AM radio broadcasting spontaneously arose around 1920, and radio listening exploded to become

9250-466: The first modern diodes. After the war, germanium diodes replaced galena cat whisker detectors in the few crystal radios being made. Germanium diodes are more sensitive than silicon diodes as detectors, because germanium has a lower forward voltage drop than silicon (0.4 vs 0.7 volts). Today a few galena cat whisker detectors are still being made, but only for antique replica crystal radios or devices for science education. Introduced in 1946 by Sylvania,

9375-495: The first practical wireless telegraphy transmitters and receivers in 1896, and radio began to be used for communication around 1899. The coherer was used as detector for the first 10 years, until around 1906. During the wireless telegraphy era prior to 1920, there was virtually no broadcasting ; radio served as a point-to-point text messaging service. Until the triode vacuum tube began to be used around World War I , radio receivers had no amplification and were powered only by

9500-467: The first radio receivers in 1894–96 by Marconi and Oliver Lodge . Made in many forms, the coherer consisted of a high resistance electrical contact, composed of conductors touching with a thin resistive surface film, usually oxidation, between them. Radio waves changed the resistance of the contact, causing it to conduct a DC current. The most common form consisted of a glass tube with electrodes at each end, containing loose metal filings in contact with

9625-472: The first three decades of radio, from 1888 to 1918, called the wireless telegraphy or "spark" era, primitive radio transmitters called spark gap transmitters were used, which generated radio waves by an electric spark . These transmitters were unable to produce the continuous sinusoidal waves which are used to transmit audio (sound) in modern AM or FM radio transmission. Instead spark gap transmitters transmitted information by wireless telegraphy ;

9750-480: The first time created semiconductor junctions with reliable, repeatable characteristics, allowing scientists to test their theories, and later making manufacture of modern diodes possible. The theory of rectification in a metal-semiconductor junction, the type used in a cat whisker detector, was developed in 1938 independently by Walter Schottky at Siemens & Halske research laboratory in Germany and Nevill Mott at Bristol University , UK. Mott received

9875-541: The floor to rock, and military stations where gunfire was expected. In 1907–1909, George Washington Pierce at Harvard conducted research into how crystal detectors worked. Using an oscilloscope made with Braun's new cathode ray tube , he produced the first pictures of the waveforms in a working detector, proving that it did rectify the radio wave. During this era, before modern solid-state physics , most scientists believed that crystal detectors operated by some thermoelectric effect. Although Pierce did not discover

10000-407: The fragile, expensive, energy-wasting vacuum tube. He used biased negative resistance crystal junctions to build solid-state amplifiers , oscillators , and amplifying and regenerative radio receivers , 25 years before the invention of the transistor. Later he even built a superheterodyne receiver . However his achievements were overlooked because of the success of vacuum tubes. His technology

10125-473: The frequency of radio transmitters . The crystal detector consisted of an electrical contact between the surface of a semiconducting crystalline mineral and either a metal or another crystal. Since at the time they were developed no one knew how they worked, crystal detectors evolved by trial and error. The construction of the detector depended on the type of crystal used, as it was found different minerals varied in how much contact area and pressure on

10250-570: The highest and lowest sidebands is quite apparent to the listener. Such distortion occurs up to frequencies of approximately 50 MHz. Higher frequencies do not reflect from the ionosphere, nor from storm clouds. Moon reflections have been used in some experiments, but require impractical power levels. The original FM radio service in the U.S. was the Yankee Network , located in New England . Regular FM broadcasting began in 1939 but did not pose

10375-467: The ionosphere. In a crowded channel environment, this means that the power of regional channels which share a frequency must be reduced at night or directionally beamed in order to avoid interference, which reduces the potential nighttime audience. Some stations have frequencies unshared with other stations in North America; these are called clear-channel stations . Many of them can be heard across much of

10500-436: The mechanism by which it worked, he did prove that the existing theories were wrong; his oscilloscope waveforms showed there was no phase delay between the voltage and current in the detector, ruling out thermal mechanisms. Pierce originated the name crystal rectifier . Between about 1905 and 1915 new types of radio transmitters were developed which produced continuous sinusoidal waves : the arc converter (Poulsen arc) and

10625-443: The mid-1930s George Southworth at Bell Labs , working on this problem, bought an old cat whisker detector and found it worked at microwave frequencies. Hans Hollmann in Germany made the same discovery. The MIT Radiation Laboratory launched a project to develop microwave detector diodes, focusing on silicon, which had the best detecting properties. By about 1942 point-contact silicon crystal detectors for radar receivers such as

10750-402: The most common perception of a pirate—as broadcasting bases. Rules and regulations vary largely from country to country, but often the term pirate radio describes the unlicensed broadcast of FM radio, AM radio, or shortwave signals over a wide range. In some places, radio stations are legal where the signal is transmitted, but illegal where the signals are received—especially when the signals cross

10875-567: The most widely used type among amateurs, became virtually the only detector used in crystal radios from this point on. The carborundum junction saw some use as a detector in early vacuum tube radios because it was more sensitive than the triode grid-leak detector . Crystal radios were kept as emergency backup radios on ships. During World War II in Nazi-occupied Europe the radio saw use as an easily constructed, easily concealed clandestine radio by Resistance groups. After World War II,

11000-486: The new band had to begin from the ground floor. As a commercial venture, it remained a little-used audio enthusiasts' medium until the 1960s. The more prosperous AM stations, or their owners, acquired FM licenses and often broadcast the same programming on the FM station as on the AM station (" simulcasting "). The FCC limited this practice in the 1960s. By the 1980s, since almost all new radios included both AM and FM tuners, FM became

11125-416: The oscillating current induced in the antenna from the desired radio station, and the earphone. Its function was to act as a demodulator , rectifying the radio signal, converting it from alternating current to a pulsing direct current , to extract the audio signal ( modulation ) from the radio frequency carrier wave . An AM demodulator which works in this way, by rectifying the modulated carrier,

11250-703: The other direction, instead of a straight line, showing that these substances did not obey Ohm's law . Due to this characteristic, some crystals had up to twice as much resistance to current in one direction as they did to current in the other. In 1877 and 1878 he reported further experiments with psilomelane , (Ba,H 2 O) 2 Mn 5 O 10 . Braun did investigations which ruled out several possible causes of asymmetric conduction, such as electrolytic action and some types of thermoelectric effects. Thirty years after these discoveries, after Bose's experiments, Braun began experimenting with his crystalline contacts as radio wave detectors. In 1906 he obtained

11375-446: The other direction. The "metallurgical purity" chemicals used by scientists to make synthetic experimental detector crystals had about 1% impurities which were responsible for such inconsistent results. During the 1930s progressively better refining methods were developed, allowing scientists to create ultrapure semiconductor crystals into which they introduced precisely controlled amounts of trace elements (called doping ). This for

11500-424: The presence of impurity atoms in the crystal lattice. In 1930 Bernhard Gudden and Wilson established that electrical conduction in semiconductors was due to trace impurities in the crystal. A "pure" semiconductor did not act as a semiconductor, but as an insulator (at low temperatures). The maddeningly variable activity of different pieces of crystal when used in a detector, and the presence of "active sites" on

11625-666: The productions, they chose to air tunes of their choice in heavy rotation. The station is considered the most popular among the younger generation in Osaka. FM802 was founded in September 1988, going on air in June the following year, with the call sign of JOFV-FM, as one of the first radio stations to sign on in the Heisei era . The station is a member of the Japan FM League (JFL). It operates 24 hours

11750-471: The radio waves are broadcast by a land-based radio station , while in satellite radio the radio waves are broadcast by a satellite in Earth orbit. To receive the content the listener must have a broadcast radio receiver ( radio ). Stations are often affiliated with a radio network that provides content in a common radio format , either in broadcast syndication or simulcast , or both. The encoding of

11875-480: The radio waves picked up by their antennae. Long distance radio communication depended on high power transmitters (up to 1 MW), huge wire antennas, and a receiver with a sensitive detector. Crystal detectors were invented by several researchers at about the same time. Braun began to experiment with crystal detectors around 1899, around when Bose patented his galena detector. Pickard invented his silicon detector in 1906. Also in 1906 Henry Harrison Chase Dunwoody ,

12000-455: The range of a given FM signal was much shorter; thus its market was more local than for AM radio. The reception range at night is the same as in the daytime. All FM broadcast transmissions are line-of-sight, and ionospheric bounce is not viable. The much larger bandwidths, compared to AM and SSB, are more susceptible to phase dispersion. Propagation speeds are fastest in the ionosphere at the lowest sideband frequency. The celerity difference between

12125-485: The resurrection of the point contact crystal detector. Microwave radar receivers required a nonlinear device that could act as a mixer , to mix the incoming microwave signal with a local oscillator signal, to shift the microwave signal down to a lower intermediate frequency (IF) at which it could be amplified. The vacuum tubes used as mixers at lower frequencies in superheterodyne receivers could not function at microwave frequencies due to excessive capacitance. In

12250-470: The reverse direction because the plate was not heated, and thus not capable of thermionic emission of electrons. Later known as the Fleming valve , it could be used as a rectifier of alternating current, and as a radio wave detector . This greatly improved the crystal set , which rectified the radio signal using an early solid-state diode based on a crystal and a so-called cat's whisker . However, an amplifier

12375-410: The same service area. This prevents the sideband power generated by two stations from interfering with each other. Bob Carver created an AM stereo tuner employing notch filtering that demonstrated that an AM broadcast can meet or exceed the 15 kHz baseband bandwidth allotted to FM stations without objectionable interference. After several years, the tuner was discontinued. Bob Carver had left

12500-517: The silicon detector 30 August 1906. In 1907 he formed a company to manufacture his detectors, Wireless Specialty Products Co., and the silicon detector was the first crystal detector to be sold commercially. Pickard went on to produce other detectors using the crystals he had discovered; the more popular being the iron pyrite "Pyron" detector and the zincite – chalcopyrite crystal-to-crystal "Perikon" detector in 1908, which stood for " PER fect p I c K ard c ON tact". Guglielmo Marconi developed

12625-521: The station was moved to the top of the Westinghouse factory building in East Pittsburgh, Pennsylvania . Westinghouse relaunched the station as KDKA on November 2, 1920, as the first commercially licensed radio station in the United States. The commercial broadcasting designation came from the type of broadcast license ; advertisements did not air until years later. The first licensed broadcast in

12750-480: The surface, was due to natural variations in the concentration of these impurities throughout the crystal. Nobel Laureate Walter Brattain , coinventor of the transistor, noted: At that time you could get a chunk of silicon... put a cat whisker down on one spot, and it would be very active and rectify very well in one direction. You moved it around a little bit-maybe a fraction, a thousandth of an inch-and you might find another active spot, but here it would rectify in

12875-408: The time that AM broadcasting began in the 1920s, this provided adequate fidelity for existing microphones, 78 rpm recordings, and loudspeakers. The fidelity of sound equipment subsequently improved considerably, but the receivers did not. Reducing the bandwidth of the receivers reduces the cost of manufacturing and makes them less prone to interference. AM stations are never assigned adjacent channels in

13000-450: The time, the electrolytic detector , Fleming valve and the triode could also rectify AM signals, crystals were the simplest, cheapest AM detector. As more and more radio stations began experimenting with transmitting sound after World War I, a growing community of radio listeners built or bought crystal radios to listen to them. Use continued to grow until the 1920s when vacuum tube radios replaced them. Some semiconductor diodes have

13125-416: The time. This detector was also sometimes used with a small forward bias voltage of around 0.2V from a battery to make it more sensitive. Although the zincite-chalcopyrite "Perikon" was the most widely used crystal-to-crystal detector, other crystal pairs were also used. Zincite was used with carbon, galena, and tellurium . Silicon was used with arsenic , antimony and tellurium crystals. During

13250-466: The trade name carborundum ), either clamped between two flat metal contacts, or mounted in fusible alloy in a metal cup with a contact consisting of a hardened steel point pressed firmly against it with a spring. Carborundum, an artificial product of electric furnaces produced in 1893, required a heavier pressure than the cat whisker contact. The carborundum detector was popular because its sturdy contact did not require readjustment each time it

13375-449: The user turned the transmitter on and off rapidly by tapping on a telegraph key , producing pulses of radio waves which spelled out text messages in Morse code . Therefore, the radio receivers of this era did not have to demodulate the radio wave, extract an audio signal from it as modern receivers do, they merely had to detect the presence or absence of the radio waves, to make a sound in

13500-421: The way the eye detected light, and Bose found his detector was also sensitive to visible light and ultraviolet, leading him to call it an artificial retina . He patented the detector 30 September 1901. This is often considered the first patent on a semiconductor device. Greenleaf Whittier Pickard may be the person most responsible for making the crystal detector a practical device. Pickard, an engineer with

13625-409: The wire into the crystal but not in the other direction. Only certain sites on the crystal surface functioned as rectifying junctions. The device was very sensitive to the exact geometry and pressure of contact between wire and crystal, and the contact could be disrupted by the slightest vibration. Therefore, a usable point of contact had to be found by trial and error before each use. The wire

13750-557: The world. Many stations broadcast on shortwave bands using AM technology that can be received over thousands of miles (especially at night). For example, the BBC , VOA , VOR , and Deutsche Welle have transmitted via shortwave to Africa and Asia. These broadcasts are very sensitive to atmospheric conditions and solar activity. Nielsen Audio , formerly known as Arbitron, the United States –based company that reports on radio audiences, defines

13875-400: Was zincite ( zinc oxide , ZnO), the other was a copper iron sulfide, either bornite (Cu 5 FeS 4 ) or chalcopyrite (CuFeS 2 ). In Pickard's commercial detector (see picture) , multiple zincite crystals were mounted in a fusible alloy in a round cup (on right) , while the chalcopyrite crystal was mounted in a cup on an adjustable arm facing it (on left) . The chalcopyrite crystal

14000-429: Was acting as a rectifier. During the next four years, Pickard conducted an exhaustive search to find which substances formed the most sensitive detecting contacts, eventually testing thousands of minerals, and discovered about 250 rectifying crystals. In 1906 he obtained a sample of fused silicon , an artificial product recently synthesized in electric furnaces, and it outperformed all other substances. He patented

14125-517: Was amalgamated in 1922 and received a Royal Charter in 1926, making it the first national broadcaster in the world, followed by Czechoslovak Radio and other European broadcasters in 1923. Radio Argentina began regularly scheduled transmissions from the Teatro Coliseo in Buenos Aires on August 27, 1920, making its own priority claim. The station got its license on November 19, 1923. The delay

14250-424: Was before radio waves had been discovered, and Braun did not apply these devices practically but was interested in the nonlinear current–voltage characteristic that these sulfides exhibited. Graphing the current as a function of voltage across a contact made by a piece of mineral touched by a wire cat whisker, he found the result was a line that was flat for current in one direction but curved upward for current in

14375-500: Was carrying audio by the next year. (Herrold's station eventually became KCBS ). In The Hague, the Netherlands, PCGG started broadcasting on November 6, 1919, making it arguably the first commercial broadcasting station. In 1916, Frank Conrad , an electrical engineer employed at the Westinghouse Electric Corporation , began broadcasting from his Wilkinsburg, Pennsylvania garage with the call letters 8XK. Later,

14500-408: Was dubbed "Crystodyne" by science publisher Hugo Gernsback one of the few people in the West who paid attention to it. After ten years he abandoned research into this technology and it was forgotten. The negative resistance diode was rediscovered with the invention of the tunnel diode in 1957, for which Leo Esaki won the 1973 Nobel Prize in Physics . Today, negative resistance diodes such as

14625-456: Was due to the lack of official Argentine licensing procedures before that date. This station continued regular broadcasting of entertainment, and cultural fare for several decades. Radio in education soon followed, and colleges across the U.S. began adding radio broadcasting courses to their curricula. Curry College in Milton, Massachusetts introduced one of the first broadcasting majors in 1932 when

14750-431: Was embedded in fusible alloy in a metal cup, and a metal point, usually brass or gold , was pressed against it with a spring. The surface of the silicon was usually ground flat and polished. Silicon was also used with antimony and arsenic contacts. The silicon detector was popular because it had much the same advantages as carborundum; its firm contact could not be jarred loose by vibration and it did not require

14875-436: Was moved forward until it touched the surface of one of the zincite crystals. When a sensitive spot was located, the arm was locked in place with the setscrew. Multiple zincite pieces were provided because the fragile zincite crystal could be damaged by excessive currents and tended to "burn out" due to atmospheric electricity from the wire antenna or currents leaking into the receiver from the powerful spark transmitters used at

15000-531: Was quickly becoming viable. However, an early audio transmission that could be termed a broadcast may have occurred on Christmas Eve in 1906 by Reginald Fessenden , although this is disputed. While many early experimenters attempted to create systems similar to radiotelephone devices by which only two parties were meant to communicate, there were others who intended to transmit to larger audiences. Charles Herrold started broadcasting in California in 1909 and

15125-487: Was still required. The triode (mercury-vapor filled with a control grid) was created on March 4, 1906, by the Austrian Robert von Lieben ; independently, on October 25, 1906, Lee De Forest patented his three-element Audion . It was not put to practical use until 1912 when its amplifying ability became recognized by researchers. By about 1920, valve technology had matured to the point where radio broadcasting

15250-427: Was suspended from a moveable arm and was dragged across the crystal face by the user until the device began functioning. In a crystal radio, the user would tune the radio to a strong local station if possible and then adjust the cat whisker until the station or radio noise (a static hissing noise) was heard in the radio's earphones. This required some skill and a lot of patience. An alternative method of adjustment

15375-563: Was to find rectifying crystals that were less fragile and sensitive to vibration than galena and pyrite. Another desired property was tolerance of high currents; many crystals would become insensitive when subjected to discharges of atmospheric electricity from the outdoor wire antenna, or current from the powerful spark transmitter leaking into the receiver. Carborundum proved to be the best of these; it could rectify when clamped firmly between flat contacts. Therefore, carborundum detectors were used in shipboard wireless stations where waves caused

15500-418: Was to use a battery-operated electromechanical buzzer connected to the radio's ground wire or inductively coupled to the tuning coil, to generate a test signal. The spark produced by the buzzer's contacts functioned as a weak radio transmitter whose radio waves could be received by the detector, so when a rectifying spot had been found on the crystal the buzz could be heard in the earphones, at which time

15625-483: Was used, like the delicate cat whisker devices. Some carborundum detectors were adjusted at the factory and then sealed and did not require adjustment by the user. It was not sensitive to vibration and so was used in shipboard wireless stations where the ship was rocked by waves, and military stations where vibration from gunfire could be expected. Another advantage was that it was tolerant of high currents, and could not be "burned out" by atmospheric electricity from

#868131