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113-495: Audions had more residual gas than later vacuum tubes; the residual gas limited the dynamic range and gave the Audion non-linear characteristics and erratic performance. Originally developed as a radio receiver detector by adding a grid electrode to the Fleming valve , it found little use until its amplifying ability was recognized around 1912 by several researchers, who used it to build

226-467: A discharge tube or formerly as a Plücker tube , is an arrangement of electrodes in a gas within an insulating , temperature-resistant envelope . Gas-filled tubes exploit phenomena related to electric discharge in gases , and operate by ionizing the gas with an applied voltage sufficient to cause electrical conduction by the underlying phenomena of the Townsend discharge . A gas-discharge lamp

339-510: A 22–volt battery via a pair of headphones, the negative terminal being connected to one side of the lamp filament. When wireless signals were applied to the wire wrapped around the outside of the glass, they caused disturbances in the current which produced sounds in the headphones. This was a significant development as existing commercial wireless systems were heavily protected by patents ; a new type of detector would allow de Forest to market his own system. He eventually discovered that connecting

452-569: A Kenotron, since that was somewhat easier to stabilize. He soon realized that his "vacuum" Audion had markedly different characteristics from the de Forest version, and was really a quite different device, capable of linear amplification and at much higher frequencies. To distinguish his device from the Audion he named it the "Pliotron", from the Greek plio (more or extra, in this sense meaning gain , more signal coming out than went in). Essentially, he referred to all his vacuum tube designs as Kenotrons,

565-404: A band from 42 to 50 MHz, with the first five channels reserved for educational stations. Existing Apex stations were notified that they would not be allowed to operate after January 1, 1941, unless they converted to FM. Although there was interest in the new FM band by station owners, construction restrictions that went into place during WWII limited the growth of the new service. Following

678-501: A demonstration of his regeneration receiver in 1913, about the corporation offering superheterodynes as a superior offering to the general public. (The ongoing patent dispute was not a hindrance, because extensive cross-licensing agreements signed in 1920 and 1921 between RCA, Westinghouse and AT&T meant that Armstrong could freely use the Lévy patent.) Superheterodyne sets were initially thought to be prohibitively complicated and expensive as

791-617: A detailed mathematical analysis which showed that FM transmissions did not provide any improvement over AM. Although the Carson bandwidth rule for FM is important today, Carson's review turned out to be incomplete, as it analyzed only (what is now known as) "narrow-band" FM. In early 1928 Armstrong began researching the capabilities of FM. Although there were others involved in FM research at this time, he knew of an RCA project to see if FM shortwave transmissions were less susceptible to fading than AM. In 1931

904-416: A filament made from a hydrogen-absorbing metal (e.g. zirconium or titanium) is present in the tube, and by controlling its temperature the ratio of absorbed and desorbed hydrogen is adjusted, resulting in controlling of the hydrogen pressure in the tube. The metal filament acts as a hydrogen storage. This approach is used in e.g. hydrogen thyratrons or neutron tubes. Usage of saturated mercury vapor allows using

1017-451: A fireplace poker, striking her on the arm. She left their apartment to stay with her sister. Sometime during the night of January 31 – February 1, 1954, Armstrong jumped to his death from a window in his 12-room apartment on the 13th floor of River House in Manhattan , New York City . The New York Times described the contents of his two-page suicide note to his wife: "he

1130-527: A keen interest in gaining a detailed scientific understanding of how vacuum tubes worked. In conjunction with Professor Morecroft he used an oscillograph to conduct comprehensive studies. His breakthrough discovery was determining that employing positive feedback (also known as "regeneration" ) produced amplification hundreds of times greater than previously attained, with the amplified signals now strong enough so that receivers could use loudspeakers instead of headphones. Further investigation revealed that when

1243-424: A locally generated, different frequency signal within a radio set. That circuit is called the mixer. The result is a fixed, unchanging intermediate frequency, or I.F. signal which is easily amplified and detected by following circuit stages. In 1919, Armstrong filed an application for a US patent of the superheterodyne circuit which was issued the next year. This patent was subsequently sold to Westinghouse. The patent

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1356-590: A makeshift backyard antenna tower that included a bosun's chair for hoisting himself up and down its length, to the concern of neighbors. Much of his early research was conducted in the attic of his parents' house. In 1909, Armstrong enrolled at Columbia University in New York City, where he became a member of the Epsilon Chapter of the Theta Xi engineering fraternity, and studied under Professor Michael Pupin at

1469-619: A noise source, when operated as a diode in a transverse magnetic field. In the mid-20th century, voltage-regulator tubes were commonly used. Cathode sputtering is taken advantage of in the Time Totalizer , a metal-vapor coulometer -based elapsed time meter where the sputtered metal is deposited on a collector element whose resistance therefore decreases slowly. Edwin Howard Armstrong Edwin Howard Armstrong (December 18, 1890 – February 1, 1954 )

1582-523: A non-exclusive, royalty-free license to use his FM patents. He refused this offer, because he felt this would be unfair to the other licensed companies, which had to pay 2% royalties on their sales. Over time this impasse with RCA dominated Armstrong's life. RCA countered by conducting its own FM research, eventually developing what it claimed was a non-infringing FM system. The corporation encouraged other companies to stop paying royalties to Armstrong. Outraged by this, in 1948 Armstrong filed suit against RCA and

1695-469: A normal bayonet light bulb mount for the filament and an anode top cap , for SHF frequencies and diagonal insertion into a waveguide . They were filled with a pure inert gas such as neon because mixtures made the output temperature-dependent. Their burning voltage was under 200 V, but they needed optical priming by an incandescent 2-watt lamp and a voltage surge in the 5-kV range for ignition. One miniature thyratron found an additional use as

1808-402: A pool of liquid mercury as a large storage of material; the atoms lost by clean-up are automatically replenished by evaporation of more mercury. The pressure in the tube is however strongly dependent on the mercury temperature, which has to be controlled carefully. Large rectifiers use saturated mercury vapor with a small amount of an inert gas. The inert gas supports the discharge when the tube

1921-407: A small piece of galena crystal probed by a fine wire commonly referred to as a " cat's-whisker detector ". They were very unreliable, requiring frequent adjustment of the cat's whisker and offered no amplification. Such systems usually required the user to listen to the signal through headphones, sometimes at very low volume, as the only energy available to operate the headphones was that picked up by

2034-622: A statement that it "strongly affirms the original award". The United States entered WWI in April 1917. Later that year Armstrong was commissioned as a captain in the U.S. Army Signal Corps , and assigned to a laboratory in Paris, France to help develop radio communication for the Allied war effort. He returned to the US in the autumn of 1919, after being promoted to the rank of Major. (During both world wars, Armstrong gave

2147-400: A vacuum) and tron (device, instrument). He then turned his attention to the Audion tube, again suspecting that its notoriously unpredictable behaviour might be tamed with more care in the manufacturing process. However he took a somewhat unorthodox approach. Instead of trying to stabilize the partial vacuum, he wondered if it was possible to make the Audion function with the total vacuum of

2260-453: A visiting professor from Cornell University that he disliked into receiving a severe electrical shock. He also stressed the practical over the theoretical, stating that progress was more likely the product of experimentation and reasoning than on mathematical calculation and the formulae of " mathematical physics ". Armstrong graduated from Columbia in 1913, earning an electrical engineering degree. During World War I , Armstrong served in

2373-412: Is an electric light using a gas-filled tube; these include fluorescent lamps , metal-halide lamps , sodium-vapor lamps , and neon lights . Specialized gas-filled tubes such as krytrons , thyratrons , and ignitrons are used as switching devices in electric devices. The voltage required to initiate and sustain discharge is dependent on the pressure and composition of the fill gas and geometry of

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2486-469: Is cold. The mercury arc valve current-voltage characteristics are highly dependent on the temperature of the liquid mercury. The voltage drop in forward bias decreases from about 60 volts at 0 °C to somewhat above 10 volts at 50 °C and then stays constant; the reverse bias breakdown ("arc-back") voltage drops dramatically with temperature, from 36 kV at 60 °C to 12 kV at 80 °C to even less at higher temperatures. The operating range

2599-491: Is highly electronegative and inhibits the production of electron avalanches. This makes the discharge look pale, milky, or reddish. Traces of mercury vapors glow bluish, obscuring the original gas color. Magnesium vapor colors the discharge green. To prevent outgassing of the tube components during operation, a bake-out is required before filling with gas and sealing. Thorough degassing is required for high-quality tubes; even as little as 10  torr (≈1 μPa) of oxygen

2712-404: Is however about 40% slower than for hydrogen. Noble gases are frequently used in tubes for many purposes, from lighting to switching. Pure noble gases are employed in switching tubes. Noble-gas-filled thyratrons have better electrical parameters than mercury-based ones. The electrodes undergo damage by high-velocity ions. The neutral atoms of the gas slow the ions down by collisions, and reduce

2825-570: Is not neon based these days) are also low-pressure gas-filled tubes. Specialized historic low-pressure gas-filled tube devices include the Nixie tube (used to display numerals) and the Decatron (used to count or divide pulses, with display as a secondary function). Xenon flash lamps are gas-filled tubes used in cameras and strobe lights to produce bright flashes of light. The recently developed sulfur lamps are also gas-filled tubes when hot. Since

2938-598: Is still extensively used by radio equipment. Eighty years after its invention, FM technology has started to be supplemented, and in some cases replaced, by more efficient digital technologies. The introduction of digital television eliminated the FM audio channel that had been used by analog television, HD Radio has added digital sub-channels to FM band stations, and, in Europe and Pacific Asia, Digital Audio Broadcasting bands have been created that will, in some cases, eliminate existing FM stations altogether. However, FM broadcasting

3051-468: Is still used internationally, and remains the dominant system employed for audio broadcasting services. In 1923, combining his love for high places with courtship rituals, Armstrong climbed the WJZ (now WABC) antenna located atop a 20-story building in New York City, where he reportedly did a handstand, and when a witness asked him what motivated him to "do these damnfool things", Armstrong replied "I do it because

3164-449: Is sufficient for covering the electrodes with monomolecular oxide layer in few hours. Non-inert gases can be removed by suitable getters . For mercury-containing tubes, getters that do not form amalgams with mercury (e.g. zirconium , but not barium ) have to be used. Cathode sputtering may be used intentionally for gettering non-inert gases; some reference tubes use molybdenum cathodes for this purpose. Pure inert gases are used where

3277-418: Is therefore usually between 18–65 °C. The gas in the tube has to be kept pure to maintain the desired properties; even small amount of impurities can dramatically change the tube values. The presence of non-inert gases generally increases the breakdown and burning voltages. The presence of impurities can be observed by changes in the glow color of the gas. Air leaking into the tube introduces oxygen, which

3390-464: Is used instead of hydrogen where high voltage operation is required. For a comparison, the hydrogen-filled CX1140 thyratron has anode voltage rating of 25 kV, while the deuterium-filled and otherwise identical CX1159 has 33 kV. Also, at the same voltage the pressure of deuterium can be higher than of hydrogen, allowing higher rise rates of current before it causes excessive anode dissipation. Significantly higher peak powers are achievable. Its recovery time

3503-457: The Apex band , consisting of 75 broadcasting frequencies from 41.02 to 43.98 MHz. As on the standard broadcast band, these were AM stations but with higher quality audio – in one example, a frequency response from 20 Hz to 17,000 Hz +/- 1 dB – because station separations were 40 kHz instead of the 10 kHz spacings used on the original AM band. Armstrong worked to convince

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3616-608: The Great Depression . Making existing AM radio transmitters and receivers obsolete would necessitate that stations buy replacement transmitters and listeners purchase FM-capable receivers. In 1936 he published a landmark paper in the Proceedings of the IRE that documented the superior capabilities of using wide-band FM. (This paper would be reprinted in the August 1984 issue of Proceedings of

3729-532: The Signal Corps as a captain and later a major. Following college graduation, he received a $ 600 one-year appointment as a laboratory assistant at Columbia, after which he nominally worked as a research assistant, for a salary of $ 1 a year, under Professor Pupin. Unlike most engineers, Armstrong never became a corporate employee. He set up a self-financed independent research and development laboratory at Columbia, and owned his patents outright. In 1934, he filled

3842-641: The U.S. Army Signal Corps during World War I and was often referred to as "Major Armstrong" during his career. He was inducted into the National Inventors Hall of Fame and included in the International Telecommunication Union 's roster of great inventors. He was inducted into the Wireless Hall of Fame posthumously in 2001. Armstrong attended Columbia University, and served as a professor there for most of his life. Armstrong

3955-639: The negative differential resistance -region can be exploited to realize timers, relaxation oscillators and digital circuits with neon lamps , trigger tubes , relay tubes , dekatrons and nixie tubes . Thyratrons can also be used as triodes by operating them below their ignition voltage, allowing them to amplify analog signals as a self-quenching superregenerative detector in radio control receivers. There were special neon lamps besides nixie tubes: Hot-cathode , gas-discharge noise diodes were available in normal radio tube glass envelopes for frequencies up to UHF , and as long, thin glass tubes with

4068-495: The "triode" (three-electrode) version was patented in 1908 ( U.S. patent 879,532 ). De Forest continued to claim that he developed the Audion independently from John Ambrose Fleming 's earlier research on the thermionic valve (for which Fleming received Great Britain patent 24850 and the American Fleming valve patent U.S. patent 803,684 ), and de Forest became embroiled in many radio-related patent disputes. De Forest

4181-470: The 85th floor of the Empire State Building in New York City. An antenna attached to the building's spire transmitted signals for distances up to 80 miles (130 km). These tests helped demonstrate FM's static-reduction and high-fidelity capabilities. RCA, which was heavily invested in perfecting TV broadcasting, chose not to invest in FM, and instructed Armstrong to remove his equipment. Denied

4294-423: The Audion was essential to its operation (Audion being a contraction of "Audio-Ion"), and in fact early Audions had severe reliability problems due to this gas being adsorbed by the metal electrodes. The Audions sometimes worked extremely well; at other times they would barely work at all. As well as de Forest himself, numerous researchers had tried to find ways to improve the reliability of the device by stabilizing

4407-545: The Communists as fast as they could be developed". Following her husband's death, Marion Armstrong took charge of pursuing his estate's legal cases. In late December 1954, it was announced that through arbitration a settlement of "approximately $ 1,000,000" had been made with RCA. Dana Raymond of Cravath, Swaine & Moore in New York served as counsel in that litigation. Marion Armstrong was able to formally establish Armstrong as

4520-501: The Evans staff took up the possibility of bouncing radar signals off the moon. Calculations showed that standard pulsed radar like the stock SCR-271 would not do the job; higher average power, much wider transmitter pulses, and very narrow receiver bandwidth would be required. They realized that the Armstrong equipment could be modified to accomplish the task. The FM modulator of the transmitter

4633-517: The FCC that a band of FM broadcasting stations would be a superior approach. That year he financed the construction of the first FM radio station, W2XMN (later KE2XCC ) at Alpine, New Jersey. FCC engineers had believed that transmissions using high frequencies would travel little farther than line-of-sight distances, limited by the horizon. When operating with 40 kilowatts on 42.8 MHz, the station could be clearly heard 100 miles (160 km) away, matching

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4746-556: The FCC's FM Non-Duplication Rule , which limited large-city broadcasters with AM and FM licenses to simulcasting on those two frequencies for only half of their broadcast hours. Armstrong's FM system was also used for communications between NASA and the Apollo program astronauts. A US Postage Stamp was released in his honor in 1983 in a series commemorating American Inventors. Armstrong has been called "the most prolific and influential inventor in radio history". The superheterodyne process

4859-672: The FM band shift was an economic setback, there was reason for optimism. A book published in 1946 by Charles A. Siepmann heralded FM stations as "Radio's Second Chance". In late 1945, Armstrong contracted with John Orr Young, founding member of the public relations firm Young & Rubicam , to conduct a national campaign promoting FM broadcasting, especially by educational institutions. Article placements promoting both Armstrong personally and FM were made with general circulation publications including The Nation , Fortune , The New York Times , Atlantic Monthly , and The Saturday Evening Post . In 1940, RCA offered Armstrong $ 1,000,000 for

4972-477: The Hartley Laboratories, a separate research unit at Columbia. Another of his instructors, Professor John H. Morecroft, later remembered Armstrong as being intensely focused on the topics that interested him, but somewhat indifferent to the rest of his studies. Armstrong challenged conventional wisdom and was quick to question the opinions of both professors and peers. In one case, he recounted how he tricked

5085-460: The IEEE .) A year later, a paper by Murray G. Crosby (inventor of Crosby system for FM Stereo) in the same journal provided further analysis of the wide-band FM characteristics, and introduced the concept of "threshold", demonstrating that there is a superior signal-to-noise ratio when the signal is stronger than a certain level. In June 1936, Armstrong gave a formal presentation of his new system at

5198-523: The NBC radio network, plus the other major networks including CBS, ABC and Mutual. The change was thought to have been favored by AT&T, as the elimination of FM relaying stations would require radio stations to lease wired links from that company. Particularly galling was the FCC assignment of TV channel 1 to the 44–50 MHz segment of the old FM band. Channel 1 was later deleted, since periodic radio propagation would make local TV signals unviewable. Although

5311-672: The National Broadcasting Company, accusing them of patent infringement and that they had "deliberately set out to oppose and impair the value" of his invention, for which he requested treble damages. Although he was confident that this suit would be successful and result in a major monetary award, the protracted legal maneuvering that followed eventually began to impair his finances, especially after his primary patents expired in late 1950. During World War II, Armstrong turned his attention to investigations of continuous-wave FM radar funded by government contracts. Armstrong hoped that

5424-481: The Pliotron basically being a specialized type of Kenotron. However, because Pliotron and Kenotron were registered trademarks, technical writers tended to use the more generic term "vacuum tube". By the mid-1920s, the term "Kenotron" had come to exclusively refer to vacuum tube rectifiers, while the term "Pliotron" had fallen into disuse. Ironically, in popular usage, the sound-alike brands "Radiotron" and "Ken-Rad" outlasted

5537-542: The RCA engineers constructed a successful FM shortwave link transmitting the Schmeling– Stribling fight broadcast from California to Hawaii, and noted at the time that the signals seemed to be less affected by static. The project made little further progress. Working in secret in the basement laboratory of Columbia's Philosophy Hall , Armstrong developed "wide-band" FM, in the process discovering significant advantages over

5650-527: The US Federal Communications Commission (FCC) headquarters. For comparison, he played a jazz record using a conventional AM radio, then switched to an FM transmission. A United Press correspondent was present, and recounted in a wire service report that: "if the audience of 500 engineers had shut their eyes they would have believed the jazz band was in the same room. There were no extraneous sounds." Moreover, "Several engineers said after

5763-411: The US military free use of his patents.) During this period, Armstrong's most significant accomplishment was the development of a "supersonic heterodyne" – soon shortened to "superheterodyne" – radio receiver circuit. This circuit made radio receivers more sensitive and selective and is used extensively today. The key feature of the superheterodyne approach is the mixing of the incoming radio signal with

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5876-549: The US rights to Lévy's patent and contested Armstrong's grant. The subsequent court reviews continued until 1928, when the District of Columbia Court of Appeals disallowed all nine claims of Armstrong's patent, assigning priority for seven of the claims to Lévy, and one each to Ernst Alexanderson of General Electric and Burton W. Kendall of Bell Laboratories . Although most early radio receivers used regeneration Armstrong approached RCA's David Sarnoff , whom he had known since giving

5989-492: The accelerated ions can penetrate into the electrode materials. New surfaces, formed by sputtering of the electrodes and deposited on e.g. the inner surfaces of the tube, also readily adsorb gases. Non-inert gases can also chemically react with the tube components. Hydrogen may diffuse through some metals. For removal of gas in vacuum tubes , getters are used. For resupplying gas for gas-filled tubes, replenishers are employed. Most commonly, replenishers are used with hydrogen;

6102-663: The age of 81. She was survived by two nephews and a niece. In 1917, Armstrong was the first recipient of the IRE 's (now IEEE) Medal of Honor . For his wartime work on radio, the French government gave him the Legion of Honor in 1919. He was awarded the 1941 Franklin Medal, and in 1942 received the AIEEs Edison Medal "for distinguished contributions to the art of electric communication, notably

6215-497: The amplified output of one triode into the grid of the next, eventually providing more than enough power to drive a full-sized speaker. Apart from this, they were able to amplify the incoming radio signals prior to the detection process, making it work much more efficiently. Vacuum tubes could also be used to make superior radio transmitters . The combination of much more efficient transmitters and much more sensitive receivers revolutionized radio communication during World War I . By

6328-473: The antenna circuit to a third electrode placed directly in the space current path greatly improved the sensitivity; in his earliest versions, this was simply a piece of wire bent into the shape of a gridiron (hence grid ). The Audion provided power gain; with other detectors, all of the power to operate the headphones had to come from the antenna circuit itself. Consequently, weak transmitters could be heard at greater distances. De Forest and everybody else at

6441-441: The antenna. For long distance communication huge antennas were normally required, and enormous amounts of electrical power had to be fed into the transmitter. The Audion was a considerable improvement on this, but the original devices could not provide any subsequent amplification to what was produced in the signal detection process. The later vacuum triodes allowed the signal to be amplified to any desired level, typically by feeding

6554-555: The church moved north, the Smiths and Armstrongs followed, and in 1895 the Armstrong family moved from their brownstone row house at 347 West 29th Street to a similar house at 26 West 97th Street in the Upper West Side . The family was comfortably middle class. At the age of eight, Armstrong contracted Sydenham's chorea (then known as St. Vitus' Dance ), an infrequent but serious neurological disorder precipitated by rheumatic fever. For

6667-608: The commercial rights to his work. Although the obvious candidate was the Radio Corporation of America (RCA), on October 5, 1920, the Westinghouse Electric & Manufacturing Company took out an option for $ 335,000 for the commercial rights for both the regenerative and superheterodyne patents, with an additional $ 200,000 to be paid if Armstrong prevailed in the regenerative patent dispute. Westinghouse exercised this option on November 4, 1920. Legal proceedings related to

6780-468: The daytime coverage of a full power 50-kilowatt AM station. FCC studies comparing the Apex station transmissions with Armstrong's FM system concluded that his approach was superior. In early 1940, the FCC held hearings on whether to establish a commercial FM service. Following this review, the FCC announced the establishment of an FM band effective January 1, 1941, consisting of forty 200 kHz-wide channels on

6893-426: The demonstration that they consider Dr. Armstrong's invention one of the most important radio developments since the first earphone crystal sets were introduced." Armstrong was quoted as saying he could "visualize a time not far distant when the use of ultra-high frequency wave bands will play the leading role in all broadcasting", although the article noted that "A switchover to the ultra-high frequency system would mean

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7006-549: The difference between the ignition voltage and the burning voltage has to be high, e.g. in switching tubes. Tubes for indication and stabilization, where the difference has to be lower, tend to be filled with Penning mixtures ; the lower difference between ignition and burning voltages allows using lower power supply voltages and smaller series resistances. Fluorescent lighting , CFL lamps , mercury and sodium discharge lamps and HID lamps are all gas-filled tubes used for lighting. Neon lamps and neon signage (most of which

7119-460: The discharge channel. One of the most popular choices is sulfur hexafluoride , used in special high-voltage applications. Other common options are dry pressurized nitrogen and halocarbons . The fundamental mechanism is the Townsend discharge, which is the sustained multiplication of electron flow by ion impact when a critical value of electric field strength for the density of the gas is reached. As

7232-416: The earlier "narrow-band" FM transmissions. In a "wide-band" FM system , the deviations of the carrier frequency are made to be much larger than the frequency of the audio signal which can be shown to provide better noise rejection. He was granted five US patents covering the basic features of the new system on December 26, 1933. Initially, the primary claim was that his FM system was effective at filtering out

7345-472: The electric field is increased various phases of discharge are encountered as shown in the accompanying plot. The gas used dramatically influences the parameters of the tube. The breakdown voltage depends on the gas composition and electrode distance; the dependencies are described by Paschen's law . The gas pressure may range between 0.001 and 1,000 Torr (0.13–130,000 Pa); most commonly, pressures between 1–10 torr are used. The gas pressure influences

7458-699: The electrical principles of the Audion. Armstrong published his explanation of the Audion in Electrical World in December 1914, complete with circuit diagrams and oscilloscope graphs. In March and April 1915, Armstrong spoke to the Institute of Radio Engineers in New York and Boston, respectively, presenting his paper "Some Recent Developments in the Audion Receiver", which was published in September. A combination of

7571-412: The end of WWII, the FCC moved to standardize its frequency allocations. One area of concern was the effects of tropospheric and Sporadic E propagation , which at times reflected station signals over great distances, causing mutual interference. A particularly controversial proposal, spearheaded by RCA, was that the FM band needed to be shifted to higher frequencies to avoid this problem. This reassignment

7684-415: The energy transferred to the electrodes by the ion impact. Gases with high molecular weight, e.g. xenon, protect the electrodes better than lighter ones, e.g. neon. In special cases (e.g., high-voltage switches), gases with good dielectric properties and very high breakdown voltages are needed. Highly electronegative elements, e.g., halogens , are favored as they rapidly recombine with the ions present in

7797-416: The feedback was increased beyond a certain level a vacuum-tube would go into oscillation , thus could also be used as a continuous-wave radio transmitter. Beginning in 1913 Armstrong prepared a series of comprehensive demonstrations and papers that carefully documented his research, and in late 1913 applied for patent protection covering the regenerative circuit. On October 6, 1914, U.S. patent 1,113,149

7910-426: The first amplifying radio receivers and electronic oscillators . The many practical applications for amplification motivated its rapid development, and the original Audion was superseded within a few years by improved versions with a higher vacuum. It had been known since the middle of the 19th century that gas flames were electrically conductive , and early wireless experimenters had noticed that this conductivity

8023-424: The following factors: Above a certain value, the higher the gas pressure, the higher the ignition voltage. High-pressure lighting tubes can require a few kilovolts impulse for ignition when cold, when the gas pressure is low. After warming up, when the volatile compound used for light emission is vaporized and the pressure increases, reignition of the discharge requires either significantly higher voltage or reducing

8136-503: The ignition voltage depends on the ion concentration which may drop to zero after a long period of inactivity, many tubes are primed for ion availability: Some important examples include the thyratron , krytron , and ignitron tubes, which are used to switch high-voltage currents. A specialized type of gas-filled tube called a Gas Discharge Tube (GDT) is fabricated for use as surge protectors , to limit voltage surges in electrical and electronic circuits. The Schmitt trigger effect of

8249-538: The initial designs required multiple tuning knobs and used nine vacuum tubes. In conjunction with RCA engineers, Armstrong developed a simpler, less costly design. RCA introduced its superheterodyne Radiola sets in the US market in early 1924, and they were an immediate success, dramatically increasing the corporation's profits. These sets were considered so valuable that RCA would not license the superheterodyne to other US companies until 1930. The regeneration legal battle had one serendipitous outcome for Armstrong. While he

8362-467: The interference fighting characteristic of wide-band FM and a narrow receiver bandwidth to reduce noise would increase range. Primary development took place at Armstrong's Alpine, NJ laboratory. A duplicate set of equipment was sent to the U.S. Army's Evans Signal Laboratory. The results of his investigations were inconclusive, the war ended, and the project was dropped by the Army. Under the name Project Diana ,

8475-399: The internal pressure by cooling down the lamp. For example, many sodium vapor lamps cannot be re-lit immediately after being shut off; they must cool down before they can be lit up again. The gas tends to be used up during the tube operation, by several phenomena collectively called clean-up . The gas atoms or molecules are adsorbed on the surfaces of the electrodes. In high voltage tubes,

8588-510: The inventor of FM following protracted court proceedings over five of his basic FM patents, with a series of successful suits, which lasted until 1967, against other companies that were found guilty of infringement. It was not until the 1960s that FM stations in the United States started to challenge the popularity of the AM band, helped by the development of FM stereo by General Electric, followed by

8701-431: The junking of present broadcasting equipment and present receivers in homes, eventually causing the expenditure of billions of dollars." In the late 1930s, as technical advances made it possible to transmit on higher frequencies, the FCC investigated options for increasing the number of broadcasting stations, in addition to ideas for better audio quality, known as "high-fidelity". In 1937 it introduced what became known as

8814-624: The late 1920s such "tube radios" began to become a fixture of most Western world households, and remained so until long after the introduction of transistor radios in the mid-1950s. In modern electronics , the vacuum tube has been largely superseded by solid state devices such as the transistor , invented in 1947 and implemented in integrated circuits in 1959, although vacuum tubes remain to this day in such applications as high-powered transmitters, guitar amplifiers and some high fidelity audio equipment. Application images Gas-filled tube A gas-filled tube , also commonly known as

8927-427: The law firm of Pennie, Davis, Martin and Edmonds. To finance his legal expenses he began issuing non-transferable licenses for use of the regenerative patents to a select group of small radio equipment firms, and by November 1920, 17 companies had been licensed. These licensees paid 5% royalties on their sales which were restricted to only "amateurs and experimenters". Meanwhile, Armstrong explored his options for selling

9040-550: The legal proceeding twice went before the US Supreme Court, in 1928 and 1934, he was unsuccessful in overturning the decision. In response to the second Supreme Court decision upholding de Forest as the inventor of regeneration, Armstrong attempted to return his 1917 IRE Medal of Honor, which had been awarded "in recognition of his work and publications dealing with the action of the oscillating and non-oscillating audion". The organization's board refused to allow him, and issued

9153-418: The manufacturing process. His first success was in demonstrating that, contrary to what Edison and others had long asserted, incandescent lamps could function more efficiently and with longer life if the glass envelope was filled with low-pressure inert gas rather than a complete vacuum. However, this only worked if the gas used was meticulously 'scrubbed" of all traces of oxygen and water vapor. He then applied

9266-402: The marketing and financial clout of RCA, Armstrong decided to finance his own development and form ties with smaller members of the radio industry, including Zenith and General Electric , to promote his invention. Armstrong thought that FM had the potential to replace AM stations within 5 years, which he promoted as a boost for the radio manufacturing industry, then suffering from the effects of

9379-477: The mid-1920s, Armstrong began researching a solution. He initially, and unsuccessfully, attempted to resolve the problem by modifying the characteristics of AM transmissions. One approach used frequency modulation (FM) transmissions. Instead of varying the strength of the carrier wave as with AM, the frequency of the carrier was changed to represent the audio signal. In 1922 John Renshaw Carson of AT&T, inventor of Single-sideband modulation (SSB), had published

9492-491: The noise produced in receivers, by vacuum tubes. Armstrong had a standing agreement to give RCA the right of first refusal to his patents. In 1934 he presented his new system to RCA president Sarnoff. Sarnoff was somewhat taken aback by its complexity, as he had hoped it would be possible to eliminate static merely by adding a simple device to existing receivers. From May 1934 until October 1935 Armstrong conducted field tests of his FM technology from an RCA laboratory located on

9605-552: The original names. De Forest continued to manufacture and supply Audions to the US Navy up until the early 1920s, for maintenance of existing equipment, but elsewhere they were regarded as well and truly obsolete by then. It was the vacuum triode that made practical radio broadcasts a reality. Prior to the introduction of the Audion, radio receivers had used a variety of detectors including coherers , barretters , and crystal detectors . The most popular crystal detector consisted of

9718-480: The partial vacuum. Much of the research that led to the development of true vacuum tubes was carried out by Irving Langmuir in the General Electric (GE) research laboratories. Langmuir had long suspected that certain assumed limitations on the performance of various low-pressure and vacuum electrical devices, might not be fundamental physical limitations at all, but simply due to contamination and impurities in

9831-474: The public for the original band. Although converters allowing low band FM sets to receive high band were manufactured, they ultimately proved to be complicated to install, and often as (or more) expensive than buying a new high band set outright. Armstrong felt the FM band reassignment had been inspired primarily by a desire to cause a disruption that would limit FM's ability to challenge the existing radio industry, including RCA's AM radio properties that included

9944-445: The regeneration patent became separated into two groups of court cases. An initial court action was triggered in 1919 when Armstrong sued de Forest's company in district court, alleging infringement of patent 1,113,149. This court ruled in Armstrong's favor on May 17, 1921. A second line of court cases, the result of the patent office interference hearing, had a different outcome. The interference board had also sided with Armstrong, but he

10057-507: The regenerative circuit, the superheterodyne, and frequency modulation." The ITU added him to its roster of great inventors of electricity in 1955. He later received two honorary doctorates, from Columbia in 1929, and Muhlenberg College in 1941. In 1980, he was inducted into the National Inventors Hall of Fame , and appeared on a U.S. postage stamp in 1983. The Consumer Electronics Hall of Fame inducted him in 2000, "in recognition of his contributions and pioneering spirit that have laid

10170-704: The rest of his life, Armstrong was afflicted with a physical tic exacerbated by excitement or stress. Due to this illness, he withdrew from public school and was home-tutored for two years. To improve his health, the Armstrong family moved to a house overlooking the Hudson River, at 1032 Warburton Avenue in Yonkers . The Smith family subsequently moved next door. Armstrong's tic and the time missed from school led him to become socially withdrawn. From an early age, Armstrong showed an interest in electrical and mechanical devices, particularly trains. He loved heights and constructed

10283-468: The same approach to producing a rectifier for the newly developed "Coolidge" X-ray tubes. Again contrary to what had been widely believed to be possible, by virtue of meticulous cleanliness and attention to detail, he was able to produce versions of the Fleming Diode that could rectify hundreds of thousands of volts. His rectifiers were called "Kenotrons" from the Greek keno (empty, contains nothing, as in

10396-411: The spirit moves me." Armstrong had arranged to have photographs taken, which he had delivered to David Sarnoff's secretary, Marion McInnis. Armstrong and McInnis married later that year. Armstrong bought a Hispano-Suiza motor car before the wedding, which he kept until his death, and which he drove to Palm Beach, Florida for their honeymoon. A publicity photograph was made of him presenting Marion with

10509-419: The telephone industry for at least two decades. (Ironically, in the years of patent disputes leading up to World War I, it was only this "loophole" that allowed vacuum triodes to be manufactured at all since de Forest's grid Audion patent did not mention this application). De Forest was granted a patent for his early two-electrode diode version of the Audion on November 13, 1906 ( U.S. patent 841,386 ), and

10622-404: The time greatly underestimated the potential of his grid Audion, imagining it to be limited to mostly military applications. It is significant that de Forest apparently did not see its potential as a telephone repeater amplifier at the time he filed the patent claiming it, even though he had previously patented amplification devices and crude electromechanical note magnifiers had been the bane of

10735-426: The time. De Forest's initial Audions did not have a high vacuum and developed a blue glow at modest plate voltages; De Forest improved the vacuum for Federal Telegraph. By 1912, vacuum tube operation was understood, and regenerative circuits using high-vacuum tubes were appreciated. While growing up, Armstrong had experimented with the early temperamental, "gassy" Audions. Spurred by the later discoveries, he developed

10848-472: The tube in the form of a metal hydride , heated with an auxiliary filament; hydrogen by heating such storage element can be used to replenish cleaned-up gas, and even to adjust the pressure as needed for a thyratron operation at a given voltage. Deuterium is used in ultraviolet lamps for ultraviolet spectroscopy , in neutron generator tubes, and in special tubes (e.g. crossatron ). It has higher breakdown voltage than hydrogen. In fast switching tubes it

10961-521: The tube. Although the envelope is typically glass, power tubes often use ceramics , and military tubes often use glass-lined metal. Both hot cathode and cold cathode type devices are encountered. Hydrogen is used in tubes used for very fast switching, e.g. some thyratrons , dekatrons , and krytrons , where very steep edges are required. The build-up and recovery times of hydrogen are much shorter than in other gases. Hydrogen thyratrons are usually hot-cathode. Hydrogen (and deuterium) can be stored in

11074-604: The two papers was reprinted in other journals such as the Annals of the New York Academy of Sciences . When Armstrong and de Forest later faced each other in a dispute over the regeneration patent, Armstrong was able to demonstrate conclusively that de Forest still had no idea how it worked. The problem was that (possibly to distance his invention from the Fleming valve) de Forest's original patents specified that low-pressure gas inside

11187-414: The vacancy left by John H. Morecroft's death, receiving an appointment as a professor of Electrical Engineering at Columbia, a position he held the remainder of his life. Armstrong began working on his first major invention while still an undergraduate at Columbia. In late 1906, Lee de Forest had invented the three-element (triode) "grid Audion" vacuum-tube. How vacuum tubes worked was not understood at

11300-538: The world's first portable superheterodyne radio as a wedding gift. He was an avid tennis player until an injury in 1940, and drank an Old Fashioned with dinner. Politically, he was described by one of his associates as "a revolutionist only in technology – in politics he was one of the most conservative of men." In 1955, Marion Armstrong founded the Armstrong Memorial Research Foundation, and participated in its work until her death in 1979 at

11413-401: Was affected by the presence of radio waves . De Forest found that gas in a partial vacuum heated by a conventional lamp filament behaved much the same way, and that if a wire were wrapped around the glass housing, the device could serve as a detector of radio signals. In his original design, a small metal plate was sealed into the lamp housing, and this was connected to the positive terminal of

11526-511: Was an American electrical engineer and inventor who developed FM ( frequency modulation ) radio and the superheterodyne receiver system. He held 42 patents and received numerous awards, including the first Medal of Honor awarded by the Institute of Radio Engineers (now IEEE ), the French Legion of Honor , the 1941 Franklin Medal and the 1942 Edison Medal . He achieved the rank of major in

11639-487: Was an interference hearing at the patent office to determine priority. De Forest was not the only other inventor involved – the four competing claimants included Armstrong, de Forest, General Electric's Langmuir , and Alexander Meissner , who was a German national, which led to his application being seized by the Office of Alien Property Custodian during World War I. Following the end of WWI Armstrong enlisted representation by

11752-754: Was born in the Chelsea district of New York City, the oldest of John and Emily (née Smith) Armstrong's three children. His father began working at a young age at the American branch of the Oxford University Press , which published bibles and standard classical works, eventually advancing to the position of vice president. His parents first met at the North Presbyterian Church, located at 31st Street and Ninth Avenue. His mother's family had strong ties to Chelsea, and an active role in church functions. When

11865-602: Was challenged, triggering another patent office interference hearing. Armstrong ultimately lost this patent battle; although the outcome was less controversial than that involving the regeneration proceedings. The challenger was Lucien Lévy of France who had worked developing Allied radio communication during WWI. He had been awarded French patents in 1917 and 1918 that covered some of the same basic ideas used in Armstrong's superheterodyne receiver. AT&T, interested in radio development at this time, primarily for point-to-point extensions of its wired telephone exchanges, purchased

11978-434: Was disabled and the transmitter keyed to produce quarter-second CW pulses. The narrow-band (57 Hz) receiver, which tracked the transmitter frequency, got an incremental tuning control to compensate for the possible 300 Hz Doppler shift on the lunar echoes. They achieved success on 10 January 1946. Bitter and overtaxed by years of litigation and mounting financial problems, Armstrong lashed out at his wife one day with

12091-849: Was famous for saying that he "didn't know why it worked, it just did". He always referred to the vacuum triodes developed by other researchers as "Oscillaudions", although there is no evidence that he had any significant input to their development. It is true that after the invention of the true vacuum triode in 1913 (see below), de Forest continued to manufacture various types of radio transmitting and receiving apparatus, (examples of which are illustrated on this page). However, although he routinely described these devices as using "Audions", they actually used high-vacuum triodes, using circuitry very similar to that developed by other experimenters. In 1914, Columbia University student Edwin Howard Armstrong worked with professor John Harold Morecroft to document

12204-587: Was fiercely opposed as unneeded by Armstrong, but he lost. The FCC made its decision final on June 27, 1945. It allocated 100 FM channels from 88 to 108 MHz, and assigned the former FM band to 'non government fixed and mobile' (42–44 MHz), and television channel 1 (44–50 MHz), now sidestepping the interference concerns. A period of allowing existing FM stations to broadcast on both low and high bands ended at midnight on January 8, 1949, at which time any low band transmitters were shut down, making obsolete 395,000 receivers that had already been purchased by

12317-654: Was heartbroken at being unable to see her once again, and expressing deep regret at having hurt her, the dearest thing in his life." The note concluded, "God keep you and Lord have mercy on my Soul." David Sarnoff disclaimed any responsibility, telling Carl Dreher directly that "I did not kill Armstrong." After his death, a friend of Armstrong estimated that 90 percent of his time was spent on litigation against RCA. U.S. Senator Joseph McCarthy (R-Wisconsin) reported that Armstrong had recently met with one of his investigators, and had been "mortally afraid" that secret radar discoveries by him and other scientists "were being fed to

12430-501: Was issued for his discovery. Although Lee de Forest initially discounted Armstrong's findings, beginning in 1915 de Forest filed a series of competing patent applications that largely copied Armstrong's claims, now stating that he had discovered regeneration first, based on a notebook entry made on August 6, 1912, while working for the Federal Telegraph company, prior to the date recognized for Armstrong of January 31, 1913. The result

12543-559: Was preparing apparatus to counteract a claim made by a patent attorney, he "accidentally ran into the phenomenon of super-regeneration", where, by rapidly "quenching" the vacuum-tube oscillations, he was able to achieve even greater levels of amplification. A year later, in 1922, Armstrong sold his super-regeneration patent to RCA for $ 200,000 plus 60,000 shares of corporation stock, which was later increased to 80,000 shares in payment for consulting services. This made Armstrong RCA's largest shareholder, and he noted that "The sale of that invention

12656-639: Was to net me more than the sale of the regenerative circuit and the superheterodyne combined". RCA envisioned selling a line of super-regenerative receivers until superheterodyne sets could be perfected for general sales, but it turned out the circuit was not selective enough to make it practical for broadcast receivers. "Static" interference – extraneous noises caused by sources such as thunderstorms and electrical equipment – bedeviled early radio communication using amplitude modulation and perplexed numerous inventors attempting to eliminate it. Many ideas for static elimination were investigated, with little success. In

12769-471: Was unwilling to settle with de Forest for less than what he considered full compensation. Thus pressured, de Forest continued his legal defense, and appealed the interference board decision to the District of Columbia district court. On May 8, 1924, that court ruled that it was de Forest who should be considered regeneration's inventor. Armstrong (along with much of the engineering community) was shocked by these events, and his side appealed this decision. Although

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