Alexanderson Alternator in the Grimeton VLF transmitter.

An Alexanderson alternator is a rotating machine invented by Ernst Alexanderson for the generation of high frequency alternating current up to 100 kHz, for the purpose of radio communication. It is on the list of IEEE Milestones as a key achievement in electrical engineering. Image File history File linksMetadata Size of this preview: 800 × 600 pixelsFull resolution (2048 × 1536 pixel, file size: 828 KB, MIME type: image/jpeg) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Size of this preview: 800 × 600 pixelsFull resolution (2048 × 1536 pixel, file size: 828 KB, MIME type: image/jpeg) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... VLF transmitter Grimeton The Grimeton VLF transmitter is a VLF transmission facility near Grimeton close to Varberg in Sweden. ... Early 20th century Alternator made in Budapest, Hungary, in the power generating hall of a hydroelectric station. ... Ernst Frederick Werner Alexanderson (January 25, 1878–May 14, 1975) was a Swedish-American electrical engineer. ... City lights viewed in a motion blurred exposure. ... This List of IEEE Milestones contains the Institute of Electrical and Electronics Engineers (IEEE) Milestones, representing key historical achievements in electrical and electronic engineering. ... Electrical Engineers design power systems… … and complex electronic circuits. ...

History

In 1891, Frederick Thomas Trouton gave a lecture which stated that, if an electrical alternator were run at a great enough speed, it would generate wireless energy [1]. Nikola Tesla's U.S. Patent 447,920 , "Method of Operating Arc-Lamps" (March 10, 1891), described an alternator that produces high-frequency current for that time period, around 10,000 cycles per second (later to be known as Hertz). A forerunner to the Alexanderson alternator, it produced frequencies which were in the longwave radio frequency range (VLF band). Tesla continued research into higher frequency alternators and, by early 1896, he attained the means to produce CW (or "continuous wave") waves around 50,000 cycles per second for radio transmission. ^[1] Year 1891 (MDCCCXCI) was a common year starting on Thursday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Saturday of the 12-day slower Julian calendar). ... Frederick Thomas Trouton (November 24, 1863, Dublin – September 21, 1922, Downe) was a physicist best known for what became known as Troutons Law, namely L/T, the change of entropy per mole in evaporation at the boiling point, is constant. ... This article or section is in need of attention from an expert on the subject. ... The hertz (symbol: Hz) is the SI unit of frequency. ... This article does not cite any references or sources. ... Very low frequency or VLF refers to radio frequencies (RF) in the range of 3 to 30 kHz. ... A continuous wave (CW) is an electromagnetic wave of constant amplitude and frequency. ... Low Frequency or LF refers to Radio Frequencies (RF) in the range of 30–300 kHz. ... In communications, transmission is the act of transmitting electrical messages (and the associated phenonomena of radiant energy that pass through media). ...

In 1904, Reginald Fessenden contracted with General Electric for an alternator that generated a frequency of 100,000 cycles per second for "continuous" radio. E. F. W. Alexanderson designed the Alexanderson alternator, which produced such alternating currents at General Electric. The Alexanderson alternator was extensively used for long wave radio communications by shore stations, but was too large and heavy to be installed on most ships. Alexanderson would later receive U.S. Patent 1,008,577  in 1911 for his device. The Alexanderson alternator followed Fessenden's rotary spark-gap transmitter as the second radio transmitter to be modulated to carry the sound of the human voice. Until the invention of vacuum tube (thermionic valve) oscillators in the 1920's, the Alexanderson alternator was an important high-power radio transmitter, and allowed amplitude modulation radio transmission of the human voice. The last remaining workable Alexanderson alternator is at the VLF transmitter Grimeton in Sweden. 1904 (MCMIV) was a leap year starting on a Friday (see link for calendar). ... Reginald Aubrey Fessenden (October 6, 1866 – July 22, 1932) was a Canadian-born inventor, best known for his work in early radio. ... GE redirects here. ... A continuous wave (CW) is an electromagnetic wave of constant amplitude and frequency. ... Longwave radio frequencies are those below 500 kHz, which correspond to wavelengths longer than 600 meters. ... Year 1911 (MCMXI) was a common year starting on Sunday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Saturday of the 13-day-slower Julian calendar). ... Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ... Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ... Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ... Cross coupled LC oscillator with output on top An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave. ... 1920 (MCMXX) was a leap year starting on Thursday. ... Antenna tower of Crystal Palace transmitter, London A transmitter (sometimes abbreviated XMTR) is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. ... Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ... VLF transmitter Grimeton The VLF transmitter Grimeton is a VLF transmission facility near Grimeton close to Varberg in Sweden. ...

Stations

starting in 1942 four stations were operated by US Navy: the re-established station Haiku (Hawaii) as well as stations in Bolinas (both until 1946), Marion and Tuckerton (both until 1948). The Marion station was transferred in 1949 to the US Air Caernarfon (the original Welsh spelling is now almost always used in preference to the anglicised forms, Caernarvon or Carnarvon) is a royal town in north-west Wales. ... Motto: Contemnit procellas (It defies the storms) Semper invicta (Always invincible) Coordinates: Country Poland Voivodeship Masovia Powiat city county Gmina Warszawa Districts 18 boroughs City Rights turn of the 13th century Government  - Mayor Hanna Gronkiewicz-Waltz (PO) Area  - City 516. ... Nickname: Motto: Ut luceat omnibus Latin: That it may shine on all (Matthew 5:15) Location in Brazil Founded March 12, 1537 Incorporated (as village) 1709 Incorporated (as city) 1823 Government  - Mayor João Paulo Lima e Silva (PT) Area  - City 218 km²  (84. ...

Force and used until 1957 for the transmission of weather forecasts to the arctic as well as for the Basen to Greenland, Labrador and Iceland. One the Alternators was scrapped 1961 and the other one was handed over to US the office OF standard. The two machines in Brazil were never used because of organizational problems there. They were returned to Radio Central after 1946.

Theory of operation

The Alexanderson alternator operates by variable reluctance (similar to an electric guitar pickup), changing the magnetic flux linking two coils. The alternator has a circular laminated iron stator carrying two sets of coils, in a C-shape. One set of coils is energized with direct current and produces a magnetic field in the air gap of the stator. The second set of coils generates the radio-frequency voltage. The rotor is a laminated iron disk with holes or slots cut into its circumferance. The openings are filled with non-magnetic material so as to reduce air drag. The rotor has no windings or electrical connections. Magnetic reluctance is the resistance of a material to a magnetic field. ... A pickup device acts as a detector and captures mechanical vibrations (usually from suitably equipped stringed instruments such as the electric guitar, electric bass guitar and violin) and converts them to an electronic signal which can be amplified and recorded. ... This template is misplaced. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... It has been suggested that this article or section be merged with Radio waves. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ...

As the rotor turns, either an iron portion of the disk is in the gap of the stator, allowing a high magnetic flux to cross the gap, or else a non-magnetic slot is in the stator gap, allowing less magnetic flux to pass. These changes in flux induce a voltage in a second set of coils on the stator.

The RF collector coils were all interconnected by an output transformer, whose secondary winding was connected to the antenna circuit. Modulation or telegraph keying of the radio frequency energy was done by a magnetic amplifier, which was also used for amplitude modulation and voice transmissions. Three-phase pole-mounted step-down transformer. ... In telecommunications, modulation is the process of varying a periodic waveform, i. ... Optical Telegraf of Claude Chappe on the Litermont near Nalbach, Germany Telegraphy (from the Greek words tele (τηλε) = far and graphein (γραφειν) = write) is the long-distance transmission of written messages without physical transport of letters, originally by changing something that could be observed from a distance (optical telegraphy). ... The magnetic amplifier is an electromagnetic device for amplifying electrical signals. ... Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ...

The radio frequency emitted by an Alexanderson alternator in Hertz is simply the product of the number of stator pole pairs and the revolutions per second. Higher radio frequencies thus require more pole pairs, a higher rotational speed, or both.

Performance advantages

A large Alexanderson alternator might produce 200 kW of output radio-frequency energy and would be water- or oil-cooled. One such machine had 600 pole pairs in the stator winding and the rotor was driven at 2170 RPM, for an output frequency near 21.7 kHz. To obtain higher frequencies, higher rotor speeds were required, up to 20,000 RPM.

Unlike the spark-gap transmitters and arc converters also used at the time, the Alexanderson alternator produced a continuous wave output of higher purity. With a spark transmitter, the electromagnetic energy is spread over very wide sidebands, effectively transmitting on several frequencies at once. With a continuous-wave transmitter such as the Alexanderson Alternator (or the Poulsen Arc type), the energy is concentrated onto a single frequency, greatly improving the transmission efficiency. A typical spark transmitter circuit. ... // The arc converter, sometimes called the arc transmitter or Poulsen arc after its inventor Valdemar Poulsen, is a device used to convert DC energy into RF energy. ... A continuous wave (CW) is an electromagnetic wave of constant amplitude and frequency. ...

The frequency of the transmitted signal was directly related to the rotor speed, so an automatic speed regulator was always employed to maintain a stable transmit frequency; the speed regulator was designed to compensate for the effect of keying (and the subsequently varying load) upon the rotor speed.

Disadvantages

Because of the extremely high rotational speed compared to a conventional alternator, the Alexanderson alternator required continuous maintenance by highly skilled personnel. Efficient lubrication and oil or water cooling was essential for reliability, difficult to achieve with the lubricants available at the time. In fact early editions of the British Navy's "Admiralty Handbook of Wireless Telegraphy" cover this in considerable detail, mostly as an explanation as to why "The Navy" did not use that particular technology. The technology was however, widely used by the U.S. Navy.

Other major problems were that changing the operating frequency was a lengthy and complicated process, and that, unlike a spark transmitter, the carrier signal could not be switched on and off at will. The latter problem greatly complicated "listening through" (that is, stopping the transmission to listen for any answer). There was also the risk that it would allow enemy vessels to detect the presence of the ship.

Finally, because it would require both a large number of stators and an extremely high rotational frequency, the Alexanderson alternator is at most capable of transmission in the lower mediumwave band, with shortwave and microwave being physically impossible.

See also

• Alexanderson Day

The Alexanderson Day (named after the inventor Ernst Fredrik Werner Alexanderson) is the great day of the open oor at the VLF transmitter Grimeton. ...

Notes

1. ^ Leland Anderson, "Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony, and Transmission of Power", Sun Publishing Company, LC 92-60482, ISBN 0-9632652-0-2

References

• Antique Wireless Association - column edited by Frank Lotito
• David E. Fisher and Marshall J. Fisher, Tube, the Invention of Television Counterpoint, Washington D.C. USA, (1996) ISBN 1-887178-17-1
• IEEE History Center

Patents

• E. F. W. Alexanderson, U.S. Patent 1,008,577 
• N. Tesla , U.S. Patent 447,921 

External link

• Description of the 200 kW alternator at New Brunswick