1.
Grimeton VLF transmitter
–
The Varberg Radio Station at Grimeton is a VLF transmission facility at Grimeton close to Varberg, in Halland, Sweden. It has the only working Alexanderson alternator rotating armature radio transmitter in the world and is classified as a World Heritage Site and it is an anchor site for the European Route of Industrial Heritage. The transmitter was built in 1922 to 1924, to operate at 17.2 kHz, the Grimeton VLF transmitter location is also used for shortwave transmissions, FM and TV broadcasting. For this purpose, a 260 metre high guyed steel framework mast was built in 1966 next to the containing the 40 kHz transmitter. Until the 1950s, the Grimeton VLF transmitter was used for radio telegraphy to Radio Central in Long Island, New York. From the 1960s until 1996 it transmitted orders to submarines in the Swedish Navy, in 1968 a second transmitter was installed which uses the same aerial as the machine transmitter but with transistor and tube technology. The Alexanderson transmitter became obsolete in 1996 and went out of service, however, because it was still in good condition it was declared a national monument and can be visited during the summer. On July 2,2004, the Grimeton VLF transmitter was declared a World Cultural Heritage site by UNESCO and it continues to be used on special occasions such as Alexanderson Day to transmit Morse messages on 17.2 kHz. The Grimeton/Varberg site is used by the Swedish Navy, transmitting on 40.4 kHz using call sign SRC using the vacuum tube transmitter. Therefore the special transmissions from that machine transmitter are very rare, recent transmissions from SAQ on 17.2 kHz took place on December 24,2013, June 29,2014, December 24,2014, June 28,2015 and July 3,2016. At least two regular transmissions take place each year, on the first Sunday of July and on Christmas Eve, plus one or two extra transmissions on special occasions or for testing
Grimeton VLF transmitter
–
UNESCO World Heritage Site
Grimeton VLF transmitter
–
Alexanderson alternator in the Grimeton VLF transmitter. The drive motor is at the extreme right; the speed-increaser gearbox is just to its left. Note the bronze-colored shaft coupling.
2.
Alternator
–
An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a magnetic field with a stationary armature. Occasionally, an alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, an alternator that uses a permanent magnet for its magnetic field is called a magneto. Alternators in power stations driven by steam turbines are called turbo-alternators, large 50 or 60 Hz three phase alternators in power plants generate most of the worlds electric power, which is distributed by electric power grids. Alternating current generating systems were known in simple forms from the discovery of the induction of electric current in the 1830s. Rotating generators naturally produced alternating current but, since there was use for it, it was normally converted into direct current via the addition of a commutator in the generator. The early machines were developed by such as Michael Faraday. Faraday developed the rotating rectangle, whose operation was heteropolar – each active conductor passed successively through regions where the field was in opposite directions. Lord Kelvin and Sebastian Ferranti also developed early alternators, producing frequencies between 100 and 300 Hz, supplying the proper amount of voltage from generating stations in these early systems was left up to the engineers skill in riding the load. In 1883 the Ganz Works invented the constant voltage generator that could produce an output voltage. The introduction of transformers in the led to the widespread use of alternating current. After 1891, polyphase alternators were introduced to supply currents of multiple differing phases, later alternators were designed for various alternating current frequencies between sixteen and about one hundred hertz, for use with arc lighting, incandescent lighting and electric motors. A conductor moving relative to a magnetic field develops an electromotive force in it and this emf reverses its polarity when it moves under magnetic poles of opposite polarity. Typically, a magnet, called the rotor turns within a stationary set of conductors wound in coils on an iron core. The field cuts across the conductors, generating an induced EMF, the rotating magnetic field induces an AC voltage in the stator windings. Since the currents in the stator windings vary in step with the position of the rotor, the rotors magnetic field may be produced by permanent magnets, or by a field coil electromagnet. Automotive alternators use a rotor winding which allows control of the generated voltage by varying the current in the rotor field winding
Alternator
–
Early 20th-century alternator made by
Ganz Works in
1909 in
Budapest,
Hungary, in the power generating hall of the biggest
hydroelectric station of the
Russian Empire (photograph by
Prokudin-Gorsky, 1911)
Alternator
–
Alternator mounted on an automobile engine with a
serpentine belt pulley
3.
Alternating current
–
Alternating current, is an electric current which periodically reverses direction, whereas direct current flows only in one direction. A common source of DC power is a cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, the usual waveform of alternating current in most electric power circuits is a sine wave. In certain applications, different waveforms are used, such as triangular or square waves, audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information encoded onto the AC signal and these currents typically alternate at higher frequencies than those used in power transmission. Electrical energy is distributed as alternating current because AC voltage may be increased or decreased with a transformer, use of a higher voltage leads to significantly more efficient transmission of power. The power losses in a conductor are a product of the square of the current and this means that when transmitting a fixed power on a given wire, if the current is halved, the power loss will be four times less. Power is often transmitted at hundreds of kilovolts, and transformed to 100–240 volts for domestic use, high voltages have disadvantages, such as the increased insulation required, and generally increased difficulty in their safe handling. In a power plant, energy is generated at a convenient voltage for the design of a generator, near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer voltages vary somewhat depending on the country and size of load, the voltage delivered to equipment such as lighting and motor loads is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world, high-voltage direct-current electric power transmission systems have become more viable as technology has provided efficient means of changing the voltage of DC power. HVDC systems, however, tend to be expensive and less efficient over shorter distances than transformers. Three-phase electrical generation is very common, the simplest way is to use three separate coils in the generator stator, physically offset by an angle of 120° to each other. Three current waveforms are produced that are equal in magnitude and 120° out of phase to each other, if coils are added opposite to these, they generate the same phases with reverse polarity and so can be simply wired together. In practice, higher pole orders are commonly used, for example, a 12-pole machine would have 36 coils. The advantage is that lower rotational speeds can be used to generate the same frequency, for example, a 2-pole machine running at 3600 rpm and a 12-pole machine running at 600 rpm produce the same frequency, the lower speed is preferable for larger machines. If the load on a system is balanced equally among the phases. Even in the worst-case unbalanced load, the current will not exceed the highest of the phase currents
Alternating current
–
High voltage transmission lines deliver power from
electric generation plants over long distances using alternating current. These particular lines are located in eastern
Utah.
Alternating current
–
Alternating current (green curve). The horizontal axis measures time; the vertical, current or voltage.
Alternating current
–
The prototype of ZBD. transformer is on display at the Széchenyi István Memorial Exhibition,
Nagycenk,
Hungary
Alternating current
4.
Transmitter
–
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which generates a radio frequency alternating current. When a connected antenna is excited by this current, the antenna emits radio waves. The term transmitter is usually limited to equipment that generates radio waves for communication purposes, or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as ovens or diathermy equipment, are not usually called transmitters even though they often have similar circuits. The term is used more specifically to refer to a broadcast transmitter. This usage typically includes both the proper, the antenna, and often the building it is housed in. A transmitter can be a piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver, the term transmitter is often abbreviated XMTR or TX in technical documents. The purpose of most transmitters is radio communication of information over a distance, the transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, which is called the carrier signal. The information can be added to the carrier in several different ways, in an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude. In a frequency modulation transmitter, it is added by varying the signals frequency slightly. Many other types of modulation are used, the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as phones, walkie-talkies. In more powerful transmitters, the antenna may be located on top of a building or on a tower, and connected to the transmitter by a feed line. The first primitive radio transmitters were built by German physicist Heinrich Hertz in 1887 during his investigations of radio waves. These generated radio waves by a high voltage spark between two conductors, beginning in 1895 Guglielmo Marconi developed the first practical radio communication systems using spark transmitters. These spark-gap transmitters were used during the first three decades of radio, called the wireless telegraphy or spark era, vacuum tube transmitters took over because they were inexpensive and produced continuous waves, which could be modulated to transmit audio using amplitude modulation. This made possible commercial AM radio broadcasting, which began in about 1920, experimental television transmission had been conducted by radio stations since the late 1920s, but practical television broadcasting didnt begin until the 1940s
Transmitter
–
Continental 816R-5B 35 kW FM transmitter, belonging to American FM radio station KWNR broadcasting on 95.5 MHz in Las Vegas
Transmitter
–
Commercial
FM broadcasting transmitter at radio station
WDET-FM, Wayne State University, Detroit, USA. It broadcasts at 101.9
MHz with a radiated power of 48
kW.
Transmitter
–
Modern
amateur radio transceiver, the ICOM IC-746PRO. It can transmit on the amateur bands from 1.8 MHz to 144 MHz with an output power of 100 W
Transmitter
–
A
CB radio transceiver, a
two way radio transmitting on 27 MHz with a power of 4 W, that can be operated without a license
5.
Continuous wave
–
A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency, a sine wave. In mathematical analysis, it is considered to be of infinite duration, continuous wave is also the name given to an early method of radio transmission, in which a sinusoidal carrier wave is switched on and off. Information is carried in the duration of the on and off periods of the signal. Very early radio transmitters used a gap to produce radio-frequency oscillations in the transmitting antenna. The signals produced by these spark-gap transmitters consisted of strings of brief pulses of radio frequency oscillations which died out rapidly to zero. The disadvantage of damped waves was that their energy was spread over a wide band of frequencies. As a result they produced electromagnetic interference that spread over the transmissions of stations at other frequencies and this motivated efforts to produce radio frequency oscillations that decayed more slowly, had less damping. Manufacturers produced spark transmitters which generated long ringing waves with minimal damping and it was realized that the ideal radio wave for radiotelegraphic communication would be a sine wave with zero damping, a continuous wave. An unbroken continuous sine wave theoretically has no bandwidth, all its energy is concentrated at a single frequency, continuous waves could not be produced with an electric spark, but were achieved with the vacuum tube electronic oscillator, invented around 1913 by Edwin Armstrong and Alexander Meissner. Damped wave spark transmitters were replaced by continuous wave vacuum tube transmitters around 1920, what is transmitted in the extra bandwidth used by a transmitter that turns on/off more abruptly is known as key clicks. Certain types of power used in transmission may increase the effect of key clicks. The first transmitters capable of producing continuous wave, the Alexanderson alternator and vacuum tube oscillators, early radio transmitters could not be modulated to transmit speech, and so CW radio telegraphy was the only form of communication available. Continuous-wave radio was called radiotelegraphy because like the telegraph, it worked by means of a switch to transmit Morse code. However, instead of controlling the electricity in a cross-country wire and this mode is still in common use by amateur radio operators. In military communications and amateur radio, the terms CW and Morse code are used interchangeably. Morse code may be sent using direct current in wires, sound, or light, a carrier wave is keyed on and off to represent the dots and dashes of the code elements. The carriers amplitude and frequency remains constant during each code element, at the receiver, the received signal is mixed with a heterodyne signal from a BFO to change the radio frequency impulses to sound. Though most commercial traffic has now ceased operation using Morse it is popular with amateur radio operators
Continuous wave
–
A commercially manufactured paddle for use with electronic keyer to generate Morse code
6.
Amplitude modulation
–
Amplitude modulation is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In amplitude modulation, the amplitude of the wave is varied in proportion to the waveform being transmitted. That waveform may, for instance, correspond to the sounds to be reproduced by a loudspeaker and this technique contrasts with frequency modulation, in which the frequency of the carrier signal is varied, and phase modulation, in which its phase is varied. AM was the earliest modulation method used to transmit voice by radio and it was developed during the first two decades of the 20th century beginning with Roberto Landell De Moura and Reginald Fessendens radiotelephone experiments in 1900. It remains in use today in many forms of communication, for example it is used in two way radios, VHF aircraft radio, Citizens Band Radio, and in computer modems. AM is often used to refer to mediumwave AM radio broadcasting, when it reaches its destination, the information signal is extracted from the modulated carrier by demodulation. In amplitude modulation, the amplitude or strength of the oscillations is what is varied. For example, in AM radio communication, a continuous wave signal has its amplitude modulated by an audio waveform before transmission. The audio waveform modifies the amplitude of the wave and determines the envelope of the waveform. In the frequency domain, amplitude modulation produces a signal with power concentrated at the carrier frequency, each sideband is equal in bandwidth to that of the modulating signal, and is a mirror image of the other. Standard AM is thus sometimes called double-sideband amplitude modulation to distinguish it more sophisticated modulation methods also based on AM. One disadvantage of all amplitude modulation techniques is that the receiver amplifies and detects noise, increasing the received signal to noise ratio, say, by a factor of 10, thus would require increasing the transmitter power by a factor of 10. For this reason AM broadcast is not favored for music and high fidelity broadcasting, another disadvantage of AM is that it is inefficient in power usage, at least two-thirds of the power is concentrated in the carrier signal. The carrier signal contains none of the information being transmitted. However its presence provides a means of demodulation using envelope detection, providing a frequency. The receiver may regenerate a copy of the frequency from a greatly reduced pilot carrier to use in the demodulation process. Even with the carrier totally eliminated in double-sideband suppressed-carrier transmission, carrier regeneration is possible using a Costas phase-locked loop and this doesnt work however for single-sideband suppressed-carrier transmission, leading to the characteristic Donald Duck sound from such receivers when slightly detuned. Single sideband is used widely in amateur radio and other voice communications both due to its power efficiency and bandwidth efficiency
Amplitude modulation
–
One of the crude pre-vacuum tube AM transmitters, a Telefunken
arc transmitter from 1906. The carrier wave is generated by 6 electric arcs in the vertical tubes, connected to a
tuned circuit. Modulation is done by the large carbon microphone (cone shape) in the antenna lead.
Amplitude modulation
–
Fig 1: An audio signal (top) may be carried by a carrier frequency using AM or FM methods.
Amplitude modulation
–
One of the first
vacuum tube AM radio transmitters, built by Meissner in 1913 with an early triode tube by Robert von Lieben. He used it in a historic 36 km (24 mi) voice transmission from Berlin to Nauen, Germany. Compare its small size with above transmitter.
Amplitude modulation
–
Fig 3: The
spectrogram of an AM voice broadcast shows the two sidebands (green) on either side of the carrier (red) with time proceeding in the vertical direction.
7.
Longwave
–
In radio, longwave, also written as long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with relatively long wavelengths. The term is an one, dating from the early 20th century, when the radio spectrum was considered to consist of long, medium. Most modern radio systems and devices use wavelengths which would then have been considered ultra-short, in contemporary usage, the term longwave is not defined precisely, and its meaning varies across the world. Sometimes, part of the frequency band is included. The International Telecommunication Union Region 1 longwave broadcast band falls wholly within the low band of the radio spectrum. Broader definitions of longwave may extend below and/or above it, in the US, the Longwave Club of America is interested in frequencies below the AM broadcast band, i. e. all frequencies below 535 kHz. Because of their wavelength, radio waves in this frequency range can diffract over obstacles like mountain ranges and travel beyond the horizon. This mode of propagation, called ground wave, is the mode in the longwave band. The attenuation of signal strength with distance by absorption in the ground is lower than at higher frequencies, Low frequency ground waves can be received up to 2,000 kilometres from the transmitting antenna. Low frequency waves can also travel long distances by reflecting from the ionosphere, although this method. Reflection occurs at the ionospheric E layer or F layers, skywave signals can be detected at distances exceeding 300 kilometres from the transmitting antenna. Non-directional beacons transmit continuously for the benefit of radio direction finders in marine and they identify themselves by a callsign in Morse code. They can occupy any frequency in the range 190–1750 kHz, in North America, they occupy 190–535 kHz. In ITU Region 1 the lower limit is 280 kHz, there are government broadcast stations in the range 40–80 kHz that transmit coded time signals to radio clocks. Radio controlled clocks receive their time calibration signals with built-in long-wave receivers, long-waves travel by groundwaves that hug the surface of the earth, unlike medium-waves and short-waves. Those higher-frequency signals do not follow the surface of the Earth beyond a few kilometers and these different propagation paths can make the time lag different for every signal received. The military of the United Kingdom, Russian Federation, United States, Germany, in North America during the 1970s, the frequencies 167,179 and 191 kHz were assigned to the short-lived Public Emergency Radio of the United States. Nowadays, in the United States, Part 15 of FCC regulations allow unlicensed use of 136 kHz and this is called Low Frequency Experimental Radio
Longwave
–
The tuning dial on a 1940s radio, showing longwave wavelengths between 800 and 2000 metres, corresponding to frequencies between 375 and 150 kHz
8.
Radiotelegraphy
–
Wireless telegraphy is the transmission of electric telegraphy signals without wires. Wireless telegraphy came to mean Morse code transmitted by radio waves, initially called Hertzian waves, the primitive spark radio transmitters used until World War 1 could not transmit audio. The code sounded like musical beeps in the earphone of the receiver, the receiving radio operator would translate the beeps back into text. The first practical wireless telegraphy transmitters and receivers were developed by Guglielmo Marconi beginning in 1895, by 1910 communication by Hertzian waves was universally referred to as radio, and the term wireless telegraphy has been largely replaced by the more modern term radiotelegraphy. The transmission of sound began to displace wireless telegraphy by the 1920s for many applications, continuous wave radiotelegraphy is regulated by the International Telecommunication Union as emission type A1A. Today, due to modern text transmission methods, Morse code radiotelegraphy for commercial use has become obsolete. On shipboard the computer and satellite linked GMDSS system has largely replaced Morse as a means of communication, Telegraphy is taught on a very limited basis by the military. A CW coastal station, KSM, still exists in California, run primarily as a museum by volunteers, Radio beacons, particularly in the aviation service, but also as placeholders for commercial ship-to-shore systems, also transmit Morse but at very slow speeds. The US Federal Communications Commission does still issue a lifetime commercial Radiotelegraph Operator License and this requires passing a simple written test on regulations, a more complex written exam on technology, and demonstrating Morse reception at 20 words per minute plain language and 16 wpm code groups. Wireless telegraphy is still used today by amateur radio hobbyists where it is commonly referred to as radio telegraphy, continuous wave. However its knowledge is not required to obtain any class of amateur license, a number of wireless electrical signaling schemes including electric currents through water and the ground were investigated for telegraphy before practical radio systems became available. The original telegraph used two wires between two stations to form an electrical circuit or loop. This led to speculation that it might be possible to both wires and therefore transmit telegraph signals through the ground without any wires connecting the stations. Other attempts were made to send the current through bodies of water, in order to span rivers. The first wireless voice telecommunication device, invented in 1880, was the photophone, both electrostatic and electromagnetic induction were used to develop wireless telegraph systems that saw limited commercial application. This system was successful technically but not economically, as there turned out to be little interest by train travelers in a telegraph service. During the Great Blizzard of 1888, this system was used to send, the disabled trains were able to maintain communications via their Edison induction wireless telegraph systems, perhaps the first successful use of wireless telegraphy to send distress calls. The most successful creator of an electromagnetic induction telegraph system was William Preece in the United Kingdom, beginning with tests across the Bristol Channel in 1892, Preece was able to telegraph across gaps of about 5 kilometres
Radiotelegraphy
–
A radio operator receiving a wireless telegraphy message using a radio wave based Marconi magnetic detector c.1903
Radiotelegraphy
–
Marconi Monument on the
Isle of Wight, England
Radiotelegraphy
–
Muirhead Morse inker. Apparatus similar to that used by Marconi in 1897
Radiotelegraphy
–
Post Office Engineers inspect
Marconi 's equipment on Flat Holm, May 1897
9.
Morse code
–
Morse code is a method of transmitting text information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment. It is named for Samuel F. B, Morse, an inventor of the telegraph. Because many non-English natural languages use more than the 26 Roman letters, each Morse code symbol represents either a text character or a prosign and is represented by a unique sequence of dots and dashes. The duration of a dash is three times the duration of a dot, each dot or dash is followed by a short silence, equal to the dot duration. The letters of a word are separated by an equal to three dots, and the words are separated by a space equal to seven dots. The dot duration is the unit of time measurement in code transmission. To increase the speed of the communication, the code was designed so that the length of each character in Morse varies approximately inversely to its frequency of occurrence in English. Thus the most common letter in English, the letter E, has the shortest code, Morse code is used by some amateur radio operators, although knowledge of and proficiency with it is no longer required for licensing in most countries. Pilots and air controllers usually need only a cursory understanding. Aeronautical navigational aids, such as VORs and NDBs, constantly identify in Morse code, compared to voice, Morse code is less sensitive to poor signal conditions, yet still comprehensible to humans without a decoding device. Morse is, therefore, an alternative to synthesized speech for sending automated data to skilled listeners on voice channels. Many amateur radio repeaters, for example, identify with Morse, in an emergency, Morse code can be sent by improvised methods that can be easily keyed on and off, making it one of the simplest and most versatile methods of telecommunication. The most common signal is SOS or three dots, three dashes, and three dots, internationally recognized by treaty. Beginning in 1836, the American artist Samuel F. B, Morse, the American physicist Joseph Henry, and Alfred Vail developed an electrical telegraph system. This system sent pulses of current along wires which controlled an electromagnet that was located at the receiving end of the telegraph system. A code was needed to transmit natural language using only these pulses, around 1837, Morse, therefore, developed an early forerunner to the modern International Morse code. Around the same time, Carl Friedrich Gauss and Wilhelm Eduard Weber as well as Carl August von Steinheil had already used codes with varying lengths for their telegraphs. In 1837, William Cooke and Charles Wheatstone in England began using a telegraph that also used electromagnets in its receivers
Morse code
–
A typical "straight key." This U.S. model, known as the J-38, was manufactured in huge quantities during
World War II, and remains in widespread use today. In a straight key, the signal is "on" when the knob is pressed, and "off" when it is released. Length and timing of the dots and dashes are entirely controlled by the
telegraphist.
Morse code
–
Chart of the Morse code letters and numerals.
Morse code
–
A commercially manufactured iambic paddle used in conjunction with an electronic keyer to generate high-speed Morse code, the timing of which is controlled by the electronic keyer. Manipulation of dual-lever paddles is similar to the
Vibroplex, but pressing the right paddle generates a series of dahs, and squeezing the paddles produces dit-dah-dit-dah sequence. The actions are reversed for left-handed operators.
Morse code
10.
Vacuum tube
–
In electronics, a vacuum tube, an electron tube, or just a tube, or valve, is a device that controls electric current between electrodes in an evacuated container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by the filament and this type is called a thermionic tube or thermionic valve. A phototube, however, achieves electron emission through the photoelectric effect, the simplest vacuum tube, the diode, contains only a heater, a heated electron-emitting cathode, and a plate. Current can only flow in one direction through the device between the two electrodes, as electrons emitted by the travel through the tube and are collected by the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids, Tubes with grids can be used for many purposes, including amplification, rectification, switching, oscillation, and display. In the 1940s the invention of devices made it possible to produce solid-state devices, which are smaller, more efficient, more reliable, more durable. Hence, from the mid-1950s solid-state devices such as transistors gradually replaced tubes, the cathode-ray tube remained the basis for televisions and video monitors until superseded in the 21st century. However, there are still a few applications for which tubes are preferred to semiconductors, for example, the used in microwave ovens. One classification of vacuum tubes is by the number of active electrodes, a device with two active elements is a diode, usually used for rectification. Devices with three elements are used for amplification and switching. Additional electrodes create tetrodes, pentodes, and so forth, which have additional functions made possible by the additional controllable electrodes. X-ray tubes are vacuum tubes. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission, since these sorts of vacuum tubes have functions other than electronic amplification and rectification they are described in their own articles. A vacuum tube consists of two or more electrodes in a vacuum inside an airtight enclosure, most tubes have glass envelopes, though ceramic and metal envelopes have been used. The electrodes are attached to leads which pass through the envelope via an airtight seal, Tubes were a frequent cause of failure in electronic equipment, and consumers were expected to be able to replace tubes themselves. In addition to the terminals, some tubes had an electrode terminating at a top cap. The principal reason for doing this was to avoid leakage resistance through the tube base, the bases were commonly made with phenolic insulation which performs poorly as an insulator in humid conditions. There was even a design that had two top cap connections
Vacuum tube
–
Modern vacuum tubes, mostly miniature style
Vacuum tube
–
One of Edison's experimental bulbs
Vacuum tube
–
Fleming's first diodes
Vacuum tube
–
The first triode, the De Forest
Audion, invented in 1906
11.
Electrical engineering
–
Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics, and electromagnetism. This field first became an occupation in the later half of the 19th century after commercialization of the electric telegraph, the telephone. Subsequently, broadcasting and recording media made electronics part of daily life, the invention of the transistor, and later the integrated circuit, brought down the cost of electronics to the point they can be used in almost any household object. Electrical engineers typically hold a degree in engineering or electronic engineering. Practicing engineers may have professional certification and be members of a professional body, such bodies include the Institute of Electrical and Electronics Engineers and the Institution of Engineering and Technology. Electrical engineers work in a wide range of industries and the skills required are likewise variable. These range from basic circuit theory to the management skills required of a project manager, the tools and equipment that an individual engineer may need are similarly variable, ranging from a simple voltmeter to a top end analyzer to sophisticated design and manufacturing software. Electricity has been a subject of scientific interest since at least the early 17th century and he also designed the versorium, a device that detected the presence of statically charged objects. In the 19th century, research into the subject started to intensify, Electrical engineering became a profession in the later 19th century. Practitioners had created an electric telegraph network and the first professional electrical engineering institutions were founded in the UK. Over 50 years later, he joined the new Society of Telegraph Engineers where he was regarded by other members as the first of their cohort, Practical applications and advances in such fields created an increasing need for standardised units of measure. They led to the standardization of the units volt, ampere, coulomb, ohm, farad. This was achieved at a conference in Chicago in 1893. During these years, the study of electricity was considered to be a subfield of physics. Thats because early electrical technology was electromechanical in nature, the Technische Universität Darmstadt founded the worlds first department of electrical engineering in 1882. The first course in engineering was taught in 1883 in Cornell’s Sibley College of Mechanical Engineering. It was not until about 1885 that Cornell President Andrew Dickson White established the first Department of Electrical Engineering in the United States, in the same year, University College London founded the first chair of electrical engineering in Great Britain. Professor Mendell P. Weinbach at University of Missouri soon followed suit by establishing the engineering department in 1886
Electrical engineering
–
Electrical engineers design complex power systems...
Electrical engineering
–
... and electronic circuits.
Electrical engineering
–
The discoveries of
Michael Faraday formed the foundation of electric motor technology
Electrical engineering
–
Thomas Edison, electric light and (DC) power supply networks
12.
Radio wave
–
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 GHz to as low as 3 kHz, though some definitions describe waves above 1 or 3 GHz as microwaves, at 300 GHz, the corresponding wavelength is 1 mm, and at 3 kHz is 100 km. Like all other electromagnetic waves, they travel at the speed of light, naturally occurring radio waves are generated by lightning, or by astronomical objects. Radio waves are generated by radio transmitters and received by radio receivers, the radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses. Radio waves were first predicted by mathematical work done in 1867 by Scottish mathematical physicist James Clerk Maxwell, Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations. Radio waves were first used for communication in the mid 1890s by Guglielmo Marconi, different frequencies experience different combinations of these phenomena in the Earths atmosphere, making certain radio bands more useful for specific purposes than others. It does not necessarily require a cleared sight path, at lower frequencies radio waves can pass through buildings, foliage and this is the only method of propagation possible at microwave frequencies and above. On the surface of the Earth, line of propagation is limited by the visual horizon to about 40 miles. This is the used by cell phones, cordless phones, walkie-talkies, wireless networks, FM and television broadcasting. Indirect propagation, Radio waves can reach points beyond the line-of-sight by diffraction, diffraction allows a radio wave to bend around obstructions such as a building edge, a vehicle, or a turn in a hall. Radio waves also reflect from surfaces such as walls, floors, ceilings, vehicles and these effects are used in short range radio communication systems. Ground waves allow mediumwave and longwave broadcasting stations to have coverage areas beyond the horizon, the nonzero resistance of the earth absorbs energy from ground waves, so as they propagate the waves lose power and the wavefronts bend over at an angle to the surface. As frequency decreases, the decrease and the achievable range increases. Military very low frequency and extremely low frequency communication systems can communicate over most of the Earth, and with submarines hundreds of feet underwater. Tropospheric propagation, In the VHF and UHF bands, radio waves can travel somewhat beyond the horizon due to refraction in the troposphere. This is due to changes in the index of air with temperature and pressure. At times, radio waves can travel up to 500 -1000 km due to tropospheric ducting and these effects are variable and not as reliable as ionospheric propagation, below. So radio waves directed at an angle into the sky can return to Earth beyond the horizon, by using multiple skips communication at intercontinental distances can be achieved
Radio wave
–
Diagram of the
electric fields (E) and
magnetic fields (H) of radio waves emitted by a
monopole radio transmitting
antenna (small dark vertical line in the center). The E and H fields are perpendicular as implied by the phase diagram in the lower right.
13.
Radio transmitter
–
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which generates a radio frequency alternating current. When a connected antenna is excited by this current, the antenna emits radio waves. The term transmitter is usually limited to equipment that generates radio waves for communication purposes, or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as ovens or diathermy equipment, are not usually called transmitters even though they often have similar circuits. The term is used more specifically to refer to a broadcast transmitter. This usage typically includes both the proper, the antenna, and often the building it is housed in. A transmitter can be a piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver, the term transmitter is often abbreviated XMTR or TX in technical documents. The purpose of most transmitters is radio communication of information over a distance, the transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, which is called the carrier signal. The information can be added to the carrier in several different ways, in an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude. In a frequency modulation transmitter, it is added by varying the signals frequency slightly. Many other types of modulation are used, the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as phones, walkie-talkies. In more powerful transmitters, the antenna may be located on top of a building or on a tower, and connected to the transmitter by a feed line. The first primitive radio transmitters were built by German physicist Heinrich Hertz in 1887 during his investigations of radio waves. These generated radio waves by a high voltage spark between two conductors, beginning in 1895 Guglielmo Marconi developed the first practical radio communication systems using spark transmitters. These spark-gap transmitters were used during the first three decades of radio, called the wireless telegraphy or spark era, vacuum tube transmitters took over because they were inexpensive and produced continuous waves, which could be modulated to transmit audio using amplitude modulation. This made possible commercial AM radio broadcasting, which began in about 1920, experimental television transmission had been conducted by radio stations since the late 1920s, but practical television broadcasting didnt begin until the 1940s
Radio transmitter
–
Continental 816R-5B 35 kW FM transmitter, belonging to American FM radio station KWNR broadcasting on 95.5 MHz in Las Vegas
Radio transmitter
–
Commercial
FM broadcasting transmitter at radio station
WDET-FM, Wayne State University, Detroit, USA. It broadcasts at 101.9
MHz with a radiated power of 48
kW.
Radio transmitter
–
Modern
amateur radio transceiver, the ICOM IC-746PRO. It can transmit on the amateur bands from 1.8 MHz to 144 MHz with an output power of 100 W
Radio transmitter
–
A
CB radio transceiver, a
two way radio transmitting on 27 MHz with a power of 4 W, that can be operated without a license
14.
Spark gap transmitter
–
A spark-gap transmitter is a device that generates radio frequency electromagnetic waves using a spark gap. Spark gap transmitters were the first devices to demonstrate practical radio transmission, later, more efficient transmitters were developed based on rotary machines like the high-speed Alexanderson alternators and the static Poulsen Arc generators. Even when vacuum tube based transmitters had been installed, many retained their crude. However, by 1940, the technology was no longer used for communication, use of the spark-gap transmitter led to many radio operators being nicknamed Sparks long after they ceased using spark transmitters. Even today, the German verb funken, literally, to spark, the effects of sparks causing unexplained action at a distance, such as inducing sparks in nearby devices, had been noticed by scientists and experimenters well before the invention of radio. Extensive experiments were conducted by Joseph Henry, Thomas Edison and David Edward Hughes, with no other theory to explain the phenomenon, it was usually written off as electromagnetic induction. Hertz used a spark gap transmitter and a tuned spark gap detector located a few meters from the source. Many experimenters used the spark gap setup to further investigate the new Hertzian wave phenomenon, including Oliver Lodge, the Italian inventor Guglielmo Marconi used a spark-gap transmitter in his experiments to develop the radio phenomenon into a wireless telegraphy system in the early 1890s. In 1895 he succeeded in transmitting over a distance of 1 1/4 miles and his first transmitter consisted of an induction coil connected between a wire antenna and ground, with a spark gap across it. Every time the induction coil pulsed, the antenna was momentarily charged up to tens of thousands of volts until the gap started to arc. This acted as a switch, essentially connecting the antenna to ground. While the various systems of spark transmitters worked well enough to prove the concept of wireless telegraphy. The biggest problem was that the power that could be transmitted was directly determined by how much electrical charge the antenna could hold. Because the capacitance of practical antennas is quite small, the way to get a reasonable power output was to charge it up to very high voltages. However, this made transmission impossible in rainy or even damp conditions, also, it necessitated a quite wide spark gap, with a very high electrical resistance, with the result that most of the electrical energy was used simply to heat up the air in the spark gap. Another problem with the transmitter was a result of the shape of the waveform produced by each burst of electromagnetic radiation. These transmitters radiated an extremely dirty wide band signal that could interfere with transmissions on nearby frequencies. Receiving sets relatively close to such a transmitter had entire sections of a band masked by this wide band noise, reginald Fessendens first attempts to transmit voice employed a spark transmitter operating at approximately 10,000 sparks/second
Spark gap transmitter
–
Pictorial diagram of a simple spark-gap transmitter showing examples of the early electronic components used. From a 1917 boy's book, it is typical of the low power transmitters homebuilt by thousands of amateurs to explore the exciting new technology of radio.
15.
Damped wave
–
A damped wave is a wave whose amplitude of oscillation decreases with time, eventually going to zero. This term also refers to a method of radio transmission produced by spark gap transmitters. Information was carried on this signal by telegraphy, turning the transmitter on, damped waves were the first practical means of radio communication, used during the wireless telegraphy era which ended around 1920. In radio engineering it is now referred to as Class B emission. However, such transmissions have a bandwidth and generate electrical noise which interferes with other radio transmissions. Continuous wave Damping On-off keying Amplitude modulation Types of radio emissions Sparks Telegraph Key Review A complete listing with photos of damped wave telegraph keys by manufacturer, 47cfr2.201 FCC rules where Type B damped wave emissions are forbidden
Damped wave
–
A series of damped waves, such as would be radiated by a
spark-gap transmitter. In this graph, the vertical axis is the amplitude of the wave, in units such as voltage or electric field strength; the horizontal axis is time.
16.
Frequency
–
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as frequency, which emphasizes the contrast to spatial frequency. The period is the duration of time of one cycle in a repeating event, for example, if a newborn babys heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as vibrations, audio signals, radio waves. For cyclical processes, such as rotation, oscillations, or waves, in physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν or ν. For a simple motion, the relation between the frequency and the period T is given by f =1 T. The SI unit of frequency is the hertz, named after the German physicist Heinrich Hertz, a previous name for this unit was cycles per second. The SI unit for period is the second, a traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. As a matter of convenience, longer and slower waves, such as ocean surface waves, short and fast waves, like audio and radio, are usually described by their frequency instead of period. Spatial frequency is analogous to temporal frequency, but the axis is replaced by one or more spatial displacement axes. Y = sin = sin d θ d x = k Wavenumber, in the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has a relationship to the wavelength. Even in dispersive media, the frequency f of a wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave. In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes, f = c λ. When waves from a monochrome source travel from one medium to another, their remains the same—only their wavelength. For example, if 71 events occur within 15 seconds the frequency is, the latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an error in the calculated frequency of Δf = 1/, or a fractional error of Δf / f = 1/ where Tm is the timing interval. This error decreases with frequency, so it is a problem at low frequencies where the number of counts N is small, an older method of measuring the frequency of rotating or vibrating objects is to use a stroboscope
Frequency
–
A resonant-reed frequency meter, an obsolete device used from about 1900 to the 1940s for measuring the frequency of alternating current. It consists of a strip of metal with reeds of graduated lengths, vibrated by an
electromagnet. When the unknown frequency is applied to the electromagnet, the reed which is
resonant at that frequency will vibrate with large amplitude, visible next to the scale.
Frequency
–
As time elapses – represented here as a movement from left to right, i.e. horizontally – the five
sinusoidal waves shown vary regularly (i.e. cycle), but at different
rates. The red
wave (top) has the lowest frequency (i.e. varies at the slowest rate) while the purple wave (bottom) has the highest frequency (varies at the fastest rate).
Frequency
Frequency
–
Modern frequency counter
17.
Bandwidth (signal processing)
–
Bandwidth is the difference between the upper and lower frequencies in a continuous set of frequencies. It is typically measured in hertz, and may refer to passband bandwidth, sometimes to baseband bandwidth. Passband bandwidth is the difference between the upper and lower frequencies of, for example, a band-pass filter, a communication channel. In the case of a filter or baseband signal, the bandwidth is equal to its upper cutoff frequency. A key characteristic of bandwidth is that any band of a given width can carry the amount of information. For example, a 3 kHz band can carry a telephone conversation whether that band is at baseband or modulated to some higher frequency, Bandwidth is a key concept in many telecommunications applications. In radio communications, for example, bandwidth is the range occupied by a modulated carrier signal. An FM radio receivers tuner spans a range of frequencies. A government agency may apportion the regionally available bandwidth to broadcast license holders so that their signals do not mutually interfere, each transmitter owns a slice of bandwidth. For different applications there are different precise definitions, which are different for signals than for systems. One definition of bandwidth, for a system, could be the range of frequencies over which the system produces a level of performance. A less strict and more practically useful definition will refer to the frequencies beyond which frequency response is small, small could mean less than 3 dB below the maximum value, or more rarely 10 dB below, or it could mean below a certain absolute value. As with any definition of the width of a function, many definitions are suitable for different purposes, in some contexts, the signal bandwidth in hertz refers to the frequency range in which the signals spectral density is nonzero or above a small threshold value. That definition is used in calculations of the lowest sampling rate that will satisfy the sampling theorem, the threshold value is often defined relative to the maximum value, and is most commonly the 3dB point, that is the point where the spectral density is half its maximum value. The word bandwidth applies to signals as described above, but it could apply to systems. To say that a system has a certain bandwidth means that the system can process signals of that bandwidth, or that the system reduces the bandwidth of a white noise input to that bandwidth. If the maximum gain is 0 dB, the 3 dB bandwidth is the range where the gain is more than −3 dB. This is also the range of frequencies where the gain is above 70. 7% of the maximum amplitude gain
Bandwidth (signal processing)
–
Baseband bandwidth. Here the bandwidth equals the upper frequency.
18.
Modulation
–
Most radio systems in the 20th century used frequency modulation or amplitude modulation to make the carrier carry the radio broadcast. Modulation of a sine waveform transforms a narrow frequency range baseband message signal into a passband signal, a modulator is a device that performs modulation. A demodulator is a device that performs demodulation, the inverse of modulation, a modem can perform both operations. The aim of digital modulation is to transfer a digital bit stream over an analog bandpass channel, in music synthesizers, modulation may be used to synthesise waveforms with an extensive overtone spectrum using a small number of oscillators. In this case the carrier frequency is typically in the order or much lower than the modulating waveform. In analog modulation, the modulation is applied continuously in response to the information signal. Where an AM carrier also carries a variable phase f. TM is f In digital modulation, a carrier signal is modulated by a discrete signal. Digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion, the changes in the carrier signal are chosen from a finite number of M alternative symbols. A simple example, A telephone line is designed for transferring audible sounds, for example tones, computers may however communicate over a telephone line by means of modems, which are representing the digital bits by tones, called symbols. If there are four symbols, the first symbol may represent the bit sequence 00, the second 01, the third 10. If the modem plays a melody consisting of 1000 tones per second, since each tone represents a message consisting of two digital bits in this example, the bit rate is twice the symbol rate, i. e.2000 bits per second. This is similar to the used by dialup modems as opposed to DSL modems. According to one definition of digital signal, the signal is a digital signal. According to another definition, the modulation is a form of digital-to-analog conversion, most textbooks would consider digital modulation schemes as a form of digital transmission, synonymous to data transmission, very few would consider it as analog transmission. The most fundamental digital modulation techniques are based on keying, PSK, FSK, a finite number of frequencies are used. ASK, a number of amplitudes are used. QAM, a number of at least two phases and at least two amplitudes are used
Modulation
–
Schematic of 4 baud (8 bit/s) data link containing arbitrarily chosen values.
Modulation
–
A low-frequency message signal (top) may be carried by an AM or FM radio wave.
19.
Frederick Thomas Trouton
–
Frederick Thomas Trouton FRS was an Irish physicist known for Troutons Rule and experiments to detect the Earths motion through the luminiferous aether. Trouton was born in Dublin on 24 November 1863, the youngest son of the wealthy and he attended Royal School Dungannon and went on to Trinity College, Dublin in 1884, where he studied engineering and physical science. While still a student, Trouton observed a relationship between boiling points and energies of vaporizations, which he presented in two short papers. He found the change of entropy per mole for vaporisation at a point is constant, or expressed mathematically ΔSm. This became known as Troutons Rule and, despite having some exceptions, is used to estimate the enthalpy of vaporization of liquids whose boiling points are known, Trouton himself belittled his discovery as it was merely the result of an afternoons manipulation of data from a book of tables. Before graduating he took a leading role in surveying for a railway. Trouton graduated Master of Arts and Doctor of Science in 1884 and they collaborated on many experiments and became good friends, FitzGeralds influence can be seen in a lot of Troutons earlier work. He was elected a Fellow of the Royal Society in June 1897 and he has made other important observations on the phase of secondary waves and on the influence of the size of the reflector in Hertzs equipment. A1902 appointment as Quain Professor of Physics at University College London led to a 12-year career of experimental physics and he received an OBE in 1918. Trouton married Anne Maria Fowler in 1887 and they had four sons and their first two sons, Eric and Desmond, were killed in World War I. He was severely ill in 1912, and an operation in 1914 left him paralysed in the lower limbs, despite this, he retained the wit and charm he was known for. After retiring, Trouton lived in Tilford, Surrey, and then Downe in Kent where he died on 21 September 1922
Frederick Thomas Trouton
–
Frederick Thomas Trouton
20.
Elihu Thomson
–
Elihu Thomson was an English-born American engineer and inventor who was instrumental in the founding of major electrical companies in the United States, the United Kingdom and France. He was born in Manchester on March 29,1853, Thomson attended Central High School in Philadelphia and graduated in 1870. Thomson took a position at Central, and in 1876, at the age of twenty-three. In 1880, he left Central to pursue research in the field of electrical engineering. With Edwin J. Houston, a teacher and later colleague of Thomsons at Central High School. Notable inventions created by Thomson during this period include a system, an automatically regulated three-coil dynamo, a magnetic lightning arrester. In 1892 the Thomson-Houston Electric Company merged with the Edison General Electric Company to become the General Electric Company, the historian Thomas P. Hughes writes that Thomson displayed methodological characteristics in the workshop and the laboratory as inventor and in the business world as entrepreneur. He also chose to solve problems in the expanding field of electric light. Thomsons name is commemorated by the British Thomson-Houston Company. Thomson was notable both for his emphasis on models and for the focus with which he pursued his research. Between 1880 and 1885, Thomson averaged twenty-one patent applications annually, at the Lynn GE plant, he worked with Edwin Rice and Sanford Moss and Charles Steinmetz. After being asked to become a director of GE, Thomson rejected the offer preferring continued research to management, Thomson was also president of the organization from 1889-90. Near the end of his life, Thomsons second wife Clarissa Hovey Thomson is reported to have said that she had to carry a basket with her to all of Thomsons awards. In 1889 he was decorated by the French Government for his electrical inventions and he received the honorary degree of A. M. from Yale. Tufts College in 1892 gave him the degree of Ph. D. and he was a founding member, as well as the second president, of the International Electrotechnical Commission. He served as acting president of MIT from 1920-1923, Thomson, overcoming his distaste for management accepted this role during a critical period for the university when it could not otherwise find a president. Thomson died at his estate in Swampscott, Massachusetts, the Elihu Thomson House in Swampscott was designated a U. S. National Historic Landmark in 1976 and serves as Swampscotts town hall. Thomson held more than 700 patents, Thomson used his patents to bolster his company, Thomson-Houston Company, later General Electric
Elihu Thomson
–
Subsidiaries and
divisions
Elihu Thomson
–
Elihu Thomson
21.
Nikola Tesla
–
He immigrated to the United States in 1884, where he would become a naturalized citizen. He worked for a time at the Edison Machine Works in New York City before he struck out on his own. With the help of partners to finance and market his ideas, attempting to develop inventions he could patent and market, Tesla conducted a range of experiments with mechanical oscillators/generators, electrical discharge tubes, and early X-ray imaging. He also built a boat, one of the first ever exhibited. Tesla became well known as an inventor and would demonstrate his achievements to celebrities and wealthy patrons at his lab, in 1893, he made pronouncements on the possibility of wireless communication with his devices. After Wardenclyffe, Tesla went on to try and develop a series of inventions in the 1910s and 1920s with varying degrees of success, having spent most of his money, he lived in a series of New York hotels, leaving behind unpaid bills. The nature of his work and the pronouncements he made to the press later in life earned him the reputation of an archetypal mad scientist in American popular culture. Tesla died in New York City in January 1943 and his work fell into relative obscurity following his death, but in 1960, the General Conference on Weights and Measures named the SI unit of magnetic flux density the tesla in his honor. There has been a resurgence in popular interest in Tesla since the 1990s, Tesla was born on 10 July 1856 into a Serb family in the village of Smiljan, Austrian Empire. His father, Milutin Tesla, was an Orthodox priest, Teslas mother, Đuka Tesla, whose father was also an Orthodox priest, had a talent for making home craft tools and mechanical appliances and the ability to memorize Serbian epic poems. Đuka had never received a formal education, Tesla credited his eidetic memory and creative abilities to his mothers genetics and influence. Teslas progenitors were from western Serbia, near Montenegro, Tesla was the fourth of five children. He had a brother, Dane, and three sisters, Milka, Angelina and Marica. Dane was killed in an accident when Tesla was aged five. In 1861 Tesla attended primary school in Smiljan, where he studied German, arithmetic, in 1862 the Tesla family moved to Gospić, Austrian Empire, where Teslas father worked as parish priest. Nikola completed primary school, followed by middle school, in 1870 Tesla moved to Karlovac to attend school at the Higher Real Gymnasium. The classes were held in German, as it was a school within the Austro-Hungarian Military Frontier, Tesla would later write that he became interested in demonstrations of electricity by his physics professor. Tesla noted that these demonstrations of this mysterious phenomena made him want to more of this wonderful force
Nikola Tesla
–
Tesla, aged 34, 1890, photo by
Napoleon Sarony
Nikola Tesla
–
Rebuilt, Tesla's house (parish hall) in
Smiljan,
Croatia, where he was born, and the rebuilt church, where his father served. During the
Yugoslav Wars, several of the buildings were severely damaged by fire. They were restored and reopened in 2006.
Nikola Tesla
–
Nikola Tesla's father Milutin,
Orthodox priest in the village of
Smiljan
Nikola Tesla
–
Tesla aged 23, c. 1879
22.
Reginald Fessenden
–
Reginald Aubrey Fessenden was a Canadian-born inventor, who did a majority of his work in the United States and also claimed U. S. citizenship through his American-born father. During his life he received hundreds of patents in fields, most notably ones related to radio. Fessenden is best known for his work developing radio technology. His achievements included the first transmission of speech by radio, in 1932 he reported that, in late 1906, he also made the first radio broadcast of entertainment and music, although a lack of verifiable details has led to some doubts about this claim. Reginald Fessenden was born October 6,1866, in East-Bolton, Quebec, Elisha Fessenden was a Church of England in Canada minister, and the family moved to a number of postings throughout the province of Ontario. While growing up, Fessenden attended a number of educational institutions, at the age of nine, he was enrolled in the DeVeaux Military school for a year. He next attended Trinity College School in Port Hope, Ontario and he also spent a year working for the Imperial Bank at Woodstock, because he had not yet reached the age of 16 needed to enroll in college. At the age of fourteen, Bishops College School in Lennoxville, Quebec, thus, while Fessenden was still a teenager, he taught mathematics to the younger students at the School, while simultaneously studying with older students at the College. While in Bermuda, he engaged to Helen Trott. They married in September 1890 and later had a son, Reginald Kennelly Fessenden, Fessendens classical education provided him with only a limited amount of scientific and technical training. Interested in increasing his skills in the field, he moved to New York City in 1886, with hopes of gaining employment with the famous inventor. He quickly proved his worth, and received a series of promotions, in late 1886, Fessenden began working directly for Edison at the inventors new laboratory in West Orange, New Jersey as a junior technician. He participated in a range of projects, which included work in solving problems in chemistry, metallurgy. However, in 1890, facing problems, Edison was forced to lay off most of the laboratory employees. Taking advantage of his recent practical experience, Fessenden was able to find positions with a series of manufacturing companies, by 1899 he was able to send radiotelegraph messages between Pittsburgh and Allegheny City, using a receiver of his own design. The provisions of his contract called for him to be paid $3,000 per year, and provided with space, assistance. The agreement gave the Weather Bureau access to any devices Fessenden developed, Fessenden quickly made major advances, especially in receiver design, as he worked to develop audio reception of signals. Fessendens initial Weather Bureau work took place at Cobb Island, Maryland, located in the Potomac River about 80 kilometers downstream from Washington, as the experimentation expanded, additional stations were built along the Atlantic Coast in North Carolina and Virginia
Reginald Fessenden
–
The Father of Radio Broadcasting
Reginald Fessenden
–
Commemorative plaque near Fessenden's birthplace
Reginald Fessenden
–
Cobb Island on the Potomac River, scene of the first successful radio transmission of speech on December 23, 1900.
Reginald Fessenden
–
Photograph of Rotary Gap transmitter at Brant Rock, MA (c.1906)
23.
General Electric
–
General Electric, often abbreviated as GE, is an American multinational conglomerate corporation incorporated in New York and headquartered in Boston, Massachusetts. In 2011, GE ranked among the Fortune 500 as the 68th-largest firm in the U. S. by gross revenue, as of 2012, the company was listed the fourth-largest in the world among the Forbes Global 2000, further metrics being taken into account. The Nobel Prize has twice been awarded to employees of General Electric, Irving Langmuir in 1932, on January 13,2016, it was announced that GE will be moving its corporate headquarters from Fairfield, Connecticut to the South Boston Waterfront neighborhood of Boston, Massachusetts. The first group of workers arrived in the summer of 2016, morgan and the Vanderbilt family for Edisons lighting experiments. The new company also acquired Sprague Electric Railway & Motor Company in the same year, both plants continue to operate under the GE banner to this day. The company was incorporated in New York, with the Schenectady plant used as headquarters for years thereafter. Around the same time, General Electrics Canadian counterpart, Canadian General Electric, was formed, in 1896, General Electric was one of the original 12 companies listed on the newly formed Dow Jones Industrial Average. After 120 years, it is the one of the original companies still listed on the Dow index. In 1911, General Electric absorbed the National Electric Lamp Association into its lighting business, GE established its lighting division headquarters at Nela Park in East Cleveland, Ohio. Nela Park is still the headquarters for GEs lighting business, owen D. Young, through GE, founded the Radio Corporation of America in 1919 to further international radio. GE used RCA as its retail arm for radio sales from 1919, in 1927, Ernst Alexanderson of GE made the first demonstration of his television broadcasts at his General Electric Realty Plot home at 1132 Adams Rd, Schenectady, NY. The sound was broadcast on GEs WGY, experimental television station W2XAD evolved into station WRGB which—along with WGY and WGFM —was owned and operated by General Electric until 1983. GEs history of working with turbines in the field gave them the engineering know-how to move into the new field of aircraft turbosuperchargers. Led by Sanford Alexander Moss, GE introduced the first superchargers during World War I, superchargers became indispensable in the years immediately prior to World War II, and GE was the world leader in exhaust-driven supercharging when the war started. This experience, in turn, made GE a natural selection to develop the Whittle W.1 jet engine that was demonstrated in the United States in 1941, GE ranked ninth among United States corporations in the value of wartime production contracts. In 2002, GE acquired the assets of Enron during its bankruptcy proceedings. Some consumers boycotted GE light bulbs, refrigerators and other products in the 1980s and 1990s to protest GEs role in weapons production. With IBM, Burroughs, NCR, Control Data Corporation, Honeywell, RCA and UNIVAC, GE had a line of general purpose and special purpose computers
General Electric
–
General Electric in Schenectady, NY, aerial view, 1896
General Electric
–
General Electric Company
General Electric
–
Plan of Schenectady plant, 1896
General Electric
–
A 23-ton
diesel-electric locomotive made at the General Electric Corp. plant in
Schenectady, New York
24.
Radio communication
–
When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form, Radio systems need a transmitter to modulate some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation. Radio systems also need an antenna to convert electric currents into radio waves, an antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allow individual stations to be selected, the electromagnetic wave is intercepted by a tuned receiving antenna. Radio frequencies occupy the range from a 3 kHz to 300 GHz, a radio communication system sends signals by radio. The term radio is derived from the Latin word radius, meaning spoke of a wheel, beam of light, however, this invention would not be widely adopted. The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world, the United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram, the term started to become preferred by the general public in the 1920s with the introduction of broadcasting. Radio systems used for communication have the following elements, with more than 100 years of development, each process is implemented by a wide range of methods, specialised for different communications purposes. Each system contains a transmitter, This consists of a source of electrical energy, the transmitter contains a system to modulate some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle such as amplitude, frequency, phase. Amplitude modulation of a carrier wave works by varying the strength of the signal in proportion to the information being sent. For example, changes in the strength can be used to reflect the sounds to be reproduced by a speaker. It was the used for the first audio radio transmissions. Frequency modulation varies the frequency of the carrier, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. FM has the capture effect whereby a receiver only receives the strongest signal, Digital data can be sent by shifting the carriers frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at Very high frequency radio frequencies for high-fidelity broadcasts of music, analog TV sound is also broadcast using FM. Angle modulation alters the phase of the carrier wave to transmit a signal
Radio communication
–
The
Alexandra Palace radio transmitter mast
Radio communication
–
Classic radio
receiver dial
Radio communication
–
Rooftop
television antennas.
Yagi-Uda antennas like these six are widely used at
VHF and
UHF frequencies.
Radio communication
–
Bakelite radio at the Bakelite Museum, Orchard Mill, Williton, Somerset, UK.
25.
Brant Rock, Massachusetts
–
The population of the CDP was 4,970 at the 2010 census. Brant Rock and Ocean Bluff were originally inhabited by Native Americans, Native American artifacts have been found extensively in the area. The main road through the area, known today as Ocean Street, is a Native American road, the area at the end of Brant Rock village, known as Blackmans Point, was a Native American campground. In the 1630s, the government of the Pilgrim settlers at Plymouth began to give out land grants in the area, the Ocean Bluff area was first granted to the governor of the Pilgrims. It was known by about 1638 as Governors Island, later on in the 17th century, it became known as Winters Island. Christopher Winter was later tried in Plymouth Court for the crime of fathering his own grandchild, eventually, his daughter married a man named John Hewitt, and he became the owner of Winters Island. For many generations the area was known as Hewitts Island, or Hewitts Point, however, today most residents refer to the area as Ocean Bluff. Brant Rock was originally known as Branchs Island, the name Brant Rock eventually came into use, because of the huge rock outcropping along the beach on which brant geese would tend to rest. From the 17th century through the late 19th century, the area was used for salt marsh haying, cattle grazing. In the late 19th century, the area populated by large summer resort hotels. Hewitts Island and Branchs Island were sometimes referred to as the Spectacle Islands, after the Green Harbor Dyke was built following the Civil War, the tidal salt marshes in the area dried up. The Spectacle Islands were no longer surrounded by water from the flooding of the marshes. In January 1906, Reginald Fessenden achieved the first two-way transatlantic radiotelegraph transmission, on Christmas Eve, December 24,1906, Fessenden transmitted from Brant Rock Station the first audio radio broadcast of music and entertainment in history. Radio operators on ships in the Atlantic heard a broadcast that included Fessenden playing the song O Holy Night on the violin, Ocean Bluff and Brant Rock are located at 42°6′6″N 70°39′39″W, and are part of the town of Marshfield. According to the United States Census Bureau, the CDP has an area of 11.3 km2, of which 5.3 km2 is land and 6.0 km2 is water. Ocean Bluff and Brant Rock contain six public beaches, Sunrise Beach, Ocean Bluff Beach, Rebar Beach, Brant Rock Beach, Blackmans Point, and Bluefish Cove. All of these beaches, as well as the rest of the Marshfield seashore from Green Harbor village to Rexhame village, were known by the name of Marshfield Beach. During the summer time, especially along Sunrise Beach and Ocean Bluff, Ocean Bluff locals have made a name for their neighborhood and home beach down the east coast, competing in skim contests
Brant Rock, Massachusetts
–
Ocean Bluff looking south
Brant Rock, Massachusetts
–
Postcard image, from around 1910, of the 420-foot-tall (128 m) Brant Rock radio tower
Brant Rock, Massachusetts
–
Although Fessenden's antenna in Brant Rock was demolished in 1917, the insulated base on which it stood still survives. The layers of concrete were originally separated by arrays of ceramic insulators.
26.
John Hays Hammond, Jr.
–
John Hays Hammond Jr. was an American inventor known as The Father of Radio Control. Of Hammond’s many individual inventions, the inventions which have seen the most significant application are the variable pitch or controlled pitch propellers and he was the son of mining engineer John Hays Hammond, Sr. Born in San Francisco, California, his family moved to South Africa and his father was active as a mining engineer for Cecil Rhodes mines in South Africa. In 1898, the moved to England, where young Hammond fell in love with castles. The family returned to the United States at the turn of the 20th century, at the age of twelve, Hammond accompanied his father on a business trip to Thomas Edison’s laboratory in West Orange, New Jersey. Upon being introduced to Edison, the boy asked so many questions that the inventor gave him a tour of the complex. The two would remain in contact for the rest of Edison’s life, while studying at the Sheffield Scientific School of Yale University, Hammond became interested in the new study of radio waves and he was taken under the wing of Alexander Graham Bell. Bell also became his mentor and the two would remain friends until Bell’s death. After graduation from Yale in 1910, Hammond took a job in the U. S and his strategy was simple, having learned from Edison that inventing had to be a money-making proposition, where better to learn what fields were up-and-coming than in the Patent Office. After he became an authority on the patent process, he founded the Hammond Radio Research Laboratory on his father’s estate in Gloucester, Massachusetts. In total, he is credited with more than 800 foreign and domestic patents on more than 400 inventions mostly in the fields of radio control and naval weaponry. He served on the Board of Directors of RCA and a listing of his colleagues and society friends reads like a Who’s Who of the rich. Aside from his wealth, his inventions brought Hammond an additional fortune. Between the years 1926 and 1929, he built a castle which became his home, laboratory, and a showplace for his collection of Roman, medieval, and Renaissance artifacts. Hammond was also interested in the mechanism and workings of the pipe organ, famous organists, including Richard Ellsasser and Virgil Fox, performed and made commercial recordings on this instrument, unfortunately no longer in operating condition. A biography of John Hays Hammond Jr. entitled Living in the Past, Hammond also appears as a character in several of Dandola’s mystery novels which are set during World War II. Hammond was awarded the Edward Longstreth Medal from The Franklin Institute in Philadelphia, Pennsylvania in 1959 and his castle was investigated by TAPS in 2012 for paranormal activity and this was shown on the TV show Ghost Hunters. Hammond Castle was also featured on the PBS Reality Show FETCH. with Ruff Ruffman in Season One
John Hays Hammond, Jr.
–
May 22, 1922
John Hays Hammond, Jr.
–
John Hays Hammond, Jr. & Sr., 1922
27.
Gloucester, Massachusetts
–
Gloucester /ˈɡlɒstər/ is a city on Cape Ann in Essex County, Massachusetts, in the United States. It is part of Massachusetts North Shore, the population was 28,789 at the 2010 U. S. Census. The boundaries of Gloucester originally included the town of Rockport, in an area dubbed Sandy Bay and that village separated formally on February 27,1840. In 1873, Gloucester was reincorporated as a city, Gloucester was founded at Cape Ann by an expedition called the Dorchester Company of men from Dorchester chartered by James I in 1623. It was one of the first English settlements in what would become the Massachusetts Bay Colony, the first company of pioneers made landing at Half Moon Beach and settled nearby, setting up fishing stages in a field in what is now Stage Fort Park. This settlements existence is proclaimed today by a tablet, affixed to a 50-foot boulder in that park. Life in this first settlement was harsh and it was short-lived, around 1626 the place was abandoned, and the people removed themselves to Naumkeag, where more fertile soil for planting was to be found. The meetinghouse was even disassembled and relocated to the new place of settlement, at some point in the following years – though no record exists – the area was slowly resettled. The town was incorporated in 1642. It is at time that the name Gloucester first appears on tax rolls. This new permanent settlement focused on the Town Green area, an inlet in the marshes at a bend in the Annisquam River and this area is now the site of Grant Circle, a large traffic rotary at which Massachusetts Route 128 mingles with a major city street. Here the first permanent settlers built a house and therefore focused the nexus of their settlement on the Island for nearly 100 years. Unlike other early coastal towns in New England, development in Gloucester was not focused around the harbor as it is today and this is evidenced by the placement of the Town Green nearly two miles from the harbor-front. The Town Green is also where the built the first school. By Massachusetts Bay Colony Law, any town boasting 100 families or more had to provide a public schoolhouse and this requirement was met in 1698, with Thomas Riggs standing as the towns first schoolmaster. The White-Ellery House was erected in 1710 upon the Town Green and it was built at the edge of a marsh for Gloucester’s first settled minister, the Reverend John White. Early industry included subsistence farming and logging, because of the poor soil and rocky hills, Cape Ann was not well suited for farming on a large scale. Small family farms and livestock provided the bulk of the sustenance to the population, Fishing, for which the town is known today, was limited to close-to-shore, with families subsisting on small catches as opposed to the great bounties yielded in later years
Gloucester, Massachusetts
–
Man at the Wheel, Fisherman's Memorial Cenotaph
Gloucester, Massachusetts
–
Gloucester Harbor, ca. 1877,
William Morris Hunt
Gloucester, Massachusetts
–
1893 map of Gloucester
Gloucester, Massachusetts
–
Fish Dressing Wharf c. 1908
28.
New Brunswick, New Jersey
–
The City of New Brunswick is a city in Middlesex County, New Jersey, United States. It is the county seat of Middlesex County, and the home of Rutgers University, the city is located on the Northeast Corridor rail line,27 miles southwest of Manhattan, on the southern bank of the Raritan River. The corporate headquarters and production facilities of several global companies are situated in the city, including Johnson & Johnson. New Brunswick is noted for its ethnic diversity, at one time, one quarter of the Hungarian population of New Jersey resided in the city and in the 1930s one out of three city residents was Hungarian. The Hungarian community continues to exist, alongside growing Asian and Hispanic communities that have developed around French Street near Robert Wood Johnson University Hospital and it was first inhabited by the Lenape Native Americans. The first European settlement at the site of New Brunswick was made in 1681, the settlement here was called Prigmores Swamp, then known as Inians Ferry. In 1714, the settlement was given the name New Brunswick, after the city of Braunschweig, in state of Lower Saxony, in Germany. Braunschweig was an influential and powerful city in the Hanseatic League, later in the Holy Roman Empire, and was an administrative seat for the Duchy of Hanover. Shortly after the first settlement of New Brunswick in colonial New Jersey, George, Duke of Brunswick-Lüneburg, alternatively, the city gets its name from King George II of Great Britain, the Duke of Brunswick-Lüneburg. New Brunswick was incorporated as a town in 1736 and chartered as a city in 1784 and it was incorporated into a town in 1798 as part of the Township Act of 1798. It was occupied by the British in the winter of 1776–1777 during the Revolutionary War. The Declaration of Independence received one of its first public readings, by Col. John Neilson, in New Brunswick on July 9,1776, in the days following its promulgation by the Continental Congress. The Trustees of Queens College, founded in 1766, voted to locate the college in New Brunswick, selecting the city over Hackensack, in Bergen County. Classes began in 1771 with one instructor, one sophomore, Matthew Leydt, classes were held through the American Revolution in various taverns and boarding houses, and at a building known as College Hall on George Street, until Old Queens was erected in 1808. It remains the oldest building on the Rutgers University campus, the Queens College Grammar School was established also in 1766, and shared facilities with the College until 1830, when it located in a building across College Avenue from Old Queens. The New Brunswick Theological Seminary, founded in 1784 in New York, moved to New Brunswick in 1810, New Brunswick was incorporated as a city by an act of the New Jersey Legislature on September 1,1784. The existence of an African American community dates back to the late 18th century, the citys Mount Zion African Methodist Episcopal Church, located at 39 Morris Street, was originally established in 1825 at 25 Division Street, making it one of the oldest in New Jersey. New Brunswick began attracting a Hungarian immigrant population around the turn of the 20th century, hungarians were primarily attracted to the city by employment at Johnson & Johnson factories located in the city
New Brunswick, New Jersey
–
New Brunswick, New Jersey
New Brunswick, New Jersey
–
Early nineteenth century drawing of Old Queen's
New Brunswick, New Jersey
–
New Brunswick and the Raritan River, 1903
New Brunswick, New Jersey
–
The Committee of Hungarian Churches and Organizations of New Brunswick commemorating the anniversary of the
Hungarian Revolution of 1956
29.
Vacuum-tube
–
In electronics, a vacuum tube, an electron tube, or just a tube, or valve, is a device that controls electric current between electrodes in an evacuated container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by the filament and this type is called a thermionic tube or thermionic valve. A phototube, however, achieves electron emission through the photoelectric effect, the simplest vacuum tube, the diode, contains only a heater, a heated electron-emitting cathode, and a plate. Current can only flow in one direction through the device between the two electrodes, as electrons emitted by the travel through the tube and are collected by the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids, Tubes with grids can be used for many purposes, including amplification, rectification, switching, oscillation, and display. In the 1940s the invention of devices made it possible to produce solid-state devices, which are smaller, more efficient, more reliable, more durable. Hence, from the mid-1950s solid-state devices such as transistors gradually replaced tubes, the cathode-ray tube remained the basis for televisions and video monitors until superseded in the 21st century. However, there are still a few applications for which tubes are preferred to semiconductors, for example, the used in microwave ovens. One classification of vacuum tubes is by the number of active electrodes, a device with two active elements is a diode, usually used for rectification. Devices with three elements are used for amplification and switching. Additional electrodes create tetrodes, pentodes, and so forth, which have additional functions made possible by the additional controllable electrodes. X-ray tubes are vacuum tubes. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission, since these sorts of vacuum tubes have functions other than electronic amplification and rectification they are described in their own articles. A vacuum tube consists of two or more electrodes in a vacuum inside an airtight enclosure, most tubes have glass envelopes, though ceramic and metal envelopes have been used. The electrodes are attached to leads which pass through the envelope via an airtight seal, Tubes were a frequent cause of failure in electronic equipment, and consumers were expected to be able to replace tubes themselves. In addition to the terminals, some tubes had an electrode terminating at a top cap. The principal reason for doing this was to avoid leakage resistance through the tube base, the bases were commonly made with phenolic insulation which performs poorly as an insulator in humid conditions. There was even a design that had two top cap connections
Vacuum-tube
–
Modern vacuum tubes, mostly miniature style
Vacuum-tube
–
One of Edison's experimental bulbs
Vacuum-tube
–
Fleming's first diodes
Vacuum-tube
–
The first triode, the De Forest
Audion, invented in 1906
30.
Electronic oscillator
–
An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave. Oscillators convert direct current from a supply to an alternating current signal. They are widely used in electronic devices. Oscillators are often characterized by the frequency of their output signal and this term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator. An audio oscillator produces frequencies in the range, about 16 Hz to 20 kHz. An RF oscillator produces signals in the frequency range of about 100 kHz to 100 GHz. Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters, there are two main types of electronic oscillator, the linear or harmonic oscillator and the nonlinear or relaxation oscillator. The harmonic, or linear, oscillator produces a sinusoidal output, when the power supply to the amplifier is first switched on, electronic noise in the circuit provides a non-zero signal to get oscillations started. The noise travels around the loop and is amplified and filtered until very quickly it converges on a wave at a single frequency. RC oscillators are used to generate lower frequencies, for example in the audio range. Common types of RC oscillator circuits are the phase shift oscillator, in an LC oscillator circuit, the filter is a tuned circuit consisting of an inductor and capacitor connected together. Charge flows back and forth between the plates through the inductor, so the tuned circuit can store electrical energy oscillating at its resonant frequency. There are small losses in the circuit, but the amplifier compensates for those losses and supplies the power for the output signal. Typical LC oscillator circuits are the Hartley, Colpitts and Clapp circuits, in a crystal oscillator circuit the filter is a piezoelectric crystal. The crystal mechanically vibrates as a resonator, and its frequency of vibration determines the oscillation frequency, crystals have very high Q-factor and also better temperature stability than tuned circuits, so crystal oscillators have much better frequency stability than LC or RC oscillators. Crystal oscillators are the most common type of linear oscillator, used to stabilize the frequency of most radio transmitters, crystal oscillators often use the same circuits as LC oscillators, with the crystal replacing the tuned circuit, the Pierce oscillator circuit is also commonly used. Quartz crystals are generally limited to frequencies of 30 MHz or below, other types of resonator, dielectric resonators and surface acoustic wave devices, are used to control higher frequency oscillators, up into the microwave range. For example, SAW oscillators are used to generate the signal in cell phones
Electronic oscillator
–
1 MHz electronic oscillator circuit which uses the resonant properties of an internal quartz crystal to control the frequency. Provides the
clock signal for digital devices such as computers.
Electronic oscillator
–
A popular
op-amp relaxation oscillator.
Electronic oscillator
–
(left) Typical block diagram of a negative resistance oscillator. In some types the negative resistance device is connected in parallel with the resonant circuit. (right) A negative resistance microwave oscillator consisting of a
Gunn diode in a
cavity resonator. The negative resistance of the diode excites microwave oscillations in the cavity, which radiate out the aperture into a
waveguide.
Electronic oscillator
–
A 120 MHz oscillator from 1938 using a parallel rod
transmission line resonator (
Lecher line). Transmission lines are widely used for UHF oscillators.
31.
Armstrong oscillator
–
The Armstrong oscillator is an LC electronic oscillator circuit which uses an inductor and capacitor to generate an oscillation. The result is a narrow-band radio-frequency filter and amplifier, the non-linear characteristic of the transistor or tube also demodulated the RF signal to produce the audio signal. The circuit diagram shown is an implementation, using a field-effect transistor as the amplifying element. Armstrongs original design used a vacuum tube. Note that in the Meissner variant, the LC resonant circuit is exchanged with the feedback coil, many publications, however, embrace both variants with either name. Apparently, the English speakers using Armstrong, and the German speakers Meißner
Armstrong oscillator
–
Transistor Armstrong oscillator schematic
32.
Radio
–
When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form, Radio systems need a transmitter to modulate some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation. Radio systems also need an antenna to convert electric currents into radio waves, an antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allow individual stations to be selected, the electromagnetic wave is intercepted by a tuned receiving antenna. Radio frequencies occupy the range from a 3 kHz to 300 GHz, a radio communication system sends signals by radio. The term radio is derived from the Latin word radius, meaning spoke of a wheel, beam of light, however, this invention would not be widely adopted. The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world, the United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram, the term started to become preferred by the general public in the 1920s with the introduction of broadcasting. Radio systems used for communication have the following elements, with more than 100 years of development, each process is implemented by a wide range of methods, specialised for different communications purposes. Each system contains a transmitter, This consists of a source of electrical energy, the transmitter contains a system to modulate some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle such as amplitude, frequency, phase. Amplitude modulation of a carrier wave works by varying the strength of the signal in proportion to the information being sent. For example, changes in the strength can be used to reflect the sounds to be reproduced by a speaker. It was the used for the first audio radio transmissions. Frequency modulation varies the frequency of the carrier, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. FM has the capture effect whereby a receiver only receives the strongest signal, Digital data can be sent by shifting the carriers frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at Very high frequency radio frequencies for high-fidelity broadcasts of music, analog TV sound is also broadcast using FM. Angle modulation alters the phase of the carrier wave to transmit a signal
Radio
–
The
Alexandra Palace radio transmitter mast
Radio
–
Classic radio
receiver dial
Radio
–
Rooftop
television antennas.
Yagi-Uda antennas like these six are widely used at
VHF and
UHF frequencies.
Radio
–
Bakelite radio at the Bakelite Museum, Orchard Mill, Williton, Somerset, UK.
33.
VLF transmitter Grimeton
–
The Varberg Radio Station at Grimeton is a VLF transmission facility at Grimeton close to Varberg, in Halland, Sweden. It has the only working Alexanderson alternator rotating armature radio transmitter in the world and is classified as a World Heritage Site and it is an anchor site for the European Route of Industrial Heritage. The transmitter was built in 1922 to 1924, to operate at 17.2 kHz, the Grimeton VLF transmitter location is also used for shortwave transmissions, FM and TV broadcasting. For this purpose, a 260 metre high guyed steel framework mast was built in 1966 next to the containing the 40 kHz transmitter. Until the 1950s, the Grimeton VLF transmitter was used for radio telegraphy to Radio Central in Long Island, New York. From the 1960s until 1996 it transmitted orders to submarines in the Swedish Navy, in 1968 a second transmitter was installed which uses the same aerial as the machine transmitter but with transistor and tube technology. The Alexanderson transmitter became obsolete in 1996 and went out of service, however, because it was still in good condition it was declared a national monument and can be visited during the summer. On July 2,2004, the Grimeton VLF transmitter was declared a World Cultural Heritage site by UNESCO and it continues to be used on special occasions such as Alexanderson Day to transmit Morse messages on 17.2 kHz. The Grimeton/Varberg site is used by the Swedish Navy, transmitting on 40.4 kHz using call sign SRC using the vacuum tube transmitter. Therefore the special transmissions from that machine transmitter are very rare, recent transmissions from SAQ on 17.2 kHz took place on December 24,2013, June 29,2014, December 24,2014, June 28,2015 and July 3,2016. At least two regular transmissions take place each year, on the first Sunday of July and on Christmas Eve, plus one or two extra transmissions on special occasions or for testing
VLF transmitter Grimeton
–
UNESCO World Heritage Site
VLF transmitter Grimeton
–
Alexanderson alternator in the Grimeton VLF transmitter. The drive motor is at the extreme right; the speed-increaser gearbox is just to its left. Note the bronze-colored shaft coupling.
34.
Rocky Point, New York
–
Rocky Point is a hamlet and census-designated place in Suffolk County, New York on the North Shore of Long Island. As of the 2010 United States Census, the CDP population was 14,014, Rocky Point is a community in the Town of Brookhaven. Rocky Point is home to the site where American radio company RCA once operated a very large transmitting and transmitter research facility, RCA began to transmit transatlantic radio messages from Radio Central after its opening on November 5,1921. Early Radio Central transmissions were received by many European nations, including Britain, Spain, France, Germany, Italy, Austria, on January 7,1927, AT&T initiated the first transatlantic commercial telephone service, linking London and New York. AT&Ts transmitter was at Radio Central, and their receiver was in Houlton, the radiotelephone signal from Radio Central was received by the British General Post Offices receiver facility in Cupar, Scotland. Radio Central was one of the original operating and touring sites of Guglielmo Marconis radio shack. The 5, 200-acre Rocky Point site was decommissioned and demolished in the 1970s and it now consists of many concrete ruins and downed telephone poles and radio towers, owned by the New York State Department of Environmental Conservation. It is part of the Rocky Point Natural Resources Management Area, the site gives an interesting insight into the 1920s, because—being in the middle of the forest—the footprints of the site remain largely untouched since its operational period. The western terminus of the 125-mile-long Paumanok Path hiking trail is in the forest, a secret project housed in Radio Centrals building #10 became the worlds first color television. Rocky Point, along with neighboring village Shoreham, was also the home to inventor, Rocky Point is the home of the only paragliding site on Long Island. The community is on the North Shore of Long Island, according to the United States Census Bureau, the CDP has a total area of 11.3 square miles, all land. As of the census of 2010, there were 14,014 people,4,820 households, the population density was 1,240.2 per square mile. There were 5,366 housing units at a density of 474. 9/sq mi. The racial makeup of the CDP was 93. 7% White,1. 5% Black or African American,0. 1% Native American,1. 6% Asian,0. 04% Pacific Islander,1. 6% some other race, and 1. 4% from two or more races. Hispanic or Latino of any race were 7. 0% of the population,19. 6% of all households were made up of individuals, and 5. 7% were someone living alone who was 65 years of age or older. The average household size was 2.89, and the family size was 3.34. In the CDP, the population was out with 27. 2% under the age of 18,8. 1% from 18 to 24,28. 8% from 25 to 44,27. 2% from 45 to 64. The median age was 36.8 years, for every 100 females there were 98.7 males
Rocky Point, New York
–
The c. 1721 Noah Hallock homestead, the oldest extant structure in Rocky Point
Rocky Point, New York
–
Rocky Point Landing
35.
Goldschmidt alternator
–
Radio alternators like the Goldschmidt were some of the first continuous wave radio transmitters. Although the device was a transmitter, it resembled an electric generator used to produce electric power in a power plant. Like other generators it consisted of a rotor, several feet in diameter, wound with coils of wire, the interaction between the magnetic fields of the rotor and stator produced radio frequency currents in the stator windings, which were applied to the antenna. The Goldschmidt alternator was turned by a powerful DC electric motor attached to the shaft, Goldschmidt transmitters operated at longwave frequencies of about 20 to 100 kHz. Only alternator transmitters like the Goldschmidt and Alexanderson could produce the high powers necessary to communicate reliably at transoceanic distances, the Goldschmidt was a less widely used design, mostly used in European stations. Around 1900 it was realized that the technology for generating radio waves. In 1906 Reginald Fessenden and Ernst Alexanderson at General Electric began to solve the problems and build alternators which could produce frequencies in the radio range and it was 1916 before Alexanderson machines achieved the high power needed for transatlantic communication, and they were extremely complex and expensive. In 1908 Westinghouse engineer Rudolph Goldschmidt devised a method to enable an alternator to generate high frequency without requiring excessive speeds. His technique was to exploit resonance and the nonlinear saturation characteristic of the rotor to use the alternator as a frequency multiplier as well as a generator. The output frequency of the Goldschmidt alternator was f = N P U where N was a small integer, N was limited to 4 in most practical machines, as losses due to leakage flux increased rapidly with increasing N. Thus a 100 kHz Goldschmidt machine with P =300 poles would require a speed of only U =5000 RPM. No rotor of this construction had ever used in a large machine. The limit of output frequency for Goldschmidt alternators, as well as other technologies, was about 200 kHz. The machine was developed and manufactured by the German company Hochfrequenz-Maschinen Aktiengesellschaft für Drahtlose Telegraphie and was used in Europe. The first Goldschmidt machine in the UK, a 12 kW,60 kHz transmitter was installed at Stough in 1912. A100 kW,400 pole unit was put into operation at Eilvese, Neustadt-am-Ruebenberger, Germany, a 250 kW unit installed at Laeken, Belgium in 1913 to communicate with Belgiums African colonies was destroyed by the Germans in 1914. The heyday of the big alternator radio transmitters was around 1918, world War I had brought home to nations the strategic importance of radio communication, as without it they could easily be isolated by enemies cutting their submarine telegraph cables. This precipitated a postwar building boom of large transcontinental alternater radio stations, however these expensive behemoths were obsolete even as they were installed
Goldschmidt alternator
Goldschmidt alternator
–
12.5 kW Goldschmidt alternator installed in 1910 at a wireless station in Eberswald, Germany. It had an output power of 12.5 kW at a frequency of 30 kHz, or 8 to 10 kW at 60 kHz. It consists of a DC electric motor (left) driving the alternator (right) through a gearbox (center) which steps up the rotation speed.
Goldschmidt alternator
–
Rotor of Eilvese machine
36.
UNESCO
–
The United Nations Educational, Scientific and Cultural Organization is a specialized agency of the United Nations based in Paris. It is the heir of the League of Nations International Committee on Intellectual Cooperation, UNESCO has 195 member states and nine associate members. Most of its offices are cluster offices covering three or more countries, national and regional offices also exist. UNESCO pursues its objectives through five major programs, education, natural sciences, social/human sciences, culture and it is also a member of the United Nations Development Group. UNESCO and its mandate for international cooperation can be traced back to a League of Nations resolution on 21 September 1921, on 18 December 1925, the International Bureau of Education began work as a non-governmental organization in the service of international educational development. However, the work of predecessor organizations was largely interrupted by the onset of World War II. On 30 October 1943, the necessity for an organization was expressed in the Moscow Declaration, agreed upon by China, the United Kingdom, the United States. This was followed by the Dumbarton Oaks Conference proposals of 9 October 1944, a prominent figure in the initiative for UNESCO was Rab Butler, the Minister of Education for the United Kingdom. At the ECO/CONF, the Constitution of UNESCO was introduced and signed by 37 countries, the Preparatory Commission operated between 16 November 1945, and 4 November 1946—the date when UNESCOs Constitution came into force with the deposit of the twentieth ratification by a member state. The first General Conference took place between 19 November to 10 December 1946, and elected Dr. Julian Huxley to Director-General and this change in governance distinguished UNESCO from its predecessor, the CICI, in how member states would work together in the organizations fields of competence. In 1956, the Republic of South Africa withdrew from UNESCO claiming that some of the organizations publications amounted to interference in the racial problems. South Africa rejoined the organization in 1994 under the leadership of Nelson Mandela, UNESCOs early work in the field of education included the pilot project on fundamental education in the Marbial Valley, Haiti, started in 1947. This project was followed by missions to other countries, including, for example. In 1948, UNESCO recommended that Member States should make free primary education compulsory, in 1990, the World Conference on Education for All, in Jomtien, Thailand, launched a global movement to provide basic education for all children, youths and adults. Ten years later, the 2000 World Education Forum held in Dakar, Senegal, UNESCOs early activities in culture included, for example, the Nubia Campaign, launched in 1960. The purpose of the campaign was to move the Great Temple of Abu Simbel to keep it from being swamped by the Nile after construction of the Aswan Dam, during the 20-year campaign,22 monuments and architectural complexes were relocated. This was the first and largest in a series of campaigns including Mohenjo-daro, Fes, Kathmandu, Borobudur, the organizations work on heritage led to the adoption, in 1972, of the Convention concerning the Protection of the World Cultural and Natural Heritage. The World Heritage Committee was established in 1976 and the first sites inscribed on the World Heritage List in 1978, since then important legal instruments on cultural heritage and diversity have been adopted by UNESCO member states in 2003 and 2005
UNESCO
–
UNESCO offices in
Brasília
UNESCO
–
UNESCO
UNESCO
–
UNESCO Institute for Water Education in
Delft
UNESCO
–
The Garden of Peace, UNESCO headquarters, Paris. Donated by the Government of Japan, this garden was designed by American-Japanese sculptor artist Isamu Noguchi in 1958 and installed by Japanese gardener Toemon Sano.
37.
World Heritage Site
–
A World Heritage Site is a landmark which has been officially recognized by the United Nations, specifically by the United Nations Educational, Scientific and Cultural Organization. Sites are selected on the basis of having cultural, historical, scientific or some form of significance. UNESCO regards these sites as being important to the interests of humanity. The programme catalogues, names, and conserves sites of outstanding cultural or natural importance to the common culture, under certain conditions, listed sites can obtain funds from the World Heritage Fund. The program was founded with the Convention Concerning the Protection of the Worlds Cultural and Natural Heritage, since then,192 state parties have ratified the convention, making it one of the most adhered to international instruments. As of July 2016,1052 sites are listed,814 cultural,203 natural, in 1959, the governments of Egypt and Sudan requested UNESCO to assist their countries to protect and rescue the endangered monuments and sites. In 1960, the Director-General of UNESCO launched an appeal to the Member States for an International Campaign to Save the Monuments of Nubia, the campaign, which ended in 1980, was considered a success. The project cost $80 million, about $40 million of which was collected from 50 countries, the projects success led to other safeguarding campaigns, saving Venice and its lagoon in Italy, the ruins of Mohenjo-daro in Pakistan, and the Borobodur Temple Compounds in Indonesia. UNESCO then initiated, with the International Council on Monuments and Sites, the United States initiated the idea of cultural conservation with nature conservation. The International Union for Conservation of Nature developed similar proposals in 1968, the Convention came into force on 17 December 1975. As of June 2016, it has been ratified by 192 states, including 188 UN member states plus the Cook Islands, the Holy See, Niue, a country must first list its significant cultural and natural sites, the result is called the Tentative List. A country may not nominate sites that have not been first included on the Tentative List, next, it can place sites selected from that list into a Nomination File. The Nomination File is evaluated by the International Council on Monuments and Sites and these bodies then make their recommendations to the World Heritage Committee. There are ten selection criteria – a site must meet at least one of them to be included on the list, up to 2004, there were six criteria for cultural heritage and four criteria for natural heritage. In 2005, this was modified so there is now only one set of ten criteria. Nominated sites must be of outstanding value and meet at least one of the ten criteria. Thus, the Geneva Convention treaty promulgates, Article 53, PROTECTION OF CULTURAL OBJECTS AND OF PLACES OF WORSHIP. There are 1,052 World Heritage Sites located in 165 States Party, of these,814 are cultural,203 are natural and 35 are mixed properties
World Heritage Site
–
Site #252:
Taj Mahal, an example of cultural heritage site
World Heritage Site
–
Logo of the
United Nations Educational, Scientific and Cultural Organization (UNESCO)
World Heritage Committee
World Heritage Site
–
Site #156:
Serengeti National Park, an example of natural heritage site
World Heritage Site
–
Site #274:
Historic Sanctuary of Machu Picchu, an example of mixed heritage site
38.
Georg von Arco
–
Georg Wilhelm Alexander Hans Graf von Arco was a German physicist, radio pioneer, and one of the joint founders of the Society for Wireless Telegraphy which became the Telefunken company. He was an engineer and the director of Telefunken. He was crucial in the development of technology in Europe. Arco served for a time as an assistant to Adolf Slaby, until 1930, Arco was one of the two managing directors of the company. He participated in the development of high performance tube transmitters, together with his teacher, Slaby, he was considerably involved in the study and development of high-frequency engineering in Germany. He was a Monist and a pacifist, between 1921-22, he was a chairman of the German Monist Federation. Arco was born on the estate of his father, Count Alexander Karl von Arco, in Großgorschütz, afterwards he took up a military career, a family tradition. After three years with the military, however, he left to study engineering and electro-technology in the technical university in Charlottenburg, Berlin. There he became acquainted with Professor Adolf Slaby, who had participated in Guglielmo Marconis transmission experiments on the coast of the English Channel, here the first German antenna system for wireless telegraphy was established. On 27 August a radio transmission to the German naval base Kongsnaes,1.6 kilometers away, was successful, in 1928 a plaque was fixed over the door of the bell tower of the Church of the Redeemer to commemorate to this feat. On 7 October 1897, the first radio link from Schöneberg to Rangsdorf in Berlin was successful, in 1898, at the end of his studies, Arco went to work as an engineer at the Kabelwerk Oberspree plant of AEG. At first Arco was responsible as an engineer for testing various cable types. Patent disputes between Siemens and AEG resulted in companies, at the behest of William II, German Emperor, founding a common enterprise. The companys telegraph address, Telefunken, eventually became the company name, Arco greatly increased the power and range of early transmitters. Arcos greatest service lay in the development of the radio station at Nauen,20 miles west of Berlin. In 1909 he equipped it with a Löschfunksender, a quenched-spark transmitter, now contact could be made with the African colonies and naval vessels at sea. A decade later, in 1918, the power had increased tenfold. The station used a new technology introduced in 1912, a high frequency alternator with magnetic frequency multiplier converter
Georg von Arco
–
Georg von Arco (left) and August Karolus (de) (right) in 1928.
Georg von Arco
–
Plaque commemorating the first radio transmission in Germany, on the Church of the Redeemer in Sacrow/Potsdam.
39.
Guitar pickup
–
The signal from a pickup can also be recorded directly, using a DI box or broadcast on the radio or television. Most electric guitars and electric basses use magnetic pickups, acoustic guitars, upright basses and fiddles often use a piezoelectric pickup. A magnetic pickup consists of a permanent magnet with a core of such as alnico or ferrite. The pickup is most often mounted on the body of the instrument, Magnetic pickups used with string basses can be attached to the bridge. The permanent magnet creates a field, the motion of the vibrating steel strings disturbs the field, changing magnetic flux. The pickup is then connected with a cable to an amplifier which amplifies the signal to a sufficient magnitude of power to drive a loudspeaker. A pickup can also be connected to recording equipment via a patch cable, there may also be an internal preamplifier device mounted in an acoustic guitar or in an external box. When a preamp is used in way, it is between the pickup and cable and can significantly reduce the equivalent impedance of the pickup coil. The output voltage of magnetic pickups varies between 100 mV rms to over 1 V rms for some of the higher output types, some high-output pickups achieve this by employing very strong magnets, thus creating more flux and thereby more output. This can be detrimental to the sound because the magnets pull on the strings can cause problems with intonation as well as damp the strings. Other high-output pickups have more turns of wire to increase the voltage generated by the strings movement, however, this also increases the pickups output resistance/impedance, which can affect high frequencies if the pickup is not isolated by a buffer amplifier or a DI unit. The turns of wire in proximity to each other have an equivalent self-capacitance that and this resonance can accentuate certain frequencies, giving the pickup a characteristic tonal quality. The more turns of wire in the winding, the higher the output voltage, the inductive source impedance inherent in this type of transducer makes it less linear than other forms of pickups, such as piezo-electric or optical. The tonal quality produced by this nonlinearity is, however, subject to taste, the external load usually consists of resistance and capacitance between the hot lead and shield in the guitar cable. The electric cable also has a capacitance, which can be a significant portion of the overall system capacitance and this arrangement of passive components forms a resistively-damped second-order low-pass filter. Single coil pickups act like an antenna and are prone to pick up mains hum along with the musical signal. Mains hum consists of a signal at a nominal 50 or 60 Hz, depending on local alternating current frequency. The changing magnetic flux caused by the mains current links with the windings of the pickup, the pickups also are sensitive to the electromagnetic field from nearby cathode ray tubes in video monitors or televisions
Guitar pickup
–
Three magnetic pickups on a
Peavey Raptor with the pickup configuration of a
fat-strat (H-S-S). The bridge (right) pickup is a
humbucker and the neck (left) and middle pickups are
single coils.
Guitar pickup
–
Single coil pickups,
Fender Stratocaster (1963)
Guitar pickup
–
PRS 's Dragon humbucker
Guitar pickup
–
Split pole pickups, Fender Jazz Bass
40.
Magnetic field
–
A magnetic field is the magnetic effect of electric currents and magnetic materials. The magnetic field at any point is specified by both a direction and a magnitude, as such it is represented by a vector field. The term is used for two distinct but closely related fields denoted by the symbols B and H, where H is measured in units of amperes per meter in the SI, B is measured in teslas and newtons per meter per ampere in the SI. B is most commonly defined in terms of the Lorentz force it exerts on moving electric charges, Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. In quantum physics, the field is quantized and electromagnetic interactions result from the exchange of photons. Magnetic fields are used throughout modern technology, particularly in electrical engineering. The Earth produces its own field, which is important in navigation. Rotating magnetic fields are used in electric motors and generators. Magnetic forces give information about the carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits, noting that the resulting field lines crossed at two points he named those points poles in analogy to Earths poles. He also clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them, almost three centuries later, William Gilbert of Colchester replicated Petrus Peregrinus work and was the first to state explicitly that Earth is a magnet. Published in 1600, Gilberts work, De Magnete, helped to establish magnetism as a science, in 1750, John Michell stated that magnetic poles attract and repel in accordance with an inverse square law. Charles-Augustin de Coulomb experimentally verified this in 1785 and stated explicitly that the north and south poles cannot be separated, building on this force between poles, Siméon Denis Poisson created the first successful model of the magnetic field, which he presented in 1824. In this model, a magnetic H-field is produced by magnetic poles, three discoveries challenged this foundation of magnetism, though. First, in 1819, Hans Christian Ørsted discovered that an electric current generates a magnetic field encircling it, then in 1820, André-Marie Ampère showed that parallel wires having currents in the same direction attract one another. Finally, Jean-Baptiste Biot and Félix Savart discovered the Biot–Savart law in 1820, extending these experiments, Ampère published his own successful model of magnetism in 1825. This has the benefit of explaining why magnetic charge can not be isolated. Also in this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism, in 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field
Magnetic field
–
One of the first drawings of a magnetic field, by
René Descartes, 1644. It illustrated his theory that magnetism was caused by the circulation of tiny helical particles, "threaded parts", through threaded pores in magnets.
Magnetic field
–
Magnetic field of an ideal cylindrical
magnet with its axis of symmetry inside the image plane. The magnetic field is represented by
magnetic field lines, which show the direction of the field at different points.
Magnetic field
–
Hans Christian Ørsted, Der Geist in der Natur, 1854
41.
Direct current
–
Direct current is a flow of electrical charge carriers that always takes place in the same direction. The current need not always have the magnitude, but if it is to be defined as dc. This contrasts with alternating current which varies the direction of flow, sources of direct current include power supplies, electrochemical cells and batteries, and photovoltaic cells and panels. The intensity, or amplitude, of a direct current might fluctuate with time, in some such cases the dc has an ac component superimposed on it. An example of this is the output of a cell that receives a modulated light communications signal. A source of dc is sometimes called a dc generator, batteries and various other sources of dc produce a constant voltage. This is called pure dc and can be represented by a straight, the peak and effective values are the same. The peak to peak value is zero because the instantaneous amplitude never changes, in some instances the value of a dc voltage pulsates or oscillates rapidly with time, in a manner similar to the changes in an ac wave. The unfiltered output of a wave or a full wave rectifier. In 1820, Hans Christian Orsted discovered that electrical current creates a magnetic field and this discovery made scientists relate magnetism to the electric phenomena. In 1879, Thomas Edison invented the light bulb. He improved a 50-year-old idea using lower current electricity, a vacuum inside the globe and a small carbonized filament. At that time, the idea of lightning was not new. Edison not only invented an incandescent electric light, but an electric lighting system contained all the necessary elements to make the incandescent light safe, economical. Prior to 1879, direct current electricity had been used in lighting for the outdoors and it was in the 1880s when the modern electric utility industry began. It was an evolution from street lighting systems and from gas and it was located in Lower Manhattan, on Pearl Street. This station provided light and electricity to customers in a one square mile range, the station was called Thomas Edisons Pearl Street Electricity Generating Station. This station introduced four elements of an electric utility system, Efficient distribution, competitive price, reliable central generation
Direct current
–
Direct Current (red curve). The horizontal axis measures time; the vertical, current or voltage.
42.
Transformer
–
A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. A varying current in one coil of the transformer produces a magnetic field. Power can be transferred between the two coils through the field, without a metallic connection between the two circuits. Faradays law of induction discovered in 1831 described this effect, Transformers are used to increase or decrease the alternating voltages in electric power applications. A wide range of designs is encountered in electronic and electric power applications. Transformers range in size from RF transformers less than a centimeter in volume to units interconnecting the power grid weighing hundreds of tons. For simplification or approximation purposes, it is common to analyze the transformer as an ideal transformer model as presented in the two images. An ideal transformer is a theoretical, linear transformer that is lossless and perfectly coupled, perfect coupling implies infinitely high core magnetic permeability and winding inductances and zero net magnetomotive force. A varying current in the primary winding creates a varying magnetic flux in the transformer core. This varying magnetic field at the secondary winding induces a varying EMF or voltage in the secondary winding due to electromagnetic induction. The primary and secondary windings are wrapped around a core of high magnetic permeability so that all of the magnetic flux passes through both the primary and secondary windings. With a voltage source connected to the winding and load impedance connected to the secondary winding. The primary EMF is sometimes termed counter EMF and this is in accordance with Lenzs law, which states that induction of EMF always opposes development of any such change in magnetic field. The transformer winding voltage ratio is shown to be directly proportional to the winding turns ratio according to eq. common usage having evolved over time from turn ratio to turns ratio. However, some use the inverse definition. The ideal transformer model assumes that all flux generated by the primary winding links all the turns of winding, including itself. In practice, some flux traverses paths that take it outside the windings, Such flux is termed leakage flux, and results in leakage inductance in series with the mutually coupled transformer windings. Leakage flux results in energy being alternately stored in and discharged from the fields with each cycle of the power supply
Transformer
–
Pole-mounted
distribution transformer with
center-tapped secondary winding used to provide '
split-phase ' power for residential and light commercial service, which in North America is typically rated 120/240 V.
Transformer
–
Instrument transformer, with polarity dot and X1 markings on LV side terminal
Transformer
–
Real transformer equivalent circuit
Transformer
–
Core form = core type; shell form = shell type
43.
Telegraphy
–
Telegraphy is the long-distance transmission of textual or symbolic messages without the physical exchange of an object bearing the message. Thus semaphore is a method of telegraphy, whereas pigeon post is not, telegraphy requires that the method used for encoding the message be known to both sender and receiver. Such methods are designed according to the limits of the medium used. The use of signals, beacons, reflected light signals. In the 19th century, the harnessing of electricity led to the invention of electrical telegraphy, the advent of radio in the early 20th century brought about radiotelegraphy and other forms of wireless telegraphy. The word telegraph was first coined by the French inventor of the Semaphore line, Claude Chappe, a telegraph is a device for transmitting and receiving messages over long distances, i. e. for telegraphy. The word telegraph alone now generally refers to an electrical telegraph, Wireless telegraphy is also known as CW, for continuous wave, as opposed to the earlier radio technique of using a spark gap. Contrary to the definition used by Chappe, Morse argued that the term telegraph can strictly be applied only to systems that transmit. This is to be distinguished from semaphore, which transmits messages. Smoke signals, for instance, are to be considered semaphore, according to Morse, telegraph dates only from 1832 when Pavel Schilling invented one of the earliest electrical telegraphs. A telegraph message sent by a telegraph operator or telegrapher using Morse code was known as a telegram. A cablegram was a sent by a submarine telegraph cable. Later, a Telex was a sent by a Telex network. A wire picture or wire photo was a picture that was sent from a remote location by a facsimile telegraph. A diplomatic telegram, also known as a cable, is the term given to a confidential communication between a diplomatic mission and the foreign ministry of its parent country. These continue to be called telegrams or cables regardless of the used for transmission. Commercial electrical telegraphs were introduced from 1837, the first telegraphs came in the form of optical telegraph, including the use of smoke signals, beacons, or reflected light, which have existed since ancient times. Early proposals for a telegraph system were made to the Royal Society by Robert Hooke in 1684 and were first implemented on an experimental level by Sir Richard Lovell Edgeworth in 1767
Telegraphy
–
Replica of
Claude Chappe 's optical telegraph on the Litermont near
Nalbach, Germany
Telegraphy
–
Demonstration of the semaphore
Telegraphy
–
Pavel Schilling, an early pioneer of electrical telegraphy
Telegraphy
–
Cooke and Wheatstone's five-needle, six-wire telegraph
44.
Magnetic amplifier
–
The magnetic amplifier is an electromagnetic device for amplifying electrical signals. The magnetic amplifier was invented early in the 20th century, and was used as an alternative to tube amplifiers where robustness. World War II Germany perfected this type of amplifier, and it was used in the V-2 rocket, the magnetic amplifier was most prominent in power control and low-frequency signal applications from 1947 to about 1957, when the transistor began to supplant it. The magnetic amplifier has now largely superseded by the transistor-based amplifier, except in a few safety critical. Combinations of transistor and mag-amp techniques are still used, visually a mag amp device may resemble a transformer, but the operating principle is quite different from a transformer – essentially the mag amp is a saturable reactor. It makes use of saturation of the core, a non-linear property of a certain class of transformer cores. The typical magnetic amplifier consists of two separate but similar transformer magnetic cores, each of which has two windings, a control winding and an AC winding. A small DC current from a source is fed into the series-connected control windings. The AC windings may be connected either in series or in parallel, the amount of control current fed into the control winding sets the point in the AC winding waveform at which either core will saturate. A relatively small DC current on the winding is able to control or switch large AC currents on the AC windings. Two magnetic cores are used because the AC current will generate high voltage in the control windings, by connecting them in opposite phase, the two cancel each other, so that no current is induced in the control circuit. The magnetic amplifier is a device with no moving parts. It has no mechanism and has a good tolerance to mechanical shock. Multiple isolated signals may be summed by additional control windings on the magnetic cores, the windings of a magnetic amplifier have a higher tolerance to momentary overloads than comparable solid-state devices. The magnetic amplifier is used as a transducer in applications such as current measurement. The reactor cores of magnetic amplifiers withstand neutron radiation extremely well, for this special reason magnetic amplifiers have been used in nuclear power applications. The gain available from a stage is limited and low compared to electronic amplifiers. Solid-state electronic amplifiers can be compact and efficient than magnetic amplifiers
Magnetic amplifier
–
A saturable reactor, illustrating the principle of a magnetic amplifier
45.
Hertz (unit)
–
The hertz is the unit of frequency in the International System of Units and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide proof of the existence of electromagnetic waves. Hertz are commonly expressed in SI multiples kilohertz, megahertz, gigahertz, kilo means thousand, mega meaning million, giga meaning billion and tera for trillion. Some of the units most common uses are in the description of waves and musical tones, particularly those used in radio-. It is also used to describe the speeds at which computers, the hertz is equivalent to cycles per second, i. e. 1/second or s −1. In English, hertz is also used as the plural form, as an SI unit, Hz can be prefixed, commonly used multiples are kHz, MHz, GHz and THz. One hertz simply means one cycle per second,100 Hz means one hundred cycles per second, and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, the rate of aperiodic or stochastic events occur is expressed in reciprocal second or inverse second in general or, the specific case of radioactive decay, becquerels. Whereas 1 Hz is 1 cycle per second,1 Bq is 1 aperiodic radionuclide event per second, the conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second is ω =2 π f and f = ω2 π. This SI unit is named after Heinrich Hertz, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, the hertz is named after the German physicist Heinrich Hertz, who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission in 1930, the term cycles per second was largely replaced by hertz by the 1970s. One hobby magazine, Electronics Illustrated, declared their intention to stick with the traditional kc. Mc. etc. units, sound is a traveling longitudinal wave which is an oscillation of pressure. Humans perceive frequency of waves as pitch. Each musical note corresponds to a frequency which can be measured in hertz. An infants ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz, the range of ultrasound, infrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtoHz into the terahertz range and beyond. Electromagnetic radiation is described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz. Radio frequency radiation is measured in kilohertz, megahertz, or gigahertz
Hertz (unit)
–
Details of a
heartbeat as an example of a non-
sinusoidal periodic phenomenon that can be described in terms of hertz. Two complete cycles are illustrated.
Hertz (unit)
–
A
sine wave with varying frequency
46.
Very low frequency
–
Very low frequency or VLF is the ITU designation for radio frequencies in the range of 3 kHz to 30 kHz and corresponding wavelengths from 100 to 10 kilometres, respectively. The band is known as the myriametre band or myriametre wave as the wavelengths range from one to ten myriametres. Due to its bandwidth, audio transmission is highly impractical in this band. The VLF band is used for a few radio navigation services, government time radio stations, since VLF waves can penetrate at least 40 meters into saltwater, they are used for military communication with submarines. The main mode of long distance propagation is an Earth-ionosphere waveguide mechanism, the Earth is surrounded by a conductive layer of electrons and ions in the upper atmosphere, the ionosphere D layer at 60 km altitude, which reflects VLF radio waves. The conductive ionosphere and the conductive Earth, form a horizontal duct a few VLF wavelengths high, the waves travel in a zigzag path around the Earth, reflected alternately by the Earth and the ionosphere, in TM mode. Therefore, VLF transmissions are very stable and reliable, and are used for distance communication. Propagation distances of 5000 to 20000 km have been realized, however, atmospheric noise is high in the band, including such phenomena as whistlers, caused by lightning. VLF waves can penetrate seawater to a depth of at least 10 to 40 meters, depending on the frequency employed, VLF waves at certain frequencies have been found to cause electron precipitation. A major practical drawback to this band is that because of the length of the waves, vertical antennas must be used because VLF waves propagate in vertical polarization, but a quarter-wave vertical antenna at 30 kHz would be 2.5 kilometers high. So practical transmitting antennas are short, a small fraction of a wavelength long. Due to their low radiation resistance they are inefficient, radiating only 10% to 50% of the power at most. With the rest of the power dissipated in the antenna/ground system resistances, Very high power transmitters are required to radiate enough power for long distance communication. Transmitting antennas for VLF frequencies are very large antennas, up to a mile across. They consist of a series of radio masts, linked at the top with a network of cables. Either the towers themselves or vertical wires serve as monopole radiators, high power stations use variations on the umbrella antenna such as the delta and trideco antennas, or multiply-tuned flattop antennas. For low power transmitters, inverted-L and T antennas are used, a large loading coil is required at the antenna feed point to cancel the capacitive reactance of the antenna to make it resonant. To minimize power dissipated in the ground, these antennas require extremely low resistance ground systems, the high capacitance and inductance and low resistance of the antenna-loading coil combination, makes it act electrically like a high Q tuned circuit
Very low frequency
–
A VLF receiving antenna at
Palmer Station, Antarctica, operated by
Stanford University.
Very low frequency
–
Part of the
aerial of the
Grimeton VLF transmitter
47.
Tuned circuit
–
The circuit can act as an electrical resonator, an electrical analogue of a tuning fork, storing energy oscillating at the circuits resonant frequency. LC circuits are used either for generating signals at a particular frequency and they are key components in many electronic devices, particularly radio equipment, used in circuits such as oscillators, filters, tuners and frequency mixers. An LC circuit is a model since it assumes there is no dissipation of energy due to resistance. Any practical implementation of an LC circuit will always include loss resulting from small but non-zero resistance within the components, the purpose of an LC circuit is usually to oscillate with minimal damping, so the resistance is made as low as possible. While no practical circuit is without losses, it is instructive to study this ideal form of the circuit to gain understanding. For a circuit model incorporating resistance, see RLC circuit, the two-element LC circuit described above is the simplest type of inductor-capacitor network. It is also referred to as a second order LC circuit to distinguish it more complicated LC networks with more inductors and capacitors. Such LC networks with more than two reactances may have more than one resonant frequency, the order of the network is the order of the rational function describing the network in the complex frequency variable s. Generally, the order is equal to the number of L and C elements in the circuit, an LC circuit, oscillating at its natural resonant frequency, can store electrical energy. A capacitor stores energy in the field between its plates, depending on the voltage across it, and an inductor stores energy in its magnetic field. If an inductor is connected across a capacitor, current will start to flow through the inductor, building up a magnetic field around it. Eventually all the charge on the capacitor will be gone and the voltage across it will reach zero, however, the current will continue, because inductors resist changes in current. The current will begin to charge the capacitor with a voltage of opposite polarity to its original charge. Due to Faradays law, the EMF which drives the current is caused by a decrease in the magnetic field, when the magnetic field is completely dissipated the current will stop and the charge will again be stored in the capacitor, with the opposite polarity as before. Then the cycle will begin again, with the current flowing in the direction through the inductor. The charge flows back and forth between the plates of the capacitor, through the inductor, the energy oscillates back and forth between the capacitor and the inductor until internal resistance makes the oscillations die out. In most applications the tuned circuit is part of a circuit which applies alternating current to it. If the frequency of the current is the circuits natural resonant frequency
Tuned circuit
–
LC circuit (left) consisting of ferrite coil and capacitor used as a tuned circuit in a receiver in a
radio clock.
Tuned circuit
–
LC circuit diagram
48.
Resonant frequency
–
In physics, resonance is a phenomenon in which a vibrating system or external force drives another system to oscillate with greater amplitude at a specific preferential frequency. Frequencies at which the amplitude is a relative maximum are known as the systems resonant frequencies or resonance frequencies. At resonant frequencies, small periodic driving forces have the ability to produce large amplitude oscillations, Resonance occurs when a system is able to store and easily transfer energy between two or more different storage modes. However, there are some losses from cycle to cycle, called damping, when damping is small, the resonant frequency is approximately equal to the natural frequency of the system, which is a frequency of unforced vibrations. Some systems have multiple, distinct, resonant frequencies, resonant systems can be used to generate vibrations of a specific frequency, or pick out specific frequencies from a complex vibration containing many frequencies. Resonance occurs widely in nature, and is exploited in many manmade devices and it is the mechanism by which virtually all sine waves and vibrations are generated. Many sounds we hear, such as when hard objects of metal, glass, light and other short wavelength electromagnetic radiation is produced by resonance on an atomic scale, such as electrons in atoms. A familiar example is a swing, which acts as a pendulum. Pushing a person in a swing in time with the interval of the swing makes the swing go higher and higher. This is because the energy the swing absorbs is maximized when the match the swings natural oscillations. It may cause violent swaying motions and even catastrophic failure in improperly constructed structures including bridges, buildings, trains, avoiding resonance disasters is a major concern in every building, tower, and bridge construction project. As a countermeasure, shock mounts can be installed to absorb resonant frequencies, the Taipei 101 building relies on a 660-tonne pendulum —a tuned mass damper—to cancel resonance. Furthermore, the structure is designed to resonate at a frequency that does not typically occur, buildings in seismic zones are often constructed to take into account the oscillating frequencies of expected ground motion. Clocks keep time by mechanical resonance in a wheel, pendulum. The cadence of runners has been hypothesized to be energetically favorable due to resonance between the energy stored in the lower limb and the mass of the runner. Acoustic resonance is a branch of mechanical resonance that is concerned with the mechanical vibrations across the range of human hearing. Like mechanical resonance, acoustic resonance can result in failure of the object at resonance. The classic example of this is breaking a glass with sound at the precise resonant frequency of the glass
Resonant frequency
–
Pushing a person in a
swing is a common example of resonance. The loaded swing, a
pendulum, has a
natural frequency of oscillation, its resonant frequency, and resists being pushed at a faster or slower rate.
Resonant frequency
–
Increase of amplitude as damping decreases and frequency approaches resonant frequency of a driven
damped simple harmonic oscillator.
Resonant frequency
–
NMR Magnet at HWB-NMR, Birmingham, UK. In its strong 21.2-
tesla field, the proton resonance is at 900 MHz.
49.
Arc converter
–
The arc converter used an electric arc to convert direct current electricity into radio frequency alternating current. It was used as a transmitter from 1903 until the 1920s when it was replaced by vacuum tube transmitters. One of the first transmitters that could generate continuous sinusoidal waves and it is on the list of IEEE Milestones as a historic achievement in electrical engineering. Elihu Thomson discovered that a carbon arc shunted with a tuned circuit would sing. This singing arc was probably limited to audio frequencies, Bureau of Standards credits William Duddell with the shunt resonant circuit around 1900. The English engineer William Duddell discovered how to make a resonant circuit using an arc lamp. Duddells musical arc operated at frequencies, and Duddell himself concluded that it was impossible to make the arc oscillate at radio frequencies. Valdemar Poulsen, who had demonstrated the Telegraphone at the Paris Exhibition of 1900, poulsens arc could generate frequencies of up to 200 kilohertz and was patented in 1903. After a few years of development the arc technology was transferred to Germany and Great Britain in 1906 by Poulsen, his collaborator Peder Oluf Pedersen, in 1909 the American patents as well as a few arc converters were bought by Cyril F. Elwell. Later the US Navy also adopted the Poulsen system, only the arc converter with passive frequency conversion was suitable for portable and maritime use. This made it the most important mobile radio system for about a decade until it was superseded by vacuum tube systems, in 1922, the Bureau of Standards stated, the arc is the most widely used transmitting apparatus for high-power, long-distance work. It is estimated that the arc is now responsible for 80 per cent of all the energy actually radiated into space for radio purposes during a given time, unlike the existing radio transmitter of the time, the spark-gap transmitter, the arc converter produces undamped or continuous waves. This was an important feature as the use of damped waves resulted in lower efficiency and communications effectiveness. This more refined method for generating continuous-wave radio signals was initially developed by Danish inventor Valdemar Poulsen, there are three cases for an arc oscillator. In the first case, the AC current in the condenser i0 is much smaller than the DC supply current i1, the Duddell arc is an example of the first case, but the first case is not practical for RF transmitters. In the second case, the condenser AC discharge current is enough to extinguish the arc. This second case is the Poulsen arc, in the third case, the arc extinguishes but may reignite when the condenser current reverses. The third case is a spark gap and produces damped oscillations
Arc converter
–
1 megawatt Poulsen arc transmitter used by the U.S. Navy around 1918 in shore radio stations to communicate with its fleet worldwide, one of the largest arc transmitters ever built.
Arc converter
–
Poulsen's first arc converter, from 1903
50.
Spark-gap transmitter
–
A spark-gap transmitter is a device that generates radio frequency electromagnetic waves using a spark gap. Spark gap transmitters were the first devices to demonstrate practical radio transmission, later, more efficient transmitters were developed based on rotary machines like the high-speed Alexanderson alternators and the static Poulsen Arc generators. Even when vacuum tube based transmitters had been installed, many retained their crude. However, by 1940, the technology was no longer used for communication, use of the spark-gap transmitter led to many radio operators being nicknamed Sparks long after they ceased using spark transmitters. Even today, the German verb funken, literally, to spark, the effects of sparks causing unexplained action at a distance, such as inducing sparks in nearby devices, had been noticed by scientists and experimenters well before the invention of radio. Extensive experiments were conducted by Joseph Henry, Thomas Edison and David Edward Hughes, with no other theory to explain the phenomenon, it was usually written off as electromagnetic induction. Hertz used a spark gap transmitter and a tuned spark gap detector located a few meters from the source. Many experimenters used the spark gap setup to further investigate the new Hertzian wave phenomenon, including Oliver Lodge, the Italian inventor Guglielmo Marconi used a spark-gap transmitter in his experiments to develop the radio phenomenon into a wireless telegraphy system in the early 1890s. In 1895 he succeeded in transmitting over a distance of 1 1/4 miles and his first transmitter consisted of an induction coil connected between a wire antenna and ground, with a spark gap across it. Every time the induction coil pulsed, the antenna was momentarily charged up to tens of thousands of volts until the gap started to arc. This acted as a switch, essentially connecting the antenna to ground. While the various systems of spark transmitters worked well enough to prove the concept of wireless telegraphy. The biggest problem was that the power that could be transmitted was directly determined by how much electrical charge the antenna could hold. Because the capacitance of practical antennas is quite small, the way to get a reasonable power output was to charge it up to very high voltages. However, this made transmission impossible in rainy or even damp conditions, also, it necessitated a quite wide spark gap, with a very high electrical resistance, with the result that most of the electrical energy was used simply to heat up the air in the spark gap. Another problem with the transmitter was a result of the shape of the waveform produced by each burst of electromagnetic radiation. These transmitters radiated an extremely dirty wide band signal that could interfere with transmissions on nearby frequencies. Receiving sets relatively close to such a transmitter had entire sections of a band masked by this wide band noise, reginald Fessendens first attempts to transmit voice employed a spark transmitter operating at approximately 10,000 sparks/second
Spark-gap transmitter
–
Pictorial diagram of a simple spark-gap transmitter showing examples of the early electronic components used. From a 1917 boy's book, it is typical of the low power transmitters homebuilt by thousands of amateurs to explore the exciting new technology of radio.
