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  1. Transformer - Wikipedia › wiki › Transformer

    Thin laminations are generally used on high-frequency transformers, with some of very thin steel laminations able to operate up to 10 kHz. Laminating the core greatly reduces eddy-current losses One common design of laminated core is made from interleaved stacks of E-shaped steel sheets capped with I-shaped pieces, leading to its name of 'E-I ...

  2. Very high frequency — Wikipedia Republished // WIKI 2 › en › Very_high_frequency
    • Propagation Characteristics
    • Line-Of-Sight Calculation
    • Antennas
    • Universal Use
    • by Country
    • Unlicensed Operation
    • See Also

    Radio waves in the VHF band prop­a­gate mainly by line-of-sight and ground-bounce paths; un­like in the HF band there is only some re­flec­tion at lower fre­quen­cies from the ionos­phere (sky­wave prop­a­ga­tion). They do not fol­low the con­tour of the Earth as ground waves and so are blocked by hills and moun­tains, al­though be­cause they are weakly re­fracted (bent) by the at­mos­phere they can travel some­what be­yond the vi­sual hori­zon out to about 160 km (100 miles). They can pen­e­trate build­ing walls and be re­ceived in­doors, al­though in urban areas re­flec­tions from build­ings cause mul­ti­path prop­a­ga­tion, which can in­ter­fere with tele­vi­sion re­cep­tion. At­mos­pheric radio noise and in­ter­fer­ence (RFI) from elec­tri­cal equip­ment is less of a prob­lem in this and higher fre­quency bands than at lower fre­quen­cies. The VHF band is the first band at which ef­fi­cient trans­mit­ting an­ten­nas are small enough that they can be mounted on ve­hi­cles and por...

    For ana­log TV, VHF trans­mis­sion range is a func­tion of trans­mit­ter power, re­ceiver sen­si­tiv­ity, and dis­tance to the hori­zon, since VHF sig­nals prop­a­gate under nor­mal con­di­tions as a near line-of-sight phe­nom­e­non. The dis­tance to the radio hori­zonis slightly ex­tended over the geo­met­ric line of sight to the hori­zon, as radio waves are weakly bent back to­ward the Earth by the at­mos­phere. An ap­prox­i­ma­tion to cal­cu­late the line-of-sight hori­zon dis­tance (on Earth) is: 1. distance in nautical miles = 1.23×Af{\\displaystyle 1.23\\times {\\sqrt {A_{f}}}} where Af{\\displaystyle A_{f}} is the height of the antenna in feet[citation needed] 2. distance in kilometers = 12.746×Am{\\displaystyle {\\sqrt {12.746\\times A_{m}}}} where Am{\\displaystyle A_{m}} is the height of the antenna in meters.[citation needed] These ap­prox­i­ma­tions are only valid for an­ten­nas at heights that are small com­pared to the ra­dius of the Earth. They may not nec­es­sar­ily be ac­cu...

    VHF is the first band at which wave­lengths are small enough that ef­fi­cient trans­mit­ting an­ten­nas are short enough to mount on ve­hi­cles and hand­held de­vices, a quar­ter wave whip an­tenna at VHF fre­quen­cies is 25 cm to 2.5 meter (10 inches to 8 feet) long. So the VHF and UHF wave­lengths are used for two-way ra­dios in ve­hi­cles, air­craft, and hand­held trans­ceivers and walkie-talkies. Portable ra­dios usu­ally use whips or rub­ber ducky an­ten­nas, while base sta­tions usu­ally use larger fiber­glass whips or collinear ar­raysof ver­ti­cal dipoles. For di­rec­tional an­ten­nas, the Yagi an­tenna is the most widely used as a high gain or "beam" an­tenna. For tele­vi­sion re­cep­tion, the Yagi is used, as well as the log-pe­ri­odic an­tenna due to its wider band­width. He­li­cal and turn­stile an­ten­nas are used for satel­lite com­mu­ni­ca­tion since they em­ploy cir­cu­lar po­lar­iza­tion. For even higher gain, mul­ti­ple Yagis or he­li­cals can be mounted to­gether...

    Cer­tain sub­parts of the VHF band have the same use around the world. Some na­tional uses are de­tailed below. 1. 50–54 MHz: Amateur Radio 6-meter band. 2. 108–118 MHz: Air navigation beacons VOR and Instrument Landing Systemlocalizer. 3. 118–137 MHz: Airband for air traffic control, AM, 121.5 MHz is emergency frequency 4. 144–146 MHz: Amateur Radio 2-meter band(Extends up to 148 MHz in some Regions).


    The VHF TV band in Aus­tralia was orig­i­nally al­lo­cated chan­nels 1 to 10-with chan­nels 2, 7 and 9 as­signed for the ini­tial ser­vices in Syd­ney and Mel­bourne, and later the same chan­nels were as­signed in Bris­bane, Ade­laide and Perth. Other cap­i­tal cities and re­gional areas used a com­bi­na­tion of these and other fre­quen­cies as avail­able. The ini­tial com­mer­cial ser­vices in Ho­bart and Dar­win were re­spec­tively al­lo­cated chan­nels 6 and 8 rather than 7 or 9. By the ea...

    New Zealand

    1. 44–51, 54–68 MHz: Band ITelevision (channels 1–3) 2. 87.5–108 MHz: Band IIRadio 3. 174–230 MHz: Band IIITelevision (channels 4–11) Until 2013, the four main Free-to-Air TV sta­tions in New Zealand used the VHF Tele­vi­sion bands (Band I and Band III) to trans­mit to New Zealand house­holds. Other sta­tions, in­clud­ing a va­ri­ety of pay and re­gional free-to-air sta­tions, were forced to broad­cast in the UHFband, since the VHF band had been very over­loaded with four sta­tions shar­ing a...

    United Kingdom

    British tele­vi­sion orig­i­nally used VHF band I and band III. Tele­vi­sion on VHF was in black and white with 405-line for­mat (al­though there were ex­per­i­ments with all three colour systems-NTSC, PAL, and SECAM-adapted for the 405-line sys­tem in the late 1950s and early 60s). British colour tele­vi­sion was broad­cast on UHF (chan­nels 21-69), be­gin­ning in the late 1960s. From then on, TV was broad­cast on both VHF and UHF (VHF being a mono­chro­matic down­con­ver­sion from the 625-l...

    In some coun­tries, par­tic­u­larly the United States and Canada, lim­ited low-power li­cense-free op­er­a­tion is avail­able in the FM broad­cast band for pur­poses such as mi­cro-broad­cast­ing and send­ing out­put from CDor dig­i­tal media play­ers to ra­dios with­out aux­il­iary-in jacks, though this is il­le­gal in some other coun­tries. This prac­tice was le­galised in the United King­dom on 8 De­cem­ber 2006.

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  4. Very high frequency - Wikipedia › wiki › VHF_II

    Very high frequency ( VHF) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF).

    • 10 to 1 m
    • 30 MHz to 300 MHz
  5. High frequency - Wikipedia › wiki › High_frequency

    High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one hundred meters).

    • 100 to 10 m
    • 3 to 30 MHz
  6. Transformer types - Wikipedia › wiki › Transformer_types

    A Flyback transformer is a high-voltage, high-frequency transformer used in plasma balls and with cathode-ray tubes (CRTs). It provides the high (often several kV) anode DC voltage required for operation of CRTs. Variations in anode voltage supplied by the flyback can result in distortions in the image displayed by the CRT.

  7. Variable-frequency transformer - Wikipedia › wiki › Variable-frequency_transformer

    A variable-frequency transformer is used to transmit electricity between two alternating current frequency domains. The VFT is a relatively recent development. Most asynchronous grid inter-ties use high-voltage direct current converters, while synchronous grid inter-ties are connected by lines and "ordinary" transformers, but without the ability to control power flow between the systems. It can be thought of as a very high power synchro, or a rotary converter acting as a frequency changer, which

  8. Transformer | Wikitronics | Fandom › wiki › Transformer
    • History
    • Basic Principles
    • Practical Considerations
    • Transformer Types and Uses
    • Construction
    • External Links

    Michael Faraday built the first transformer in 1831, although he used it only to demonstrate the principle of electromagnetic induction and did not foresee its practical uses. Lucien Gaulard and John Dixon Gibbs, who first exhibited a device called a 'secondary generator' in London in 1882 and then sold the idea to American company Westinghouse. This may have been the first practical power transformer. They also exhibited the invention in Turin in 1884, where it was adopted for an electric lighting system. Their early devices used an open iron core, which was soon abandoned in favour of a more efficient circular core with a closed magnetic path. Russian engineer Pavel Yablochkov in 1876 invented a lighting system based on a set of induction coils, where primary windings were connected to a source of alternating current and secondary windings could be connected to several "electric candles". As the patent said, such a system "allows to provide separate supply to several lighting fixt...

    Coupling by mutual induction

    The principles of the transformer are illustrated by consideration of a hypothetical ideal transformer consisting of two windings of zero resistance around a core of negligible reluctance. A voltage applied to the primary winding causes a current, which develops a magnetomotive force (MMF) in the core. The current required to create the MMF is termed the magnetising current; in the ideal transformer it is considered to be negligible. The MMF drives flux around the magnetic circuitof the core....

    Under load

    If a load impedance is connected to the secondary winding, a current will flow in the secondary circuit so created. The current develops an MMF over the secondary winding in opposition to that of the primary winding, so acting to cancel the flux in the core. The now decreased flux reduces the primary EMF, causing current in the primary circuit to increase to exactly offset the effect of the secondary MMF, and returning the flux to its former value. The core flux thus remains the same regardle...

    Circuit symbols

    Standard symbols

    Effect of frequency

    The time-derivative term in Faraday's Law implies that the flux in the core is the integral of the applied voltage. An ideal transformer would, at least hypothetically, work under direct-current excitation, with the core flux increasing linearly with time. In practice, the flux would rise very rapidly to the point where magnetic saturationof the core occurred and the transformer would cease to function as such. All practical transformers must therefore operate under alternating (or pulsed) cu...

    Energy losses

    An ideal transformer would have no energy losses, and would therefore be 100% efficient. Despite the transformer being amongst the most efficient of electrical machines, with experimental models using superconducting windings achieving efficiencies of 99.85%, energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 95%.A small transformer such as a plug-in...

    A variety of specialised transformer designs has been created to fulfil certain engineering applications. The numerous applications to which transformers are adapted lead them to be classified in many ways: 1. By power level: from a fraction of a volt-ampere(VA) to over a thousand MVA; 2. By frequency range: power-, audio- or radio frequency; 3. By voltage class: from a few volts to hundreds of kilovolts; 4. By cooling type: air cooled, oil filled, fan cooled, or water cooled; 5. By application function: such as power supply, impedance matching or circuit isolation; 6. By end purpose: distribution, rectifier, arc furnace, amplifier output; 7. By winding turns ratio: step-up, step-down, isolating (near equal ratio), variable.


    The wire of the adjacent turns in a coil, and in the different windings, must be electrically insulated from each other. The wire used is generally magnet wire. Magnet wire is a copper wire with a coating of varnish or some other synthetic coating. Transformers for years have used Formvarwire, which is a varnished type of magnet wire. The conducting material used for the winding depends upon the application. Small power and signal transformers are wound with solid copper wire, insulated usual...

    Winding insulation

    The turns of the windings must be insulated from each other to ensure that the current travels through the entire winding. The potential difference between adjacent turns is usually small, so that enamel insulation may suffice for small power transformers. Supplemental sheet or tape insulation is usually employed between winding layers in larger transformers. The transformer may also be immersed in transformer oil that provides further insulation. Although the oil is primarily used to cool th...


    Where transformers are intended for minimum electrostatic coupling between primary and secondary circuits, an electrostatic shield can be placed between windings to reduce the capacitance between primary and secondary windings. The shield may be a single layer of metal foil, insulated where it overlaps to prevent it acting as a shorted turn, or a single layer winding between primary and secondary. The shield is connected to earth ground. Transformers may also be enclosed by magnetic shields,...

    Inside Transformersfrom Denver University
    Understanding Transformers: Characteristics and Limitationsfrom Conformity Magazine
    DMOZ: Business: Electronics and Electrical: Substation and TransmissionTransformers for the Utility sector
  9. Transformer | Engineering | Fandom › wiki › Transformer
    • Basic Principles
    • Invention
    • Construction
    • Transformer Designs
    • Uses of Transformers
    • See Also

    Flux coupling

    A simple single phase transformer consists of two electrical conductors called the primary winding and the secondary winding. The primary is fed with a varying (alternating or pulsed continuous) electric current which creates a varying magnetic field around the conductor. According to the principle of mutual inductance, the secondary, which is placed in this varying magnetic field, will develop an electromotive force or EMF. If the ends of the secondary are connected together to form an elect...

    Electrical laws

    Consider the following two laws: 1. According to the law of conservation of energy, the powerdelivered by a transformer cannot exceed the power fed into it. 2. The power dissipated in a load at any instant is equal to the product of the voltage across it and the (in phase) current passing through it (see also Ohm's law). It follows from the above two laws that a transformer is not an amplifier. If the transformer is used to change power from one voltage to another, the magnitudes of the curre...

    Those credited with the invention of the transformer include: 1. Michael Faraday, who invented an 'induction ring' on August 29, 1831. This was the first transformer, although Faraday used it only to demonstrate the principle of electromagnetic inductionand did not foresee the use to which it would eventually be put. 2. Lucien Gaulard and John Dixon Gibbs, who first exhibited a device called a 'secondary generator' in London in 1881 and then sold the idea to American company Westinghouse. This may have been the first practical power transformer, but was not the first transformer of any kind. They also exhibited the invention in Turinin 1884, where it was adopted for an electric lighting system. Their early devices used a linear iron core, which was later abandoned in favour of a more efficient circular core. 3. William Stanley, an engineer for Westinghouse, who built the first practical device in 1885 after George Westinghouse bought Gaulard and Gibbs' patents. The core was made fro...

    A transformer usually has: 1. two or more insulated windings, to carry current 2. a core, in which the mutual magnetic field couplesthe windings. In transformers designed to operate at low frequencies, the windings are usually formed around an iron or steel core. This helps to confine the magnetic field within the transformer and increase its efficiency, although the presence of the core causes energy losses. Transformers made to operate at high frequencies may use other lower loss materials, or may use an air core. Power transformers are further classified by the exact arrangement of the core and windings as "shell type", "core type" and also by the number of "limbs" that carry the flux (3, 4 or 5 for a 3-phase transformer). The differences in the performance of each of these types, while of continuing interest to specialists, is perhaps more detail than is appropriate for a general encyclopedia.


    An autotransformerhas only a single winding, which is tapped at some point along the winding. AC or pulsed DC power is applied across a portion of the winding, and a higher (or lower) voltage is produced across another portion of the same winding. Autotransformers are used to compensate for voltage drop in a distribution system or for matching two transmission voltages, for example 115 kV and 138 kV. For voltage ratios not exceeding about 3:1, an autotransformer is less costly, lighter, small...

    Polyphase transformers

    For three-phase power, three separate single-phase transformers can be used, or all three phases can be connected to a single polyphase transformer. The three primary windings are connected together and the three secondary windings are connected together. The most common connections are Y-Δ, Δ-Y, Δ-Δ and Y-Y. If a winding is connected to earth (grounded) the earth connection point is usually the center point of a Y winding. There are many possible configurations that may involve more or fewer...

    Resonant transformers

    A resonant transformer is one that operates at the resonant frequency of one or more of its coils. The resonant coil, usually the secondary, acts as an inductor, and is connected in series with a capacitor. If the primary coil is driven by a periodic source of alternating current, such as a square or sawtooth wave, each pulse of current helps to build up an oscillation in the secondary coil. Due to resonance, a very high voltage can develop across the secondary, until it is limited by some pr...

    Electric power transmission over long distances. The simplicity, reliability, and economy of conversion of voltages by stationary transformers was the principal factor in the selection of alternati...
    High-voltage direct-current HVDCpower transmission systems
    Large, specially constructed power transformers are used for electric arc furnaces used in steelmaking.
    Rotating transformers are designed so that one winding turns while the other remains stationary. A common use was the video head system as used in VHS and Beta video tape players. These can pass po...

    Template:Wikibookspar 1. Main : Distributed generation, Electronic power supply, Electronics, Inductor, Pickup, Electrical network, Electricity distribution, Wet transformer, Electronics topics 2. Circuits: Ballast, Clamp meter, Repeating coil, Inverter (electrical), Ignition system, Electricity generation, Linear variable differential transformer, Neon signage, Regulator, Electrical substation, Switched-mode power supply, Technological applications of superconductivity, Tesla coil, Transducer 3. Electromagnetism: Alternating current, Electric power, Electric power transmission, Electromagnetic induction, Equivalent series resistance, High-voltage direct current, Impedance matching, Inductive coupling, Potential difference, Skin effect, Leakage inductance, Superconductivity 4. People: Ottó Bláthy, Miksa Déri, John Ambrose Fleming, Otto A. Knopp, William Stanley, Nikola Tesla, Milan Vidmar, George Westinghouse, Károly Zipernowsky 5. Other: DI unit, Polychlorinated biphenyl, Stafford,...

  10. High frequency — Wikipedia Republished // WIKI 2 › en › High_frequency
    • Propagation Characteristics
    • Uses
    • Antennas
    • See Also
    • Further Reading
    • External Links

    The dom­i­nant means of long-dis­tance com­mu­ni­ca­tion in this band is sky­wave ("skip") prop­a­ga­tion, in which radio waves di­rected at an angle into the sky re­fract back to Earth from lay­ers of ion­ized atoms in the ionos­phere.By this method HF radio waves can travel be­yond the hori­zon, around the curve of the Earth, and can be re­ceived at in­ter­con­ti­nen­tal dis­tances. How­ever, suit­abil­ity of this por­tion of the spec­trum for such com­mu­ni­ca­tion varies greatly with a com­plex com­bi­na­tion of fac­tors: 1. Sunlight/darkness at site of transmission and reception 2. Transmitter/receiver proximity to solar terminator 3. Season 4. Sunspot cycle 5. Solar activity 6. Polar aurora At any point in time, for a given "skip" com­mu­ni­ca­tion path be­tween two points, the fre­quen­cies at which com­mu­ni­ca­tion is pos­si­ble are spec­i­fied by these pa­ra­me­ters 1. Maximum usable frequency(MUF) 2. Lowest usable high frequency(LUF) and a 3. Frequency of optimum transmis...

    The main users of the high fre­quency spec­trum are: 1. Military and governmental communication systems 2. Aviation air-to-ground communications 3. Amateur radio 4. Shortwaveinternational and regional broadcasting 5. Maritime sea-to-shore and ship-to-ship services 6. Over-the-horizon radarsystems 7. Global Maritime Distress and Safety System(GMDSS) communication 8. Citizen's Band Radio services worldwide (generally 26-28 MHz, the higher portion of the HF band, that behaves more like low-VHF) The high fre­quency band is very pop­u­lar with am­a­teur radio op­er­a­tors, who can take ad­van­tage of di­rect, long-dis­tance (often in­ter-con­ti­nen­tal) com­mu­ni­ca­tions and the "thrill fac­tor" re­sult­ing from mak­ing con­tacts in vari­able con­di­tions. In­ter­na­tional short­wave broad­cast­ing uti­lizes this set of fre­quen­cies, as well as a seem­ingly de­clin­ing num­ber of "util­ity" users (ma­rine, avi­a­tion, mil­i­tary, and diplo­matic in­ter­ests), who have, in re­cent years...

    The most com­mon an­ten­nas in this band are wire an­ten­nas such as wire dipoles and the rhom­bic an­tenna; in the upper fre­quen­cies, mul­ti­ele­ment di­pole an­ten­nas such as the Yagi, quad, and log-pe­ri­odic an­ten­nas. Pow­er­ful short­wave broad­cast­ing sta­tions often use large wire cur­tain ar­rays. An­ten­nas for trans­mit­ting sky­waves are typ­i­cally made from hor­i­zon­tal dipoles or bot­tom-fed loops, both of which emit hor­i­zon­tally po­lar­ized waves. The pref­er­ence for hor­i­zon­tally po­lar­ized trans­mis­sion is be­cause (ap­prox­i­mately) only half of the sig­nal power trans­mit­ted by an an­tenna trav­els di­rectly into the sky; about half trav­els down­ward to­wards the ground and must "bounce" into the sky. For fre­quen­cies in the upper HF band, the ground is a bet­ter re­flec­tor of hor­i­zon­tally po­lar­ized waves, and bet­ter ab­sorber of power from ver­ti­cally po­lar­izedwaves. The ef­fect di­min­ishes for longer wave­lengths. For re­ceiv­ing, ra...

    Maslin, N.M. "HF Communications - A Systems Approach". ISBN 0-273-02675-5, Taylor & Francis Ltd, 1987
    Johnson, E.E., et al., "Advanced High-Frequency Radio Communications". ISBN 0-89006-815-1, Artech House, 1997
    Narayanamurti, V.; Störmer, H. L.; Chin, M. A.; Gossard, A. C.; Wiegmann, W. (1979-12-31). "Selective Transmission of High-Frequency Phonons by a Superlattice: The "Dielectric" Phonon Filter". Phys...
    Bejjani, Boulos-Paul; Damier, Philippe; Arnulf, Isabelle; Thivard, Lionel; Bonnet, Anne-Marie; Dormont, Didier; Cornu, Philippe; Pidoux, Bernard; Samson, Yves; Agid, Yves (1999-05-13). "Transient A...
    Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (
    Douglas C. Smith, High Frequency Measurements Web Page; Index and Technical Tidbits. D. C. Smith Consultants, Los Gatos, CA.
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