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Encyclopedia > Balun

A balun, pronounced /'bæl.ʊn/ ("bal-un"), is a passive electronic device that converts between balanced and unbalanced electrical signals, such as between coaxial cable and ladder line. Look up device in Wiktionary, the free dictionary. ... In telecommunications, a balanced line or balanced signal pair is a transmission line consisting of two conductors in the presence of ground, which relies on balanced impedances to minimize interference. ... Unbalanced line has two common, unrelated meanings in different fields: In American football, an unbalanced line is an offensive line in which more linemen are one side of the ball than the other; see also Glossary of American football. ... The article on electrical energy is located elsewhere. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ... Coaxial Cable For the weapon, see coaxial weapon. ... This article or section does not adequately cite its references or sources. ...


Baluns can be considered as simple forms of transmission line transformers. A transmission line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electromagnetic waves or acoustic waves, as well as electric power transmission. ... Three-phase pole-mounted step-down transformer. ...


Baluns are present in radars, transmitters, satellites, in every telephone network, and probably in most wireless network modem/routers used in homes.

Contents

Function

A balun's function is generally to achieve compatibility between systems, and as such, finds expansive application in modern communications, particularly in realising frequency conversion mixers to make cellular phone and data transmission networks possible. The term compatibility has the following meanings: In telecommunication, the capability of two or more items or components of equipment or material to exist or function in the same system or environment without mutual interference. ... System (from Latin systēma, in turn from Greek systēma) is a set of entities, real or abstract, comprising a whole where each component interacts with or is related to at least one other component and they all serve a common objective. ...


Construction

Baluns can take so many forms that sometimes their presence is not obvious. They always involve some form of electromagnetic coupling, and therefore often include transformer structures. The most basic baluns use a transformer, with the unbalanced connection made to one winding, and the balanced to another. This first form spans a huge variety of sizes, types and materials, with many different winding schemes to achieve balance, impedance transformations, and signal couplings in circuits. Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ...


A large class of baluns uses connected transmission lines of specific lengths, with no obvious "transformer" part. These are usually built for (narrow) frequency ranges where the lengths involved are some multiple of a quarter wavelength of the intended frequency in the transmission line medium. A common application is in making a coaxial connection to a balanced antenna, and designs include many types involving coaxial loops and variously connected "stubs".


A more complex (and subtle) type results when the transformer type (magnetic coupling) is combined with the transmission line type (electro-magnetic coupling). This is where whole transmission lines are used as windings, resulting in devices capable of very wideband operation. This whole class known generally as "Transmission Line Transformers" spawn their own huge variety. Very commonly, they use small ferrite cores in toroidal or "binocular" shapes. Something as simple as 10 turns of coaxial cable coiled up on a diameter about the size of a dinner plate makes an extremely effective choke balun to beyond 30 MHz. The magnetic material may be "air", but it is a transmission line transformer.


Radio equipment applications

A 75-to-300 ohm balun.

In television, amateur radio, and other antenna installations and connections, baluns are used to convert between 300 ohm ribbon cable (balanced) and 75 Ω coaxial cable (unbalanced) or to directly connect a balanced antenna to (unbalanced) coax. To avoid EMC problems it is a good idea to connect a centre fed dipole antenna to coaxial cable via a balun. A TV balun This is an original photograph by Andrew Alder, taken on 19 September 2003. ... A TV balun This is an original photograph by Andrew Alder, taken on 19 September 2003. ... The ohm (symbol: Ω) is the SI unit of electric resistance. ... Amateur radio station with modern solid-state transceiver featuring LCD display and DSP capabilities Amateur radio, often called Ham radio, is a hobby enjoyed by about six million people[1] throughout the world. ... A yagi antenna Most simply, an antenna is an electronic component designed to send or receive radio waves. ... The ohm (symbol: Ω) is the SI unit of electric resistance. ... Left: 20-way grey ribbon cable with wire no. ... Coaxial Cable For the weapon, see coaxial weapon. ... Electromagnetic Compatibility (EMC) is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such an energy may induce. ... A simple half-wave dipole antenna that a shortwave listener might build. ...


The baluns used for home television antennas have a 4:1 impedance ratio, to match the standard 300 Ω twin-lead cable to 75 Ω coaxial cable. Twin-lead is a two-conductor ribbon cable of 300 ohms characteristic impedance commonly used as a transmission line for balanced connection of television antennas to their receiving antennas. ...


Narrow-band designs

  • One easy way to make a balun is a (λ/2) length of coaxial cable. The inner core of the cable is linked at each end to one of the balanced connections for a feeder or dipole. One of these terminals should be connected to the inner core of the coaxial feeder. All three braids should be connected together. This then forms a 4:1 balun which works at only one frequency.
  • Another narrow band design is to use a λ/4 length of metal pipe. The coaxial cable is placed inside the pipe; at one end the braid is wired to the pipe while at the other end no connection is made to the pipe. The balanced end of this balun is at the end where the pipe is wired to the braid. The λ/4 conductor acts as a transformer converting the infinite impedance at the unconnected end into a zero impedance at the end connected to the braid. Hence any current entering the balun through the connection, which goes to the braid at the end with the connection to the pipe, will flow into the pipe. This balun design is not good for low frequencies because of the long length of pipe that will be needed. An easy way to make such a balun is to paint the outside of the coax with conductive paint, then to connect this paint to the braid.

Wide-band designs

Simple homemade 1:1 balun using a toroidal core and coaxial cable. This is a simple RF choke which works as a balun by preventing signals passing along the outside of the braid. Such a device can be used to cure television interference by acting as a braid-breaker.
A 4:1 wideband balun using two windings on a ferrite rod.
  • Two coils on a ferrite rod can be used as a balun in the following way. The two windings need to be very tightly wound together, this can be done with enameled wire in two different ways. Either the two windings are wound with great care so that the two form a single layer where each turn is touching each of the adjacent turns of the other winding or the two wires are twisted together before winding the coil. The start of the first winding then needs to be connected to the end of the second winding. This connection then needs to be attached to the braid of the coaxial feeder, the core of the coaxial feeder is wired to one of the remaining connections. The two conductors for the balanced feeder are then wired to the coil connections which are not wired directly to the braid of the coax. This design can be thought of as an autotransformer. In addition to acting as a balun this design acts as a step up transformer which gives a 4:1 change in the impedance.
  • An RF choke can be used in place of a balun. If a coil is made using coaxial cable near to the feed point of a balanced antenna then the RF current that flows on the outer surface of the coaxial cable can be attenuated. One way of doing this would be to wrap a lossy material, such as ferrite around the coaxial cable;

This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... A toroid is a doughnut-shaped object whose surface is a torus. ... A Choke is an inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. ... Television interference (TVI) is a term for anything which interfers with the viewing of a TV signal, while does not include the interferance to ones pleasure caused by things such ones dog barking during a TV show it does include a series of things which can adversely affect the... The braid breaker is a term for one of the best filters for preventing TVI. It is the case that in many cases of Television interference caused by a high field strength of a nearby HF transmitter that the aerial down lead plugged into the back of the TV acts... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... A coil is a series of loops. ... A stack of ferrite magnets Ferrites are electrically non-conductive ferrimagnetic ceramic compound materials, consisting of various mixtures of iron oxides such as Hematite (Fe2O3) or Magnetite (Fe3O4) and the oxides of other metals. ... The enameled wire is a thin wire with a plastic coverage used for made the electric motor coils. ... This article or section does not cite its references or sources. ... Three-phase pole-mounted step-down transformer. ... Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ... A Choke is an inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. ... A stack of ferrite magnets Ferrites are electrically non-conductive ferrimagnetic ceramic compound materials, consisting of various mixtures of iron oxides such as Hematite (Fe2O3) or Magnetite (Fe3O4) and the oxides of other metals. ...

Audio equipment

Three audio transformers.

In audio applications, baluns are used to convert between high impedance (see Nominal impedance) unbalanced and low impedance balanced lines. Three audio transformers, two of them baluns Except for the connections, all three are electrically identical, but only the leftmost two can be used as baluns. ... Three audio transformers, two of them baluns Except for the connections, all three are electrically identical, but only the leftmost two can be used as baluns. ... Three-phase pole-mounted step-down transformer. ... Sound reproduction is the electrical or mechanical re-creation and/or amplification of sound, often as music. ... In electrical engineering or audio, the nominal impedance of an input or output is the equivalent impedance of all of the output or input circuitry of a device lumped into one (imaginary) component. ... In telecommunications, a balanced line or balanced signal pair is a transmission line consisting of two conductors in the presence of ground, which relies on balanced impedances to minimize interference. ...


Except for the connections, the three devices in the image are electrically identical, but only the leftmost two can be used as baluns. The device on the left would normally be used to connect a high impedance source, such as a guitar, into a balanced microphone input, serving as a passive DI unit. The one in the centre is for connecting a low impedance balanced source, such as a microphone, into a guitar amplifier. The one at the right is not technically a balun, as it provides only impedance matching. Passive has several meanings: In grammar it describes a grammatical voice. ... A DI unit or DI box is an electronic device designed for connecting a piece of equipment with an electronic audio output to a standard microphone or line level input. ... A microphone, sometimes referred to as a mike or mic (both IPA pronunciation: ), is an acoustic to electric transducer or sensor that converts sound into an electrical signal. ... This article or section does not adequately cite its references or sources. ...


Video equipment

Baluns can be used to convert video coming from an S-video, RCA or VGA connector to run over Cat5 cables. S-Video (also known as Y/C) is a baseband analog video format offering a higher quality signal than composite video, but a lower quality than RGB and component video. ... Video Graphics Array (VGA) is a computer display standard first marketed in 1987 by IBM. VGA belongs to a family of earlier IBM video standards and largely remains backward compatible with them. ... Category 5 cable, commonly known as Cat 5, is an unshielded twisted pair type cable designed for high signal integrity. ...


Power line communications

In power line communications, baluns are used in coupling signals onto a power line. For other uses, see Power band. ...


In electronic communications, baluns are used to convert Twinax cables to Category 5 cables, and back. Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... Cat5 patch cable Category 5 cable, commonly known as Cat 5, is a twisted pair cable type designed for high signal integrity. ...


References

  • Building and Using Baluns and Ununs: Practical Designs for the Experimenter, Jerry Sevick (W2FMI), 1994.
  • Radio communication handbook, Edition five, Radio Society of Great Britain (RSGB), 1976, pages 12.41 and 13.5
  • Practical balun uses Basic uses of Baluns to transmit home A/V over Cat5
  • SWDXER ¨The SWDXER¨ - with general SWL information and radio antenna tips.

  Results from FactBites:
 
balun: teory (0 words)
May be baluns are still a mystery for hams; the only way to understand it is learning what it is and how to use it.
The word balun means balanced-unbalanced: it's used to adapt a balanced device to an unbalanced one; in a balanced device (as larger type of antennas) we have on both terminal the same voltage respect to the ground (if not so it's an unbalanced device);
This new wire, when its impedance is low, change the dipole impedance so we can have high S.W.R; this is the reason why (without balun) varying the coaxial cable length the S.W.R. changes.
Test, measure balun, and compare antenna baluns or balums (1142 words)
Heating limits in an HF balun, regardless of load impedance, is almost exclusively due to losses in the core.
The air-core balun is good only for a three or four-to-one frequency range, unless you pick a winding style and size that places unwanted series resonances outside desired bands.
This type of balun is unsuitable for non-symmetrical systems such as off-center-fed antennas, verticals, or antennas with the feedline paralleling the antenna (even at a fairly large distance).
  More results at FactBites »

 
 

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