Information AboutBalun |
| CATEGORIES ABOUT BALUN | |
| transformers electrical | |
| electromagnetic coils | |
| radio electronics | |
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and unbalanced Electric al Signal s, such as between Coaxial Cable and Ladder Line . Baluns can be considered as simple forms of transmission line transformers. 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 spawns a huge variety of sizes, types and materials, with many different winding schemes to achieve balance, impedance transformations, signal couplings in circuits. A large class of baluns use connected transmission lines of specific lengths, with no obvious "transformer" part. These are usually built for a (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 (capacitive 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! A balun's function is generally to achieve Compatibility between System s, and as such, finds expansive application in modern communications, particularly in realising frequency conversion mixers to make cellular phone and data transmission networks possible. Baluns are everywhere. In radars, in transmitters, in satellites, in every telephone network, and probably in most wireless network modem/routers used in homes. RADIO EQUIPMENT APPLICATIONS balun.]] In Television , Amateur Radio , and other Antenna installations and connections, 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. 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. Narrow-band designs
Wide-band designs al 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 .]]
AUDIO EQUIPMENT s.]] In Audio applications, baluns are used to convert between high Impedance unbalanced and low impedance Balanced Line s. Except for the connections, the three devices in the image are electrically identical, but only the leftmost two can be used as baluns. The one at 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. POWER LINE COMMUNICATIONS In Power Line Communication s, baluns are used in coupling signals onto a power line. In electronic communications, baluns are used to convert TWIN-X cables to Category 5 Cable s, and back. SEE ALSO EXTERNAL REFERENCES
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