Balun

balun

(BALanced UNbalanced) A device that connects a balanced line to an unbalanced line; for example, a twisted pair to a coaxial cable. A balanced line is one in which both wires are electrically equal. In an unbalanced line, such as a coax, one line has different properties than the other.

Balun

The BNC connector on the left connects to coaxial cable. The screw connectors on the right connect to telephone style twisted wire pairs. (Image courtesy of Black Box Corporation.)

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balun [′ba‚lən]

(electricity)

A device used for matching an unbalanced coaxial transmission line or system to a balanced two-wire line or system. Also known as balanced converter; bazooka; line-balance converter.

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(electronics)

balun - A transformer connected between a balanced source or load and an unbalanced source or load. A balanced line has two conductors, with equal currents in opposite directions. The unbalanced line has just one conductor; the current in it returns via a common ground or earth path.

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Balun 

a device in the antenna-feeder line of a radio transmitter or receiver that matches an unbalanced feeder with a balanced feeder or antenna, or a balanced feeder with an unbalanced antenna. Baluns are principally used at meter and decameter wavelengths.

Figure 1. Baluns: (a) single-section, (b) quarter-wave sleeve, (c) U-bend, (d) coaxial-slot coupling, (e) balun with mismatch compensated; (1) unbalanced line, (2) balanced line, (3) sleeve, (4) half-wave loop, (5) bridge, (6) slot, (7) coaxial transformer, (8) compensating open-ended stub, (9) balanced short-circuited stub; (L) inductance coil, (C) capacitor

At decamenter wavelengths baluns are most often composed of elements that have lumped parameters, such as capacitors, inductance coils, and transformers, and form, for example, single- and multiple-section electric filters (Figure 1,a; see page 26). At meter wavelengths baluns are composed of elements having distributed parameters forming, for example, a quarter-wave sleeve (Figure 1,b), a U-bend (Figure 1,c), or a coaxial-slot coupling (Figure l,d). All such baluns operate in a narrow frequency band; in order to widen the frequency band, various devices, consisting of short-circuited and open-ended stubs, are used to compensate for the mismatch (Figure l,e). Transformer baluns with ferrite cores are often used in feeder lines that carry moderate power (up to 10 kilowatts).

REFERENCES

Aizenberg, G. Z. Antenny ul’trakorotkikh voln [part 1]. Moscow, 1957.
Lavrov, G. A., and A. S. Kniazev. Prizemnye i podzemnye antenny. Moscow, 1965.
Drabkin, A. L., V. L. Zuzenko, and A. G. Kislov. Antenno-fidernye ustroistva, 2nd ed. Moscow, 1974.

G. A. KLIGER and V. I. KOMISSAROV