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Circuit diagram of an autotransformer balun using three taps on a single winding on a ferrite rod. An ideal balun consists of two wires (primary and secondary) and a core: the current in the primary wire generates a magnetic field in the core, which in turn induces an electric field in the secondary wire.
A circuit that has the specific purpose of allowing interfacing between balanced and unbalanced circuits is called a balun. A balun could be a transformer with one leg earthed on the unbalanced side as described in the transformer balance section above. Other circuits are possible such as autotransformers or active circuits. [4]
A balun can be implemented as a transformer which also allows for an impedance transformation. This is usually wound on a ferrite toroidal core. The toroid core material must be suitable for the frequency of use, and in a transmitting antenna it must be of sufficient size to avoid saturation. [21] Other balun designs are mentioned below. [22] [23]
A reference designator unambiguously identifies the location of a component within an electrical schematic or on a printed circuit board.The reference designator usually consists of one or two letters followed by a number, e.g. C3, D1, R4, U15.
A transition from a balanced to an unbalanced line requires a balun circuit. An example of this is CPW to slotline. Example D in the diagram shows this kind of transition and features a balun consisting of a dielectric radial stub. The component shown thus in this circuit is an air bridge bonding the two CPW ground planes together.
Diagram of center-tapped transformer In electronics, a center tap ( CT ) is a contact made to a point halfway along a winding of a transformer or inductor , or along the element of a resistor or a potentiometer .
The goal is to prevent certain current flows (common mode current in the coax shield) while allowing others (opposing currents in the shield vs. center conductor). I should post a good schematic picture. Each type of balun does its job slightly differently. The choke balun prevents the outside current while the coax allows the inside current.
Transformers, autotransformers, and baluns are sometimes incorporated into the design of narrow band antenna tuners and antenna cabling connections. They will all usually have little effect on the resonant frequency of either the antenna or the narrow band transmitter circuits, but can widen the range of impedances that the antenna tuner can match, and/or convert between balanced and ...