Concept

Hybrid transformer

Résumé
A hybrid transformer (also known as a bridge transformer, hybrid coil, or just hybrid) is a type of directional coupler which is designed to be configured as a circuit having four ports that are conjugate in pairs, implemented using one or more transformers. It is a particular case of the more general concept of a hybrid coupler. A signal arriving at one port is divided equally between the two adjacent ports but does not appear at the opposite port. In the schematic diagram, the signal into W splits between X and Z, and no signal passes to Y. Similarly, signals into X split to W and Y with none to Z, etc. Correct operation requires matched characteristic impedance at all four ports. Forms of hybrid other than transformer coils are possible; any format of directional coupler can be designed to be a hybrid. These formats include transmission lines and waveguides. The primary use of a voiceband hybrid transformer is to convert between 2-wire and 4-wire operation in sequential sections of a communications circuit, for example in a four-wire terminating set. Such conversion was necessary when repeaters were introduced in a 2-wire circuit, a frequent practice at early 20th century telephony. Without hybrids, the output of one amplifier feeds directly into the input of the other, resulting in uncontrollable feedback oscillation (upper diagram). By using hybrids, the outputs and inputs are isolated, resulting in correct 2-wire repeater operation. Late in the century, this practice became rare but hybrids continued in use in line cards. Hybrids are realized using transformers. Two versions of transformer hybrids were used, the single transformer version providing unbalanced outputs with one end grounded, and the double transformer version providing balanced ports. For use in 2-wire repeaters, the single transformer version suffices, since amplifiers in the repeaters have grounded inputs and outputs. X, Y, and Z share a common ground. As shown at left, signal into W, the 2-wire port, will appear at X and Z.
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Séances de cours associées (2)
Coupleurs micro-ondes: théorie et applications
Couvre la théorie et les applications des coupleurs micro-ondes, y compris les considérations de conception et les utilisations pratiques.
Coupleurs micro-ondes: théorie et applications
Couvre l'approche théorique des coupleurs micro-ondes, y compris les coupleurs idéaux et réels, les anneaux hybrides et les coupleurs hybrides.
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Concepts associés (2)
Ligne de transmission
Une ligne de transmission est un ensemble de deux conducteurs acheminant de concert un signal électrique, d'une source (ou émetteur) vers une charge (ou récepteur). On doit considérer une paire de conducteurs comme une ligne de transmission chaque fois que sa longueur est du même ordre de grandeur, ou plus, que la longueur d'onde de la fréquence la plus élevée du signal à transmettre. La charge étant connectée à l'extrémité de la ligne, la ligne permet de retrouver, sur son entrée, à son autre extrémité, la même résistance que la charge, cela quelle que soit la longueur de la ligne.
Four-wire circuit
In telecommunication, a four-wire circuit is a two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path. The four-wire circuit gets its name from the fact that is uses four conductors to create two complete electrical circuits, one for each direction. The two separate circuits (channels) allow full-duplex operation with low crosstalk.