Text: A term applied in radio to the coupling of one circuit to another, whereby a portion of the current present in one circuit is fed back or returned to the other circuit. The common use of the term is in reference to regeneration, where a certain portion of the radio frequency current present in the plate circuit of a detector is returned to the grid circuit of the tube by some form of coupling between the two circuits. It may also apply to the tendency of high-frequency currents to become transferred from one circuit to another due to undesired coupling between two or more circuits. The illustration shows a simple feed-back or regenerative circuit. The incoming signal energy is transferred from the primary of the coupler to the secondary by means of inductive coupling and tuned by the condenser C. A grid condenser and leak GC are placed in the grid circuit in the customary manner. A feed-back or reaction coil T is placed in the plate circuit and inductively coupled to the main coil. A portion of the radio frequency current in the plate circuit or output circuit is transferred back to the grid circuit by the coupling effect between the coil T and the secondary of the coupler. This serves in effect to reduce the resistance of the grid circuit and produces more current in the output or plate circuit, thus acting as a form of amplifier.

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Source: 190