telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than tha ...

s, a repeating coil is a

voice-frequency A voice frequency (VF) or voice band is the range of audio frequencies used for the transmission of speech. Frequency band In telephony, the usable voice frequency band ranges from approximately 300 to 3400 Hz. It is for this reason that ...

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

characterized by a closed

magnetic core A magnetic core is a piece of magnetic material with a high magnetic permeability used to confine and guide magnetic fields in electrical, electromechanical and magnetic devices such as electromagnets, transformers, electric motors, generators, ...

, a pair of identical

balanced In telecommunications and professional audio, a balanced line or balanced signal pair is a circuit consisting of two conductors of the same type, both of which have equal impedances along their lengths and equal impedances to ground and to other ci ...

primary (

line Line most often refers to: * Line (geometry), object with zero thickness and curvature that stretches to infinity * Telephone line, a single-user circuit on a telephone communication system Line, lines, The Line, or LINE may also refer to: Art ...

)

winding An electromagnetic coil is an electrical conductor such as a wire in the shape of a coil (spiral or helix). Electromagnetic coils are used in electrical engineering, in applications where electric currents interact with magnetic fields, in de ...

s, a pair of identical but not necessarily balanced secondary (drop) windings, and low

transmission loss Transmission loss (TL) in general describes the accumulated decrease in intensity of a waveform energy as a wave propagates outwards from a source, or as it propagates through a certain area or through a certain type of structure. It is a termino ...

at voice frequencies. It permits transfer of voice

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

s from one winding to another by

magnetic Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particles ...

induction, matches line and

drop Drop, DROP, drops or DROPS may refer to: * Drop (liquid) or droplet, a small volume of liquid ** Eye drops, saline (sometimes mydriatic) drops used as medication for the eyes * Drop (unit), a unit of measure of volume * Falling (physics), allowi ...

impedances, and prevents direct conduction between the line and the drop. It is a special application of an

isolation transformer An isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source, usually for safety reasons or to re ...

, and is often used to prevent ground loops or earth loops, which cause humming or buzzing in

audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound *Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum * Digital audio, representation of soun ...

circuits. It also prevents low

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...

s from passing.

References

{{FS1037C MS188 Electromagnetic coils Telephony equipment Electric transformers