In telecommunications and professional audio, a balanced line or balanced signal pair is a transmission line consisting of two conductors of the same type, each of which have equal impedances along their lengths and equal impedances to ground and to other circuits. The chief advantage of the balanced line format is good rejection of external noise when fed to a differential amplifier. Common forms of balanced line are twin-lead, used for radio frequency signals and twisted pair, used for lower frequencies. They are to be contrasted to unbalanced lines, such as coaxial cable, which is designed to have its return conductor connected to ground, or circuits whose return conductor actually is ground. Balanced and unbalanced circuits can be interconnected using a transformer called a balun.
Electromagnetic compatibility (EMC) is the branch of electrical engineering concerned with the unintentional generation, propagation and reception of electromagnetic energy which may cause unwanted effects such as electromagnetic interference (EMI) or even physical damage in operational equipment. Also, it is the ability of an equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment. The goal of EMC is the correct operation of different equipment in a common electromagnetic environment.
In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the earth.
Coaxial cable, or coax is a type of electrical cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an insulating outer sheath or jacket. The term coaxial comes from the inner conductor and the outer shield sharing a geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, who patented the design in 1880.
Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted balanced pair, a twisted pair reduces electromagnetic radiation from the pair and crosstalk between neighboring pairs and improves rejection of external electromagnetic interference. It was invented by Alexander Graham Bell.
Balanced audio is a method of interconnecting audio equipment using balanced lines. This type of connection is very important in sound recording and production because it allows the use of long cables while reducing susceptibility to external noise caused by electromagnetic interference.
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. Isolation transformers provide galvanic isolation and are used to protect against electric shock, to suppress electrical noise in sensitive devices, or to transfer power between two circuits which must not be connected. A transformer sold for isolation is often built with special insulation between primary and secondary, and is specified to withstand a high voltage between windings.
Antenna tuner, matching network, matchbox, transmatch, antenna tuning unit (ATU), antenna coupler, and feedline coupler are all equivalent names for a device connected between a radio transmitter and its antenna, to improve power transfer between them by matching the specified load impedance of the radio to the combined input impedance of the feedline.
In an electrical system, a ground loop or earth loop occurs when two points of a circuit both intended to be at ground reference potential have a potential between them. This can be caused, for example, in a signal circuit referenced to ground, if enough current is flowing in the ground to cause two points to be at different potentials.
An autotransformer is an electrical transformer with only one winding. The "auto" prefix refers to the single coil acting alone, not to any kind of automatic mechanism. In an autotransformer, portions of the same winding act as both the primary and secondary sides of the transformer. In contrast, an ordinary transformer has separate primary and secondary windings which are not electrically connected.
In electronics, a shunt is a device which creates a low-resistance path for electric current, to allow it to pass around another point in the circuit. The origin of the term is in the verb 'to shunt' meaning to turn away or follow a different path.
Mains hum, electric hum, or power line hum is a sound associated with alternating current at the frequency of the mains electricity. The fundamental frequency of this sound is usually 50 Hz or 60 Hz, depending on the local power-line frequency. The sound often has heavy harmonic content above 50–60 Hz. Because of the presence of mains current in mains-powered audio equipment as well as ubiquitous AC electromagnetic fields from nearby appliances and wiring, 50/60 Hz electrical noise can get into audio systems, and is heard as mains hum from their speakers. Mains hum may also be heard coming from powerful electric power grid equipment such as utility transformers, caused by mechanical vibrations induced by magnetostriction in magnetic core. Onboard aircraft the frequency heard is often higher pitched, due to the use of 400 Hz AC power in these settings because 400 Hz transformers are much smaller and lighter.
A braid-breaker is a filter that prevents television interference (TVI). In many cases of TVI, caused by a high field strength of a nearby high frequency (HF) transmitter, the aerial down lead plugged into the back of the TV acts as a longwire antenna or as a simple vertical element. The radio frequency (RF) current flowing through the tuner of the TV tends to generate harmonics which then spoil the viewing.
A variety of types of electrical transformer are made for different purposes. Despite their design differences, the various types employ the same basic principle as discovered in 1831 by Michael Faraday, and share several key functional parts.
A balanced circuit is circuitry for use with a balanced line or the balanced line itself. Balanced lines are a common method of transmitting many types of electrical communication signals between two points on two wires. In a balanced line the two signal lines are of a matched impedance to help ensure that interference induced in the line is common-mode and can be removed at the receiving end by circuitry with good common-mode rejection. To maintain the balance, circuit blocks which interface to the line, or are connected in the line, must also be balanced.
Common-mode signal is the component of an analog signal which is present with one sign on all considered conductors. In telecommunication, common-mode signal on a transmission line is known as longitudinal voltage.
Sheath current filters are electronic components that can prevent noise signals travelling in the sheath of sheathed cables, which can cause interference. Using sheath current filters, ground loops causing mains hum and high frequency common-mode signals can be prevented.
A sheath current is a form of charge transfer in wires. Sheath currents can run along the outer sheath of a coaxial cable. This can be caused by a geographically proximate or remote ground potential.
