Editing Balanced line (section)

== Explanation ==
[[File:Twisted pair.svg|thumb|250px|'''Fig. 1.''' Balanced line in twisted pair format. This line is intended for use with 2-wire circuits.]]
[[File:Star quad.svg|thumb|250px|'''Fig. 2.''' Balanced line in star quad format. This line is intended for use with 4-wire circuits or two 2-wire circuits. It is also used with microphone signals in [[professional audio]].]]
[[File:DM quad.svg|thumb|250px|'''Fig. 3.''' Balanced line in DM quad format. This line is intended for use with 4-wire circuits or two 2-wire circuits.]]
[[File:Twin lead.svg|thumb|250px|'''Fig. 4.''' Balanced line in twin lead format. This line is intended for use with RF circuits, particularly aerials.]]
Transmission of a signal over a balanced line reduces the influence of noise or interference due to external stray electric fields. Any external signal sources tend to [[Faraday's law of induction|induce]] only a [[common-mode signal]] on the line, and the balanced [[Electrical impedance|impedance]]s to ground minimizes differential pickup due to stray electric fields. The conductors are sometimes [[Twisted pair|twisted together]] to ensure that each conductor is equally exposed to any external magnetic fields that could induce unwanted noise.

Some balanced lines also have [[electrostatic shielding]] to reduce the amount of noise introduced. The cable is often wrapped in foil, copper wire, or a copper braid. This shield provides immunity to RF interference but does not provide immunity to magnetic fields.

Some balanced lines use 4-conductor [[star quad cable]] to provide immunity to magnetic fields. The geometry of the cable ensures that magnetic fields will cause equal interference of both legs of the balanced circuit. This balanced interference is a common-mode signal that can easily be removed by a transformer or balanced differential receiver.<ref>''[http://benchmarkmedia.com/blogs/application_notes/116637511-the-importance-of-star-quad-microphone-cable The Importance of Star-Quad Microphone Cable]''</ref><ref>''[http://www.canare.com/UploadedDocuments/A%20Technical%20Paper%20-%20Evaluating%20Microphone%20Cable%20Perfrmance%20and%20Specifications.pdf Evaluating Microphone Cable Performance & Specifications] {{Webarchive|url=https://web.archive.org/web/20160509154052/http://www.canare.com/UploadedDocuments/A%20Technical%20Paper%20-%20Evaluating%20Microphone%20Cable%20Perfrmance%20and%20Specifications.pdf |date=2016-05-09 }}''</ref><ref>''[http://www.canare.com/UploadedDocuments/Cat11_p35.pdf The Star Quad Story] {{Webarchive|url=https://web.archive.org/web/20161223232056/http://www.canare.com/UploadedDocuments/Cat11_p35.pdf |date=2016-12-23 }}''</ref><ref>''[https://www.soundonsound.com/sos/nov09/articles/qa1109_4.htm What's Special About Star-Quad Cable?]''</ref><ref>''[http://www.belden.com/blog/broadcastav/How-Starquad-Works.cfm How Starquad Works] {{Webarchive|url=https://web.archive.org/web/20161112081214/http://www.belden.com/blog/broadcastav/How-Starquad-Works.cfm |date=2016-11-12 }}''</ref>

A balanced line allows a [[Differential signaling|differential receiver]] to reduce the [[noise]] on a connection by rejecting [[common-mode interference]]. The lines have the same [[Electrical impedance|impedance]] to ground, so the interfering fields or currents induce the same voltage in both wires. Since the receiver responds only to the difference between the wires, it is not influenced by the induced noise voltage. If a balanced line is used in an unbalanced circuit, with different impedances from each conductor to ground, currents induced in the separate conductors will cause different voltage drops to ground, thus creating a voltage differential, making the line more susceptible to noise. Examples of twisted pairs include [[category 5 cable]].

Compared to [[unbalanced line]]s, balanced lines reduce the amount of noise per distance, allowing a longer cable run to be practical. This is because electromagnetic interference will affect both signals the same way. Similarities between the two signals are automatically removed at the end of the transmission path when one signal is subtracted from the other.