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In telecommunications and electrical engineering in general, an unbalanced line is a pair of conductors intended to carry electrical signals, which have unequal impedances along their lengths and to ground and other circuits. Examples of unbalanced lines are coaxial cable or the historic earth return system invented for the telegraph, but ...
However, connecting an unbalanced circuit to, for instance, a twisted pair line, which is an intrinsically balanced format, makes the line susceptible to common-mode interference. [citation needed] For this reason, balanced lines are normally driven from balanced circuits. One option is to redesign the circuit so that it is properly impedance ...
The circuit shown in the bottom diagram only can model the differential mode. In the top circuit, the voltage doublers, the difference amplifiers, and impedances Z o (s) account for the interaction of the transmission line with the external circuit. This circuit is a useful equivalent for an unbalanced transmission line like a coaxial cable.
For example, in order to match an inductive load into a real impedance, a capacitor needs to be used. If the load impedance becomes capacitive, the matching element must be replaced by an inductor. In many cases, there is a need to use the same circuit to match a broad range of load impedance and thus simplify the circuit design.
For example, transformation of 300-Ω twin-lead or 450-Ω ladder line (balanced) to 75-Ω coaxial cable (unbalanced), or to directly connect a balanced antenna to unbalanced coaxial cable. To avoid feed line radiation, baluns are typically used as a form of common mode choke attached at the antenna feed point to prevent the coaxial cable from ...
A transition from a balanced to an unbalanced line requires a balun circuit. An example of this is CPW to slotline. Example D in the diagram shows this kind of transition and features a balun consisting of a dielectric radial stub. The component shown thus in this circuit is an air bridge bonding the two CPW ground planes together.
For radio frequency applications, the format is often unbalanced, such as coaxial. For audio and telecommunications, balanced circuits are usually required, such as with the twisted pair format. The Π pad is intrinsically an unbalanced circuit. However, it can be converted to a balanced circuit by placing half the series resistance in the ...
If an unbalanced circuit is required, we have to accept some overall loss. By choosing k 1 = k 2 = a = 0.5, then the network shown below is obtained. This circuit has an overall loss of four times, whereas the conventional L-C ladder network [1]: 605 has no loss (but is not a constant resistance network).