Balun
A
balun is an
device designed to convert between
balanced
and
unbalanced
electrical signals, such as between
coaxial cable and
twin-lead (pronounced
lēd like
reed, not
lĕd like
red).
This is almost always done through the use of a small isolation transformer, with the earth ground or chassis ground left floating or unconnected on the balanced side. This transformer can then also perform impedance matching at the same time. A balun generally has no other functional purpose except for compatibility between systems.
The most common uses of baluns are:
The baluns used for television antennas have a 4:1 turns ratio, to match the standard 300 ohm ribbon cable to 75 ohm coaxial cable.
A balun used with TV antennas
Three audio transformers. Except for the connections, all three are electrically identical, but only the leftmost two can be used as baluns. The one at left would normally be used to connect a high impedance source, such as a guitar, into a balanced microphone input. The one in the centre is for connecting a low impedance balanced source, such as a microphone, into a guitar amplifier. The one at the right is not a balun at all, and provides only impedance matching.