Balun

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A balun is an adapter that adapts a balanced line to unbalanced line. If a balanced transmission line (such as twinlead) is connected directly to an unbalanced line (such as coaxial cable) the two lines become a long-wire antenna, which is undesirable for VHF and UHF. All baluns are passive bi-directional devices. They are usually above 90% efficient. There are two types:

4-to-1 balun - This will connect 300-ohm twinlead to 75-ohm coaxial cable. This balun is usually a ferrite transformer.

1-to-1 balun - This will connect a 75-ohm balanced load to 75-ohm coaxial cable. This balun is often just some ferrite beads slipped over the coax.