Telephone Balance Unit
Encyclopedia
A Telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 Balance Unit
is a UK term for a device to convert the unbalanced audio signal carried on a copper phone line to balanced audio
Balanced audio
Balanced audio is a method of interconnecting audio equipment using impedance-balanced lines. This type of connection is very important in sound recording and production because it allows for the use of long cables while reducing susceptibility to external noise.Balanced connections use...

 signal. It will also strip out any DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 components (eg. ringing signals / line power.)

In the USA these devices are more commonly called balun
Balun
A balun is a type of electrical transformer that can convert electrical signals that are balanced about ground to signals that are unbalanced , and the reverse. They are also often used to connect lines of differing impedance...

s by people using them. Radio amateurs use similar devices to match between coax and twinlead. TV stores sell them for matching twin lead from an external antenna to a coax input on a TV.

The word hybrid or more precisely telephone hybrid
Telephone hybrid
Telephone hybrids are an essential functional component of the Public Switched Telephone Network . The term also describes the piece of equipment used in broadcast facilities to enable the airing of telephone callers....

 may be used by radio amateurs when making a phone patch to connect their radio to the phone system.

They are most commonly encountered in radio station
Radio station
Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both...

s, where 'phone-ins' from members of the public need to be inserted into the broadcast chain and in news environments, where reporters 'phone in' a report.

The abbreviation TBU is commonly used in the UK. In the USA however, the term Telephone Hybrid is more commonly used.
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