Telephone balance unit

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A telephone balance unit (TBU) is a device to convert the unbalanced audio signal carried on a copper phone line to a balanced audio signal. It will also strip out any DC components (e.g. ringing signals or line power). The term telephone balance unit is commonly used in the UK. In the USA however, the term telephone hybrid is more commonly used.[citation needed]

In the USA these devices are more commonly called baluns 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 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 stations, 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.