In a hybrid set, hybrid coil

Hybrid coil

A hybrid coil is a transformer that has three windings, and which is designed to be configured as a circuit having four branches, that are conjugate in pairs....

, or resistance hybrid, balancing network is a circuit

Electronic circuit

An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...

 used to match, i.e., to balance, the impedance

Electrical impedance

Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...

 of a uniform transmission line, (e.g., a twisted metallic pair, coaxial cable, etc.) over a selected range of frequencies. A balancing network is required to ensure isolation between the two ports of the four-wire side of the hybrid.

A balancing network can also be a device used between a balanced device or line and an unbalanced device or line for the purpose of transforming from balanced to unbalanced or from unbalanced to balanced.

Source: from Federal Standard 1037C

Federal Standard 1037C

Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended....

 and from MIL-STD-188

MIL-STD-188

MIL-STD-188 is a series of U.S. military standards relating to telecommunications.-Purpose:Faced with “past technical deficiencies in telecommunications systems and equipment and software…that were traced to basic inadequacies in the application of telecommunication standards and to the lack of a...