A new dynamic impedance matching circuit as applied to a conference repeater

Most telephone conversations are made between two parties. Occasionally the conversation may involve three parties, where the third party talks on an extension telephone. Another form of group conversation involves the interconnection of several telephone lines for a conference call. Here the lines are connected together in a conference circuit at the telephone exchange in a manner to provide optimum transmission and impedance matching. Small conference groups can be coupled through repeating coils but larger groups and conference circuits employed on toll switchboards need an amplifier to maintain satisfactory transmission levels. Current practice is to use telephone repeaters for this purpose.