An Adaptive Electronic Hybrid Transformer

A hybrid transformer is used to couple simultaneously both a transmitter and a receiver to the same end of a telephone line with minimum crosstalk. Under ideal circumstances the transformer provides a cancellation signal at the input terminals of the receiver to exactly cancel the signal induced by the local transmitter. This paper describes a simple electronic device that closely behaves as a hybrid transformer operating under ideal conditions. Rejection on dial-up lines is between 50-80 dB. Adaption time is on the order of 50 ms.