Four wire to two wire converter

Claim 1

A two wire to four wire converter for connecting a private telephone network having a transmission and reception channel to a public telephone network and isolating the networks with low value capacitors comprising: a first operational amplifier having first and second inputs with one input connected to said reception channel and first and second symmetrical outputs; two circuit branches each comprising a serially connected isolating sigular and a singular each branch respectively connecting one of said outputs of said first amplifier to said public network; a second operational amplifier having first and second inputs and an output; two isolating capacitors each respectively connecting one of said inputs of said second amplifier to said public network; a third operational amplifier having first and second inputs and an output connected to the other input to said first amplifier said third amplifier having a gain of 1/2 when the sum of the series resistances is equal to the resistance of the public network with respect to the converter; two isolating capacitors respectively connecting the common points of the series connected resistors and capacitors to said first and second inputs of said third amplifier; a fourth operational amplifier having first and second inputs with a first input connected to the output of said second amplifier and an output connected to said transmission channel; and a phase shifting network connected between said reception channel and said second input of said fourth amplifier.