Duplex Audio Link

24 036 TELECOMMUNICATIONS DUPLEX AUDIO LINK Duplex communication is, of course, not a new technique: it has been used, for instance, in telephone systems for many years. Those systems, however, make use of transformers to achieve duplex - the circuit presented here does it with the aid of electronics. The principle is fairly simple. Two senders impose signals Ul and U2 respectively on to the audio cable. The voltage across the cable is then (Ul +U2)/2. The receivers at both sides of the cable deduct their side"s sender signal from the cable signal: the result is the signal sent from the other end of the cable. This principle is the basis of the circuit shown. Note that a circuit like that is required at either end of the link. Opamp Al is connected as a buffer amplifier and serves as sender. The send signal is imposed on to the cable via R4. Terminating the cable by R4 results in the voltage across the cable being only half the voltage output of Al. This does not detract from th...