The duplexer has a coupling mechanism (20) which connects the transducer element (T) and receiver (4) in reception mode and decouples the transducer element and transmitter (3) from the receiver in transmission mode. Another coupling mechanism (21) connects the transducer element and transmitter in transmission mode and decouples the transducer element and receiver from the transmitter in reception mode. The two mechanisms (20,21) are connected to a common switching point. The first mechanism contains a FET (8) whose source-drain path is connected between the transducer element and the receiver. The second contains a voltage source for application of a control voltage to the FET's gate to set it into the blocking and conducting states for transmission and reception modes respectively.
