According to a first aspect of the present invention, there is provided a duplexer for a radio frequency antenna, comprising: a radio frequency signal transmitter port arranged for connection to a radio frequency signal transmitter; a radio frequency signal receiver port arranged for connection to a radio frequency signal receiver; a switch arranged selectively to adopt either one of: a first state which connects the transmitter port to a common input/output port of the switch arranged for connection to a radio frequency antenna; and a second state which connects the receiver port to the common input/output port; a switch control unit arranged to monitor radio frequency power at the common input/output port and to receive a transmission gate signal; wherein the switch control unit is arranged to control the switch to adopt the first state upon receipt of the transmission gate signal, and, subsequently, to control the switch to adopt the second state when the monitored radio frequency power falls below a threshold level.