This unit is designed to eliminate local electrical noise even before it reaches the antenna socket of the receiver. This is achieved by a phasing technique that cancels noise received on two different antennas but lets the wanted signal through. Unlike other units, this design enables signals to be recovered from below the noise level. A whip antenna is provided to pick up local noise and the main antenna is plugged into the rear SO239 with the output going to the transceiver. An auxiliary antenna socket is also provided so that a short external antenna (rather than the whip) can be used to pick up the noise. It is then merely necessary to adjust the phasing and gain controls to hear the noise just drop away, leaving the wanted signal in the clear.