Abstract: A direction finding system has two antennas with response patterns at 90.degree.. A sense antenna 14 is mounted to produce a sense output dependent on the received radio signal but independent of its bearing. A commutating and combining arrangement receives the antenna outputs and produces a sequence of control signals each of which represents a respective one of the following: the North-South output, the East-West output, the sum of the NS and EW outputs, the difference between the NS and EW outputs, the sum of the NS and sense outputs, and the sum of the EW and sense outputs. A receiver produces an output having a magnitude dependent on any amplitude modulation on the received radio signal but independent of its bearing.