Two 1.0M-Hz radio antennas emitting in-phase are separated by 600m along a north-south line. A radio receiver placed 2.0 km east is equidistant from both the transmitting antennas and picks up a fairly strong signal. How far north should that receiver by moved if it is again to detect a signal nearly as strong.
non-paraxial solution, so no small-angle assumption. Also, assume antenna diameters are arbitrarily small emitting spherical waves.
Distance between two maximums.