The problem of finding the bearing of a distant h.f. transmitter in conditions of wave interference is examined for the simplified case of non-interacting aerials on a plane earth and with no pick-up of horizontally polarized radiation. Two methods of approach are considered????????solution of the field equations for a number of incident plane waves from a knowledge of the field at the aerials, and the fitting of rectilinear constant-phase lines to observed values by a ????????least squares???????? process. It is shown that the cyclical system of Earp and Godfrey is a ????????least squares???????? system of the latter type. Systems of the Wullenwever kind bear a close resemblance to a least-squares system with weighting according to the signal amplitude at each aerial; the difference lies in the fact that they operate with sinusoidal functions of phase instead of linear functions.
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