AUTOMATIC DIRECTION FINDER

PURPOSE:To determine the incoming direction of radio waves accurately by switching the input for determining the sensing over to the output of one search coil from a vertical antenna when the rough incoming direction of radio waves is indicated with two search coils so arranged to cross at right angle to a goniometer separately. CONSTITUTION:When outputs of antennas 1 and 2 are applied to two excitation coils 5 and 6 crossing at right angles to a goniometer 4 to start measurement, output of a search coil 9 is balance modulated with a low frequency signal of an oscillator 14 and applied to a receiver 13 with output from a vertical antenna 3 shifted by 90 deg. whereby a servo motor 20 is driven with a low harmonic output demodulated. As the output of the coil 9 decreases, a detector 16 transmits a signal at the state as illustrated or before or after that to operate a switch 10 and an output having a value (t) close to the maximum value of a search coil 8 is applied to a synthesization circuit 12. As the output of the receiver 13 vanishes with the maintaining of the measuring operation, the servo motor 20 is halted and the incoming direction of radio waves is indicated.