649,338. Radio direction-finders. MINISTER OF SUPPLY. Nov. 28, 1947, No. 31541. [Class 40 (vii)] A radio-direction-finder comprises an aerial system having a continuously rotating figureeight directivity pattern, means for generating signals simulating those received by an additional aerial system having a synchronouslyrotating figure-eight directivity pattern, switching means for reversing the phase of one lobe of the simulated directivity pattern so that both lobes of the pattern have the same phase, means for combining the signals produced in respect of both directivity patterns, a cathoderay indicator to which the combined signals are applied and means for rotating the axes of one directivity pattern with respect to the other so that a characteristic representation is obtained on the indicator when the axes of the patterns are at right angles, whereby the desired directional determination may be made. Signals received on an Adcock aerial system are applied to the field coils F1, F2 of goniometer 1 having a continuously rotating search coil S1. The coil S1 is mounted on shaft 7 and the signal induced in the coil S1 is coupled through sliprings 3, 4 mounted on the shaft 7 and lines 5, 6 to a receiver, the audio output from which is applied at points 18, 19 to deflect the beam of a cathode-ray tube 17. Signals from an omnidirectional aerial 14 are applied through a 90 degrees phase-shifting and amplitudecontrolling arrangement, comprising resistor 15 and condenser 16, commutator 8 and slip-rings 9 and 10 to search coil 52 of goniometer 2, via slip-rings 11, 12 mounted upon the shaft 13 carrying coil 32. The stator coils F3, F4 are connected to the coils F1, F2 of goniometer 1 so that a field is induced in goniometer 1 in respect of the current flowing in coil S2 and having a direction corresponding to the direction of coil S2 which is controlled by manual setting of shaft 13. Rotation of shaft 13 also controls the position of brushes 8a around commutator 8 in such a fashion that the signal applied to coil S2 is switched in phase at the instants when the signal induced thereby in coil S1 falls to zero. It will be seen that fields are established in the goniometer 1 so that as the coil S1 rotates, potentials are induced therein corresponding (a) to those received by a rotating aerial having a normal figure-eight polar diagram due to the signals received by the Adcock system, and (b) to those received by a rotating aerial having a figure-eight polar diagram of which both lobes have the same phase due to the signals received by the aerial 14. In Fig. 1 is illustrated two figure-eight polar diagrams having similarlyphased and opposite-phased diagrams respectively, the resultant directivity pattern when the axes of the diagrams are perpendicular being shown at 1. Thus as coil S1 rotates, signals will be induced therein according to a directivity pattern which will take on the symmetrical form shown in Fig. 1 when the coil S2 is set in an appropriate fashion, i.e. so that the field induced thereby in goniometer 1 is perpendicular to that induced in the goniometer by the signals received on the Adcock system. In order to display the received signals, the cathode-ray tube 17 employs a time-base which is triggered by a pulse induced in coil 20 by an armature 21 mounted on commutator 8. The position of the coil 20 about the shaft 7 is controlled by rotation of the shaft 13 so that the signals displayed on the cathode-ray tube correspond to those received around a particular null of the simulated figure-eight polar diagram. For a symmetrical pattern of the desired form to be obtained the coil 52 must be rotated to such a position that the oppositely-phased lobe of the other polar diagram lies along this null direction. Thus by rotation of the coil S2 until this pattern is obtained both the direction line and sense of the received signal may be determined. In an alternative arrangement, Fig. 4 (not shown), a sinusoidal voltage synchronized with the rotation of the coil S1 and phased according to the angular setting of the coil S2 is obtained and used to derive a switching voltage whereby the phase of the signals applied to the coil S2 is reversed in phase every time the electrical directions of coils S1 and S2 are perpendicular. The sinusoidal voltage is also used to derive a triggering pulse for the time-base of the cathoderay tube display unit.