Direction finder

632,366. Radio direction-finding. STANDARD TELEPHONES & CABLES, Ltd. May 17, 1946, No. 15011. Convention date, May 21, 1945. [Class 40 (vii)] In a radio direction-finder of the type wherein the spot of a cathode-ray tube is deflected in a circular path in synchronism with the rotation of a rotating directional aerial and controlled by the received signals to trace out a pattern which indicates the direction from which signals are being received, means are provided for converting the output of the receiver into sharp unidirectional pulses corresponding to instants of null-reception and for applying these pulses to deflect the cathode-ray beam radially so that the direction of reception is indicated by a radial linear trace. The aerial 1 is continuously rotated about its vertical axis by the driving means 3 which also drives the deflecting coil 12 in a rotary motion about the cathode-ray tube 13. The output from the receiver 5 which comprises a full-wave-rectified sine wave is applied to the " clipper " circuit 7 which passes the cusps of the rectified sine wave so as to deliver pulses at twice the frequency of the aerial rotation. The pulses are amplified at 9 and applied to a D.C. restoration circuit 10 which provides positively directed pulses, the peaks of which are at zero potential. The pulses are then applied to the deflecting coil 12, through the amplifier 11, which is cut off during the negative base portions of the pulse signal and which provides a predetermined deflection when the input potential rises to zero, so that a linear trace is obtained whose angular coordinate indicates the direction of reception and whose length is independent of the amplitude of the received signal. To eliminate indications caused by false nulls produced by signal modulation there is provided a tuned amplifier 15 which is tuned to twice the frequency of the aerial rotation, and to which are applied the pulses from the amplifier 9. The output of the amplifier 15 is a sine wave which is " clipped " at 16 and 18 to provide broad pulses which encompass the narrow, direction-indicating, pulses. These pulses are applied through the D.C. restorer 20 to brighten the trace of the cathode-ray tube during the application of the narrow pulses. In another embodiment, Fig. 3 (not shown), the output from the receiver is applied to a tuned amplifier which delivers a sinusoidal output. This is clipped to provide narrow pulses which are used as before to deflect the cathode-ray beam and