GB488823A - Improvements in radio direction finder - Google Patents

Abstract

488,823. Directive wireless signalling. HELLER, J. I. Nov. 16, 1937, No. 31463. [Class 40 (v)] Directional indications, free from night effect, are obtained from two vertical aerials 15, 16, Fig. 2, spaced apart on the wings of an aeroplane, and connected to a central receiver through two transmission lines 22, 23, screened and balanced against horizontal pick-up. If one pair of leads is crossed-over, as shown, the current through a shunt coil 25 will be zero when the machine is headed directly towards the transmitter, but will indicate deviations to port or starboard. A series coil 29 in the leads, Fig. 6, will carry the sum of the two aerial currents (if the transmission lines are not crossed-over) and will therefore give a circular or non-directional response. By combining the currents from the two coils 25, 29, through secondaries 26, 30 to a common receiver 28, Fig. 7, provided with a 90‹ phasechanging condenser 31, the cardioid curve shown in Fig. 8 is obtained, and can be periodically " reversed " by means of a local oscillator, Fig. 10 (not shown), to give a visual indication of the bearing line. Fig. 9 shows a complete installation with switching means for securing one or more of these directional indications. The coil 25 is switched over to give either a sum or difference effect, whilst the coil 29 serves as a " sense " indicator. With the switch 34 in the position shown, a relay 39 short-circuits the coil 29, a relay 38 nullifies the crossing of the leads, and the coil 25 gives a circular or non-directional response. With the switch 34 in position 36, the relay 38 " crosses " the leads to produce a figure-ofeight response. In position 37 the switch 34 energizes relays 38 and 39 so that the coil 25 gives a " difference " response, and brings the coil 29 into circuit for sense direction. The aerials 15, 16 may be combined with a similar pair set at right-angles, Fig. 11 (not shown). A movable search-coil coupled to crossed coils in the two transmission lines can then be used to take the bearings of off-course transmitters without the necessity of " swinging " the machine.