Patent GB-334341-A (GB)
Title: Improvements in or relating to wireless direction finding systems
IPC: G01S3/06
Filed: 1929-07-30
Abstract: 334,341. Smith, R. T. July 30. 1929. Bearings, determining.-In a wireless direction finder, the effect of reception on a loop aerial is neutralized by the effect of reception on another aerial, so that the orientation of the loop aerial relative to the transmitting station is indicated by a device serving to vary the relative effect of the two aerials on the receiver. A loop aerial 1, Fig. 1, for use on aircraft, and arranged athwart. ships, is connected through coils 2, 3 to the ends of a potentiometer resistance 4 the sliding contact 8 of which is connected to-earth, the coils 2, 3 being so coupled to the grid-circuit coil 5 that the open-aerial effect of the loop 1 is zero when the moving contact of the potentiometer is central. If the loop is not at right angles to the direction of the transmitter a signal will be heard, which may however be neutralized by adjusting the potentiometer tapping which can therefore be calibrated in terms of the angle the loop is making with the direction of the transmitter. The potentiometer 4 should have as small an inductance as possible, so that the loop and antenna effects are in phrase. A separate plain aerial may be used, (Fig. 3, not shown) in which case a fixed centre tapping of the potentiometer is earthed and the sliding contact is connected to this aerial. The loop may be inductively coupled to the non-directional aerial circuit (Fig. 5, not shown) an expedient which enables the angular calibration of the potentiometer to be varied by varying said coupling. Alternatively the non-directional aerial circuit may be coupled to the loop circuit (Fig. 6, not shown). In a push-pull arrangement (Figs. 7 and 8, not shown) there are two loops with the potentiometer between them in the common grid circuits of two amplifying valves, or coupled thereto, and a non- directive aerial connected to the variable contact of the potentiometer, a common tuned anode circuit being coupled to the succeeding valves. The potentiometer 4 comprises a cylindrical block 40, Fig. 10, of insulating material mounted in a flanged metal cover 41. A spindle 42 and worm wheel 43, adapted to be driven by a worm engaged by a flexible shaft extending through an extension 45, Fig. 12, of the casing, carries a pointer 47 moving over a scale consisting of two semicircular portions of red and green transparent material, clamped between glass plates 48, and calibrated in degrees to " Port and " Starboard " respectively. The spindle 42 carries at its lower end, a metal roller 56, mounted on a bar 57, pivoted to an arm 58. The roller is pressed on to the resistor by a spring 59, the arm 57 being balanced by holes formed in it, and the contact to the moving element being made by arms 60 drawn against a collar 62 on the spindle by a spring 61. The winding 50, is mounted on a removable former 51, the wire being wound up and down on the inner surface of the former, and looped into slots at each end, to obtain a minimum inductance. Studs 53 in connection with the tappings to the winding on the outside of the former make contact with spring members 54 which is turn are connected to external sockets. In use the potentiometer is in continuous rotation by connection to a windmill or other motor, and the position of the pointer is noted when the zero signal is obtained. If red the pilot turns to port, or if green to starboard, to make the. transmitting station, and the angular deviation is directly readable. The apparatus may be modified to enable the method of adding and subtracting the effects of the loop and non-directional aerial, to be used. In this case the potentiometer winding extends over a semi-circle, the ends being connected to two insulated segments completing the circle and so connected as to produce the changeover required. Two movable contacts, coilnected to earth and the non-directive aerial, and arranged to revolve in opposite directions, may be provided, either to enable the wire to be shortened and the inductance reduced, or to enable a non-directive aerial of less effective height to be used. The potentiometer may be replaced :by a variometer having one winding connected across a fixed resistance in series with the plain aerial, the other being connected to the loop through the two coils in the loop circuit.