GB243449A - Improvements in or relating to wireless direction finding systems - Google Patents

Abstract

243,449. Smith, R. T. Aug. 29, 1924. Directive signalling; bearings, determining.- To enable an aircraft to determine when it is close to, or immediately over a wireless transmitting station, it is provided with an aerial coil arranged in a vertical plane and continuously rotated about a vertical axis. The strength of received signals tends to equality for all positions of the coil as the aircraft. approaches the neighbourhood vertically above the transmitter. In an alternative form, the invention is utilized in conjunction with the direction-finding system of Specification 134,560, in which system two vertical coils, a main coil and an auxiliary coil, were fixed to each other at right angles and were rotatable about a vertical axis. Switching means were provided for reversing the series connection between the coils, and when this reversal produced no effect on the signal strength, one of the coils was receiving no wave energy, and its plane was therefore at right angles to the direction of the transmitter. To remove, the ambiguity of 90‹, second switch was arranged to cut out the auxiliary coil, and to replace, it by an equal inductance, so as to avoid alteration of the tuning. If the main coil gave signals, its plane lay in the direction of the transmitter. For the purpose of the present invention, the second switch is arranged to cut out the main coil and to insert an equal inductance in series with the auxiliary coil. While the aircraft is flying towards the transmitter, but is still distant therefrom, its direction is ascertained by obtaining equality of signal reception for the two positions of the reversing switch, and by obtaining zero or minimum signals on the auxiliary coil alone, which then lies across the direction of the transmitter. As the aircraft approaches the transmitter, the signal heard on the auxiliary coil alone increases in strength, and when immediately over the transmitter, the three signals heard (a) with the auxiliary coil alone, (b) with the two coils in series, (c) with the two coils in opposition approximate to equal intensity. An automatic switch for effecting the circuit changes is described in Specification 243,448. The Pro- (visional Specification refers to a modified arrangement in which a single vertical coil is fixed in a transverse plane on the aircraft, the received signals increasing to a maximum as the aircraft approaches a position over the transmitter.