Patent GB-135896-A (GB)
Title: Improvements in Electromagnetic Wave Navigational Arrangements.
Inventor: ERSKINE-MURRAY JAMES
IPC: G01S1/02
Filed: 1918-11-04
Abstract: 135,896. Murray, J. Erskine-, and Robinson, J. Nov. 4, 1918. Bearings, determining wirelessly; airective wireless signalling.-Vessels and aircraft fitted with ordinary wireless receiving- apparatus are enabied to determine the direction of a transmitting-station by providing the station with means for sending out signals in pairs in directions a definite azimuthal angle apart, the directions of propagation being gradually rotated. When the pairs of signals are of equal strength in the receiver, the line joining the stations bisects the azimuthal angle, and by reading the time (or the number of signals) that has passed since a definite " cardinal-point " signal was heard, the direction of the transmitting-etation may be ascertained. In the arrangement shown in Fig. 1, a pair of aerial coils a, b secured preferably at right-angles to each other are rotatable about a central vertical axis. The exciting-circuits are connected to the aerials by a switch r, which enables a signal to be sent out by each aerial in turn, for every angular position of the pair. In the form shown in Fig. 2, a number of directive aerials 1, 2, &c., arranged like the spokes of a wheel, are connected to the exciting-circuits by a switch r, which is operated in such a way that the aerials are energized in the order 1, 4; 2, 5; 3, 6; &c. A pair of fixed directive aerials a, a<1>, Fig. 3, preferably at right-angles, may be connected to fixed goniometer coils i, i<1>, the rotatable coils a<0> being connected to the exciting-circuits. The coil a<0> is operated in a manner similar to the switch r, Fig. 2. For low-power apparatus, the aerials a, a' may be dispensed with, and a rotating coil such as a<0> used as a radiator. In another modification, Fig. 5, the rotating goniometer coil a<0> is connected through a revensing-switch r to a coil d coupled to an ordinary non-directive aerial, a pair of signals being sent out for each angular position of the coil a<0> by reversing the switch. The coil a<0> may be replaced by a rotatable radiating coil. The modification shown in Fig. 6 comprises a pair of rotatable aerial coils a, a<1> a fixed angular distance apart, preferably a right-angle. They are connected in series, and their interconnexions are reversed by a switch r. If the signals emitted before and after reversal are of equal strength in the receiving-telephone, one of the coils is ineffective and is therefore transverse to the line joining the stations. Instead of being aerial or radiating coils, the coils a, a<1> may be rotatably mounted in the field of two fixed coils connected respectively to a pair of fixed directive aerials. If the coils a, a<1> are identical, there will be four angular positions in which equality of signals is observed in the receiver. This ambiguity may be avoided bv arranging that one coil has a gneater area than the other. A distinctive signal may be sent out when the direction of maximum propagation is due north and south, or distinctive signals may be sent out at every ten degrees round the compass. By means of a stop-watch, the time elapsing from the last distinctive signal to the moment of equality in signal strength may be measured, and the bearings of the transmitting-station obtained therefrom. Alternatively, the number of pairs of signals received after the last distinctive signal may be utilized. With a greater speed of rotation of the propagating direction, the position of equality of signal strength is stated to produce a pure note in the receiver, whereas positions giving unequal strength cause harsh beats, The Provisional Specification refers to an automatic transmitter comprising a rotating disk toothed on the greater part of its periphery, but left plain at the parts corresponding to the " cardinal points." This disk is geared to a toothed pinion operating a reversing-switch and rotating the system which controls the direction of radiation, so that at each step in the disk's rotation, the switch will be reversed.