626,477. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd. July 13, 1946, No. 21013. Convention date, Sept. 26, 1945. [Class 40 (vii)] In a radiolocation system comprising a rotary beacon transmitter and a receiver spaced therefrom, the receiver includes a rotating receiving aerial and an indicator comprising two linear members which rotate about axes, spaced apart a distance proportional to the distance between the transmitter and receiver, in synchronism with the radiating and receiving aerial systems respectively so that upon receipt of a re-radiated signal, the point of inter section of the linear members indicates the position of the re-radiating object. Co-operating with the transmitter 1, which may radiate either pulsemodulated or continuous waves is a responder beacon 3 which is situated at a predetermined position with respect to the beacon and reradiates received signals with a distinguishable characteristic. The transmitter 1 comprises a continuously-rotating aerial 2, Fig. 2, and the receiver 4 comprises an aerial 5, which is continuously rotated at a more rapid rate than is the aerial 2. The aerial 5 is driven by motor 14 which also rotates the disc 29, which is opaque apart from a slit 30 cut therein, Fig. 3. The aerial 5 receives signals radiated from the aerial 2, either directly or after reradiation. The output of the detector 17 is applied to a circuit 21 which passes only the maximum signal received by the circuit, i.e. the signal received when the aerials 2 and 5 directly face one another. Since aerial 5 rotates more rapidly than aerial 2, this occurs once per revolution of the aerial 2. The output of circuit 21 is applied to a start-stop clutch 23 which couples the shaft of the motor 22, rotating very slightly faster than the aerial 2, to the disc 25 so that the disc is synchronized once per revolution and rotates at the same rate as the aerial 2. The disc 25 has a slit 26 and a lamp 20 beneath the discs is caused to flash whenever a signal is received by the aerial 5, so that a spot of light appears at the point where the slits 26 and 30 cross, corresponding to the position where the directive patterns of aerials 2 and 5 cross. A translucent map 28 is placed above the disc and it will be seen that the positions of re-radiating objects will be presented on the map provided the shafts of the discs 25 and 29 are actuated correctly with respect to the map. In order to do this the triangle comprising the transmitter 1, the beacon 3 and the receiver 4, is solved. The transmitter comprises in addition to the aerial 2 an omnidirectional aerial 6 radiating on a different frequency. The signal from the aerial 6 is received by aerials 8 and 9, the output from which is used to control a motor 12 so that aerials 8 and 9 are always directed towards the transmitter. It will be seen that the setting of the shaft of motor 12 corresponds to the direction of the line C. The specially characterized signal re-radiated by the beacon 3 is received by the aerial 5 and is selected by the circuit 37 from the output of the detector 17. The output of 37 is applied to a clutch 39 which positions the shaft 40 in accordance with the position of the shaft of motor 14 at the instant of reception from the beacon 3. Thus the setting of shaft 40 corresponds to the direction of the line B. The shaft 40 and the shaft 36 of the motor 12 are coupled differentially in the unit 46, the setting of the output shaft of which is a measure of the angle a. The resistor 51 of the bridge network 49 is set by the output shaft to be proportional to sin a. Shaft 40 is coupled differentially with the compass 43 in the unit 41, and since the side A is fixed, the output shaft of 41 can be arranged to take up a setting corresponding to the angle c. This output shaft sets the resistor 50 to be proportional to sin c. The resistor 52 is fixed and proportional to A so that when the bridge is balanced the resistor 53 is proportional to the side C. The motor 54 is driven by the out-of-balance voltage to vary the resistor 53 until the bridge is balanced and also through the gearing 57 controls the length of the telescoping arm 33 upon which the disc 29 is mounted. The distance between the shafts of the discs 25 and 29 is thus arranged to be proportional to C. The arm 33 is also rotated about the axis of the disc 25 by the shaft 47 of the motor 12 so the shaft of the disc 29 is positioned angularly about the shaft of the disc 25 in accordance with the angular position of the receiver 4 about the transmitter 1. The discs 25 and 29 may alternatively be transparent and carry a conducting wire each in place of the slits 26 and 30, Fig. 4 (not shown). The receiver output is applied between the discs and when a signal is received a spark is produced at the point where the wires cross. Specification 617,511 is referred to. The Specification as open to inspection under Sect. 91 also describes a display wherein the lower disc is replaced by a rotating intensitymodulated radial trace on a cathode-rav tube. This subject-matter does not appear in the Specification as accepted.