Patent GB-578550-A (GB)
Title: Improvements in radio apparatus for detecting and measuring the range of distant objects
IPC: G01S7/10
Filed: 1942-03-06
Abstract: 578,550. Radiolocation systems. STANDARD TELEPHONES & CABLES, Ltd. March 6, 1942, No. 2994. Convention date, Feb. 24, 1941. [Class 40 (v)] [Also in Group XXXVI] A wireless system for detecting and measuring the range of reflecting objects comprises directive means for radiating pulses in successively different angular directions in a reference plane, the pulse repetition period being a submultiple of the radiating period in each direction, two antennµ for respectively receiving reflected signals coming from opposite sides of the reference plane, and receiving means which distinguish between the pulses from the respective antennae and apply them to produce indications on a cathode-ray oscillograph having a sweep circuit which rotates the beam at the pulse-repetition frequency. The system shown, when installed in an aircraft, indicates the quarter in which a reflecting object lies, whether it is above or below the plane of level flight, and its distance. The height of the aircraft above ground is also indicated. It includes four directional antennµ E1-4, each of which transmits over one quadrant in the reference plane. Pulses (for example at a frequency of 5000 per second) are fed from a transmitter T controlled by a pulse generator L to the four antennµ in succession by means of a key F rotating, for example, at 20 revolutions per second. The reflected pulses are received by one or both of two directional antennµ A1, A2 according to whether the reflecting object is above, below, or in the reference plane. Keying means G operating at a submultiple of the pulse frequency and synchronized with the key F connect the antennµ A1, A2 alternately to a receiver P, which is rendered operative only during the intervals between the pulse transmissions by means not shown. The keying means G may be electronic and may then operate at half the pulse frequency. The received signals are applied to the radial deflection grid 10 of a cathode-ray oscillograph, the beam of which is rotated to give a circular time base MNPQ by a sweep circuit S synchronized with the pulse-generator L so that the beam makes one revolution for each pulse. In order that signals reflected from an object in one of the quarters served by the antennae E1-4 should give rise to an indication in the corresponding quadrant MN, NP, &c. of the oscillograph scale, the sweep circuit S is connected to the deflector plates 1-4 of the oscillograph through a commutator R which is rotated synchronously with the key F so that the zero point of the time-base which the ray traces is situated successively at the points M, N, P and Q during the transmission periods of the aerials E1, 2, 3, 4 respectively. A black-out circuit BN causes the beam to operate only through a single quadrant in each case. The signals from the antennµ A1, A2 cause radial deflections outwardly and inwardly respectively from the circular path. Thus, T1 indicates an object in the right-front quarter above the reference plane and at a distance represented by the position of T1 on a quadrantal scale having its zero at M, whilst T2 indicates another object in the same quarter but in the reference plane, and at a greater distance than the first. T3 indicates an object in the right rear quarter, below the reference plane, and at a distance represented by the position of T3 on a quadrantal scale having its zero at N. Reflection from the ground flown over gives rise to an indication in each quadrant situated. inside the circular base and in each case at the same distance from the zero point of the quadrant, from which four indications the height above ground of the aircraft may be determined. The transmitting antennae may be used for reception. For example, two sets of antinnµ E1-4, one above the other, may be used, the lower being used to replace A2 and the upper serving both for transmission and to replace A1. Or, each set may be used for transmission at a frequency different from that of the other, the keying means G omitted, and circuits provided so that each aerial feeds reflected signals of only one of the frequencies to the receiver.