Patent GB-585826-A (GB)
Title: Improvements in or relating to the detection of obstacles by means of electromagnetic impulses
IPC: G01S1/24
Filed: 1941-03-11
Abstract: 585,826. Radiolocation. STANDARD TELEPHONE & CABLES, Ltd., and LEVY, M.M. March 11, 1941, No. 3296. [Class 40 (v)] In a system for obstacle detection in which impulses consisting of short trains of electromagnetic waves radiated by a transmitter are detected by a receiver after reflection at the obstacle, the receiver is prevented from operating a short time before the receipt of directly received radiated impulses and is restored to the operating condition a short time after the disappearance thereof. A generator G, Fig. 1, modulates the oscillator O of the transmitter T by periodical rectangular impulses and at the same time sends impulses to a blocking circuit B through a cable C. The impulses delivered to the transmitter and blocking circuit are retarded by artificial lines L1, L2, the delays produced by which are adjusted so that the, radiated impulses TR received at the, receiver R are slightly behind the impulses transmitted to the blocking circuit. The blocking circuit B includes a mixing circuit M which receives the retarded impulses Ib1 delivered by the line L2 and also impulses Ib2 obtained by transmitting the impulses Ib1 through a delay network L3. A lengthened impulse having a central peak is thus produced and may be passed through an amplitude limiter A to cut off the peak. The blocking circuit is shown in Fig. 3 and consists of a valve V1, to which the impulses from the generator are applied, followed by mixing valves V2, V3, the plate circuits of which are connected to a common load Rp. Anode potential is supplied by batteries B1, B2. Grid resistances R1, R2 and condenser-resistance biassing circuits K1, K2, K3 are connected as shown. The output is taken from terminals z1, z2 through a blocking condenser C1. Connected between the cathode of the valve V1 and earth is the input circuit of a delay network L3 to the input and output terminals of which are connected impedances Z1, Z2. The network consists of a number of separate sections in tandem, to the terminals of any of which sections external connections may be made. The grids of the valves V2, V3 are connected to two such sections through blocking condensers C2, C3. Impulses similar to those for producing the radiated impulses Ts, Fig. 1, are applied to the terminals xl, x2 of the blocking circuit and so poled that they make the grid of the valve V1 positive. Impulses Ib1 having the same sign but delayed in transmission through part of the network L3 are applied to the grid of the valve V2, while similar impulses Ib2 with greater delay by transmission through a larger part of the network L3 are applied to the grid of the valve V3. The impulses Ib1, Ib2 are mixed in the resistance Rp and impulses of the type Ib1+2 are obtained from output terminals z1, z2. Alternatively the cathodes instead of the grids of the valves V2, V3 may be connected to points of the network L3, the cathode circuits K2, K3 being omitted. The delay network may be connected in the plate circuit instead of in the cathode circuit. A simpler circuit is shown in Fig. 4, in which a single valve VI has its cathode circuit connected to the input of a delay network L3. The plate potential is supplied by a battery B1 and there is no load in the anode circuit. The network L3 has across its input terminals an impedance Z 1 of such value that the network is terminated by its image impedance, the output terminals being unconnected. The impulses Is are applied to the grid of the valve and a similar impulse Ib1 then appears across the impedance Z1. This impulse is transmitted through the delay network and is reflected at the output terminals, returning to the input terminals as the impulse Ib2 after a delay caused by traversing the network twice. The impulses are mixed in the impedance Z1, across which the output terminals are connected. The lengthened impulses may be applied directly to the valve of the receiver R, Fig. 1, or the circuits shown in Figs. 3 and 4 may be followed by an amplitude limiter A adjusted to cut off the peaks of the impulses Ib1+2.