Patent GB-574710-A (GB)
Title: Improvements in cathode ray tube indicating apparatus, particularly for radio direction finders and the like
IPC: G01S1/02
Filed: 1940-10-16
Abstract: 574,710. Directive wireless systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and CLOUGH, N. H. Oct. 16, 1940, No. 15345. [Class 40 (v)] [Also in Group XXXVI] A cathode-ray indicating device for comparing voltages, particularly in homing devices' on aircraft, radio compasses for taking bearings on ground stations, &c., includes a cathode-ray tube having at least two deflecting plates across which a pair of condensers are connected in series, and means for connecting these condensers alternately to the voltages to be compared. In the homing radio receiver shown in Fig. 1, the output of the receiver proper, consisting of the sum and difference of two voltages in alternation, is fed to the centretapped secondary S of an output transformer, the outer ends of which are connected to the anodes a of thermionic rectifiers RY1, RY2, which serve also as switches. The cathodes c of the rectifiers are connected to the free terminals of two condensers CY1, CY2 in series, the junction of which is connected to the centre tap ct on the secondary S and through a leak resistance LRY to earth. The condensers CY1, CY2 are connected to a pair of deflecting plates Y1, Y2 of a cathode-ray tube, across which are connected two high leak resistances LRY1, LRY2, in series with their junction point earthed. The grids g1, g2 of the rectifiers are connected to the cathodes c through oppositely connected secondary windings SY1, SY2 of a transformer T in series with sources of bias potential BY1, BY2. Alternating current is applied to the primary P of the transformer T, which may have a third secondary ST for effecting synchronous switching of the input to the receiver proper. The cathode-ray, is deflected in direction and sense corresponding to that of the transmitter, the deflection being dependent on the strength of the received signal. Fig. 2 shows a directionfinder system having North-South and East- West aerial systems NS, EW and a sense aerial SA, the centres of the coils NS, EW being earthed and their ends being connected to fixed contacts 1 ... 4 of a . continuously rotatable switch A, the rotary arm of which is connected to the input coil IC of the receiver proper. The output coil OC is connected to one pair Y1, Y2 of deflecting plates, condensers CY1, CY2, and leak resistances LRY, LRY1, LRY2 as in Fig. 1. The coil OC is also connected, through a rectifier R, rotary switch arm B, and fixed contacts 1 ... 4, to the second pair of deflecting plates X1, X2, condensers CX1, CX2 and leak resistances LRX, LRX1, LRX2, the switches A, B being rotated in synchronism. Instead of mechanical switching, electronic switching may be employed. For example; the condensers of one deflecting system may be charged as shown in Fig. 1 for a few cycles, after which a switch operated by a neon discharge or time delay circuit changes over to charge the condensers of the other deflecting system. In modifications, one of the deflecting plates, or one of each pair, is earthed and connected to a free terminal of one condenser and to a fixed contact of a switch, the other deflecting plate' being connected to the free terminal of the other condenser 'and to the other fixed contact of the switch. The common junction point of the two condensers. and of the two high leak resistances connected across them is connected through the secondary of a receiver output transformer and a rectifier to the moving contact of the switch. Instead of discharging the condensers by leak resistances, they may be short-circuited by further operations of the switches.