GB517580A - Improvements in or relating to radio direction finding receivers - Google Patents

Abstract

517,580. Directive wireless systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and COCKERELL, C. S. July 29, 1938, No. 22686. [Class 40 (v)] Relates to direction-finding receivers fitted with manuallyoperable sensitivity control effective upon the carrier stage of the receiver in which the audiofrequency output increases to a maximum and then decreases with increasing radio-frequency signal input. Such receivers may give false minimum signal directions corresponding to a minimum audio output produced from a maximum radio signal and according to the invention such false indications are avoided by providing a warning means which is operated automatically if the received carrier strength exceeds a predetermined value. In Fig. 2, the warning means comprise a discharge tube S which is in series with a resistance R3, the series combination being shunted by a condenser C1 and being in series with a further resistance R2. As shown, this circuit is connected across the anode resistance R1 of the anode-bend detector V which may also be the signal detector. Alternatively the circuit may be connected between the anode and earth of a leaky-grid detector (Fig. 3, not shown), or, if a diode or oxide type of rectifier is used, the circuit may be connected between the anode and earth of the following valve, the grid of which is fed with a D.C. component of the rectified radio signal (Fig. 4, not shown). In all these cases an increase in signal input above a predetermined value causes the discharge tube S to flash intermittently. Fig. 5 shows a receiver for C.W. transmissions in which the I.F. output derived from heterodyning the received signal with a first local oscillation is mixed with a second local oscillation from 2LO, the audio difference frequency being obtained at the rectifiers Xl, X2, the output from which is fed directly to the grid of the following valve V1. The D.C. component of the rectification products which depends upon the received signal strength is thus applied to the valve V1 across which the warning circuit R2, R3, C1, S is connected. The discharge-tube warning arrangement described also acts as a rough direction indicator since it shows within a comparatively small arc the direction of the minimum signal. The discharge tube may be replaced by a cathoderay tube or by an electrical or mechanical relay actuating a warning lamp or buzzer.