GB535672A - Improvements in or relating to automatic volume control for differential radio receivers - Google Patents

Abstract

535,672. Directive wireless systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Jan. 1, 1940, No. 63. Convention date, Dec. 30, 1938. [Class 40 (v)] Automatic volume control is applied to a " differential " receiver, coupled say to a pair of frame aerials for direction-finding or navigational work, by amplifying both the incoming signals separately and combining them in a common circuit, where a control bias is developed which depends upon the sum of two signals, or upon the one that preponderates, the voltage so derived being applied to both amplifying- channels simultaneously. In this way, the actual amplification of both channels is regulated, though their relative amplification is kept constant so as to operate the " bearing " indicator in the required way. As shown in Fig. 1 signals from the frame aerial 1 are fed from the intermediate-frequency amplifier 5 to a diode 15, the rectified voltage produced across the load resistance 11 being applied through an amplifier 21 to a centre-zero or bearing indicator 51. Signals from the other frame aerial 29 are similarly fed to a diode 35 and the resulting voltage across the load resistance 41 is applied through an amplifier 45 to the same indicator 51, so that for equal signals the latter shows no deflection. Equal changes in signal strength, due say to the receiver approaching the transmitter, do not effect the bearing indicator; they will however produce a change in the potential across the load resistances 11, 41 and therefore of the potential of the junction point 57 of two shunt resistances 53, 55, and this is used to control the actual gain of both the amplifiers 5, 33. Any change in the relative value of the input signals, as the aerial system is rotated, will deflect the bearing indicator 51, though it will not alter the "average" A.V.C. voltage produced at the point 57, the value of which is indicated in a meter 63. In a modified arrangement (Fig. 2 not shown), the resistances 53 and 55 are replaced by a pair of diodes, the arrangement being such as to limit the load placed on the output valves.