GB804802A - Improvements in or relating to electrical compandor circuits - Google Patents

Abstract

804,802. Automatic volume control. PHILIPS ELECTRICAL INDUSTRIES Ltd. June 10, 1955 [June 15, 1954], No. 16747/55. Class 40 (4). In a compandor system having expansion or compression circuits comprising variable attenuation networks in the signal circuit and in the compression or expansion control circuit to give a fixed ratio, the networks are controlled jointly at each station by a voltage obtained by rectifying a portion of the transmitted signal and equality of network attenuation is maintained by an additional control signal derived by comparing the outputs of auxiliary signals passed through the network. In the compressor, Fig. 1, networks 3, 14 are both controlled in accordance with the difference between the rectified signal voltage across condenser 29 resulting from the output of amplifier 4, and a constant reference voltage applied at terminal 18. Network 3 is controlled additionally by the output of a difference producer 37 to which auxiliary current outputs from the networks are applied over coils 30, 31. The auxiliary currents which are chosen with frequencies above the intelligence band are applied to the networks over windings 33, 34 and are blocked from the transmission and control paths by filters 39, 40. The auxiliary signal control voltage is added to the main control voltage in a circuit 38 of small time constant. The application of auxiliary equalizing currents to the control networks of an expander of the type described in Specification 804,801 is described with reference to Fig. 2 (not shown).