GB625532A - Improvements in electrical wave translating systems - Google Patents

Abstract

625,532. Modulating systems ; detectors. WESTERN ELECTRIC CO., Inc. Aug. 7, 1947, No. 21773. Convention date, Jan. 23, 1943. [Class 40 (v)] Modulating and de-modulating circuits employing a bridge arrangement of non-linear elements are balanced as regards the capacity of the elements and their reverse resistance in order to effect carrier current suppression, want of capacity balance being redressed by a differential condenser connected across one diagonal of the bridge with its rotor element connected to one end of the other diagonal, and want of reverse-resistance balance by a resistor connected across one diagonal with an adjustable tap connected to one end of the other diagonal. The Figure shows a modulator of the kind described in Specification 538,795, with carrier applied from a source 31 across one diagonal of the rectifier bridge 10, 11, 12, 13, and with signal voltage from a microphone 19 connected across the other diagonal, output being taken across the latter to a load 28. The invention consists in inserting a resistor 50 across one diagonal with a tap 51 connected to either end of the other diagonal ; and in connecting a condenser with its stator plates 54, 56 connected across one diagonal and its adjustable rotor 58 connected to one end of the other diagonal. If the reverse resistance of rectifier 13 is too high to produce a balance, the tap 51 is moved to reduce the shunt resistance across that rectifier, and to increase the resistance across the rectifier 12. Similarly, if the capacities of rectifiers 11, 12 are unequal or are not in a desired ratio, balance may be restored by varying the shunt capacities 54, 58 and 56, 58. The tapped resistor and the differential condenser may be connected across the same or different diagonal of the bridge, and the adjustable tap may be connected to either terminal of the other diagonal. A capacity 29 is connected in series with the vertical diagonal of the bridge to assist in balancing the resistance of the elements for forward flow of current therethrough, as in Specification 538,795. The bridge may be arranged as a demodulator, (Fig. 2, not shown).