GB552807A - Improvements in carrier-signal frequency-detector systems - Google Patents

Abstract

552,807. Inductors. HAZELTINE CORPORATION. July 22, 1941, No. 9247. Convention date, Aug. 12, 1940. [Class 38 (ii)] [Also in Group XL] A balanced detector for a frequency-modulated system comprises a pair of rectifiers connected to produce in their respective load inpedances voltages of opposite polarity relatively to ground or other point of symmetry, the detected signal being derived from the algebraic sum of the respective voltages. As shown in Fig. 4, the tuned and damped output circuit 37 ... 39 of the I.F. amplifier of a superheterodyne receiver is connected through a condenser 40 to a circuit 41, 42 and through an inductance 43 to a circuit 44, 45 the branches being tuned to frequencies near the upper and lower edges of the frequency range. The rectifiers 29 ... 32 associated with the respective branches are so poled as to produce rectified voltages of opposite polarities at the outer ends of their load resistances 30 ... 33 the inner ends being earthed. The resistances 30, 33 and their shunting capacities are symmetrical about the earth point. Output is taken from the terminals y one of which is earthed and the other connected to the mid-point of resistances 35, 36 so that the output voltages is half the algebraic sum of the voltages at the outer ends. In Fig. 5 the discriminator is of the normal phasing type but with a resistance 51 connected between the earth end of the primary coil 47 and one end of the secondary coil 48. The coils 47, 48 may be arranged as shown in Fig. 8. the coil 48 being bifilar wound, and the coil 47 comprising two oppositely-wound sections energized in parallel and placed on opposite sides of the coil 48. The Specification also describes a frequency discriminator network comprising parallel-tuned circuits coupled magnetically to the coil 37 and tuned above and below the mean frequency, Fig. 1 (not shown).