GB617312A - Improvements in or relating to superheterodyne radio-receivers with image-frequency suppression - Google Patents

Abstract

617,312. Impedance networks. PHILIPS LAMPS, Ltd. Sept. 26, 1946, No. 28806. Convention date, March 3, 1943. [Class 40 (viii)] An image frequency suppression arrangement for a superheterodyne receiver comprising an oscillatory imput circuit 14 inductively coupled to the aerial circuit through a medium-wave coupling coil 5 and through a long wave coupling coil 3, consists of a parallel connection of a condenser 4 with the coil 3, the whole being in series with a coil 2 which is capacitatively but not inductively coupled to the input circuit and which has a natural frequency exceeding the image frequency to be suppressed and an inductance which is smaller than that of the coil 5. In a modification coil 2 may be a tapped-off portion of coil 5. The circuit 2, 3 and 4 may be disconnected by a switch 1 on changing to medium wave reception. The capacity 13 coupling coil 2 to the circuit 14 may be the natural parasitic capacity inherent in the construction. The condenser 4 may be adjustable to suppress the image frequency over a wide tuning range. If, however, in addition to the inductive coupling, the aerial is coupled to the circuit 14 by a variable condenser, suppression over a wide range can be affected by adjusting this, condenser 4 remaining fixed.