GB501644A - Improvements in or relating to radio receivers - Google Patents

Abstract

501,644. Impedance network. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. (Radio Corporation of America). July 30, 1937, No. 21163. [Classes 40 (iii) and 40 (v)] A filter comprises two tuned circuits reactively coupled over two paths which operate in phase opposition, means being provided to correct for the power factors of the circuits so that an undesired frequency is completely eliminated. The filter is described as applied to an intermediate frequency amplifier. The tuned circuits 15, 16, Fig. 1, and 17, 18, 19 are coupled inductively by the mutual inductance M and capacitivoly by condenser C. A resistance R modifies the phase of the signal transferred over M so that, at a frequency 10 kc./sec. off the frequency to which the two circuits are tuned, it is in exact phase opposition to the signal transferred over C; the attenuation characteristic is as shown in Fig. 2. The output circuit of valve 12 comprises a second filter substantially identical with that in its input circuit, but having an attenuation characteristic as shown in Fig. 3, so that the amplifier as a whole has a characteristic as shown in Fig. 4. A switch 33 allows the coil 18 to be shortcircuited to broaden the pass-band for highfidelity reception, a similar switch being incorporated in the output circuit filter. The two filters may be combined into one network, Fig. 8 (not shown). A series of such filters may be used to produce infinite attenuation at several frequencies. Fig. 11 (not shown). The various circuits may be tuned by variation of an iron core of the inductances instead of by adjustment of capacity, Fig. 10 (not shown).