GB528252A - Feed-back amplifier filter - Google Patents

Abstract

528,252. Valve circuits for wireless reception. HAZELTINE CORPORATION. April 27, 1939, No. 12692. Convention date, May 9, 1938. [Class 40 (v)] An amplifier-filter section adapted to be matched to other filter sections on an image impedance basis comprises two reactance arms Cl, C2 connected across pairs of input and output terminals 6, 7 respectively, a valve 10 coupling the arms in the forward direction and further means coupling the arms with reversed polarity in the other direction. In the low-pass circuit shown in Fig. 1, the further means comprises a screen-grid valve 11 with the output taken from the screen 9. It is shown in the Specification that the section has image impedances corresponding to constantk mid-shunt image impedances and it may thus be directly connected to one or more further constant-k section 12 ... 14. The screen-grid valve 11 may be replaced by two valves in cascade or by a single valve combined with a phase-reversing transformer. In another arrangement, Fig. 4 (not shown), for a band-pass circuit, the back-coupling means comprises a triode valve with its input and output circuits coupled magnetically to the output and input circuits respectively of the valve 10. In the low-pass circuit shown in Fig. 5, the back coupling comprises resistances 151, 15<SP>11</SP> connected between anode and grid, and in order to provide a degree of regeneration at the cut-off frequency to compensate for loss in the resistances, phase changing means 25 ... 27 may be added. An inductance 22 in series with condenser 23 in the input reactance arm completes an m-derived termination having an image impedance which matches a constant resistance 30 connected across the input terminals. A further arrangement, Fig. 6, for a band-pass circuit comprises two amplifier-filter sections in cascade, the' shunt reactance arms being constituted by condenser 58, the primary and secondary windings of transformer 52, and condenser 68. Damping for the whole system is provided by resistances 59, 70 connected at the ends. Specification 419,784 is referred to.