GB504230A - Improvements in automatic fidelity control for radio reception - Google Patents

Abstract

504,230. Valve amplifying circuits. HAZELTINE CORPORATION. May 30, 1938, No. 16134. Convention date, June 18, 1937. [Class 40 (v)] In a band-pass selector with aperiodic output and input circuits and directive coupling in both forward and backward directions, the back-coupling is less frequency discriminative than the terminal circuits so as to be regenerative only at the limits of the pass-band. The two coupling means are adjustable preferably in such a manner that the gain of the system as a whole is unaffected. The Figure shows a superheterodyne receiver having an intermediate frequency amplifier 14 and signal and automatic volume control detector 15 and also a frequency modulation detector 22 and rectifier 23 as described in Specification 504,229. The audiofrequency amplifier 26 includes a trap circuit 35, 36 tuned to 10 kc. in the output and a valve 27 producing negative feedback. The bias of the valves 26, 27 is controlled from the rectifier 23 preferably in such a manner that the band width passed is adjusted without variation of gain. Regenerative feedback is produced at lower audio frequencies by the inductance of the transformer primary 32 and condenser 30 and at higher audio frequencies by the trap circuit 35, 36 and the condenser 29. At frequencies above that of the trap circuit this gives a 90‹ lead to the voltage which is counterbalanced by the phase lag produced by condenser 29 so that at these frequencies degeneration is produced.