GB559967A - Amplitude-and frequency-modulation radio receivers - Google Patents

Abstract

559,967. Frequency modulation; valve circuits for wireless reception. PHILCO RADIO & TELEVISION CORPORATION. Sept. 10, 1942, No. 12754. Convention date, Nov. 14, 1941. [Classes 40 (iii) and 40 (v)] In a receiver for the alternative reception of frequencymodulated and amplitudemodulated waves, the frequency discriminating detector for the FM waves is arranged, without switching operations, to function as a detector for the AM waves. The intermediate frequency circuits are arranged to be resonant to two different frequencies one for FM and the other for AM waves, and switching is confined to the radio frequency stages. In Fig. 2, the IF input to the discriminator includes two tuned circuits 8, 9 resonant to the respective intermediate frequencies. The FM wave is fed from circuit 8 to two untuned secondaries 1, 2 and a tuned secondary 3. These are associated with rectifiers D1, D2 in the manner usual in a phasing discriminator to give a difference output at A across the load resistances 6, 7 to the audio stages. The circuit 9 tuned to the lower AM wave is coupled to a circuit 10 connected only across the diode 2 and load resistance 7, and giving an audio output at A. Owing to the considerable difference between the two intermediate frequencies, each circuit 8, 9 acts substantially as a short circuit for the frequency to which it is not resonant. In a modified discriminator circuit, Fig. 3 (not shown), an AVC voltage is derived by additive combination of the voltages across the resistances 6, 7 in the manner described in Specification 559,535. The discriminator input transformers may be arranged as shown in Fig. 4, the FM input coil 8 being equally and closely coupled to the untuned coils 1, 2 and loosely coupled to the tuned coil 3. The AM coils 9, 10 are closely coupled to give one resonant peak at the working frequency, the other peak being well removed from that frequency. The coils mounted on an insulating tube 16, and the several condensers in the housing 17. The Specification also includes a circuit diagram, Fig. 5 (not shown) of a radio receiver embodying switchless detector and intermediate frequency circuits, together with the switching arrangements for the radio frequency stages . Specifications 181,799, [Class 40 (v)], and 489,094 are referred to.