GB804393A - Improvements in or relating to radio receivers - Google Patents

Abstract

804,393. Transistor radio receiving circuits; multiplex radio signalling. PHILIPS ELECTRICAL INDUSTRIES, Ltd. June 4, 1956 [June 6, 1955], No. 17186/56. Classes 40 (5) and 40 (6). In a radio receiver, at least one transistor amplifying stage 14, Fig. 1, is supplied with energy derived from a second radio high-frequency transmission. The circuit 1 may be tuned to any desired frequency, while circuit 6 is tuned to a strong transmission to provide as large an operating potential as possible. Highfrequency energy from circuit 6 is rectified and smoothed by elements 7, 8 and fed to the emitter-collector path of transistor 14. The input signal from circuit 1 is demodulated by diode 2 and elements 3, 4 and applied to the baseemitter circuit of transistor 14 to give an amplified signal in earphones 9. By reversing a switch 10 the emitter-collector path of transistor 14 is shorted and the demodulated signal from tuned circuit 6 is fed over capacitor 30 to the earphones 9. Multiplex signalling. A number of receivers, Fig. 2, may be employed, each carried by a person in a hall and a number of speech channels are provided as modulations on auxiliary channels on a main carrier. Circuit 1 is tuned to the desired auxiliary carrier, the main carrier being received by circuit 6. This circuit not only supplies the operating power for audio stage 11 but also feeds rectified but unsmoothed R.F. to the I.F. transformer primary 16 in the collector lead of mixer transistor 21 to develop the auxiliary carrier and its sideband, which is then demodulated by diode 2. By tuning circuit 1 together with the tuning of transformer 16, 17 another auxiliary carrier may be selected to give, after demodulation, another speech output which is amplified by audio stage 11.