| 摘要 |
1,229,366. Radio receiving circuits; transistor amplifying and frequency-changing circuits. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 10 Dec., 1969 [13 Dec., 1968], No. 60344/69. Headings H3Q and H3T. In a V.H.F/U.H.F. tuner employing transistors, V.H.F. signals are applied to the base of a transistor 1 operating as a mixer, its emitter being earthed over capacitor 10 and a switch, comprising diode 11 in its conductive state. For U.H.F. signals the transistor 1 operates as an I.F. amplifier, diode 11 being rendered non- conductive and U.H.F. intermediate-frequency signals being applied to its emitter over capacitor 14 and resistor 15 from a separate U.H.F. mixer stage. The V.H.F. signals are applied to the base of transistor 1 via R.F. amplifier 2 and tuned coupling circuit 3: series inductor 4 and capacitor 5, together with circuit 3 presenting a low-impedance to the base of transistor 1 for intermediate frequency. The biasing voltage for diode 11 may be obtained from the supply to the V.H.F. local oscillator 18, both being switched together. |
