| 摘要 |
620,010. Radio receiving apparatus. PHILIPS LAMPS, Ltd. Jan. 1, 1947, No. 67. Convention date, Sept. 10, 1943. [Class 40 (v)] In a combined transmitter-receiver unit, one of the high or intermediate frequency amplifying valves is used to amplify the low frequency modulating oscillations to be transmitted. The figure shows a transmitter-receiver with a crystal-controlled oscillator 2 feeding a modulator and output amplifier 5 which supplies energy for transmission from aerial 1. The superheterodyne receiver comprises a mixing valve 8, intermediate frequency stage 14, detector stage 16 and output stage 18 which supplies energy to headphones 19. The suppressor grid of mixing valve 8 is coupled to oscillator 2 which acts also as the local oscillator for the receiver, the tuning frequency of the receiver being made to differ from the transmitter frequency by an amount corresponding to the intermediate frequency. The intermediate frequency valve 14 also serves to amplify the modulating oscillations. Speech signals from microphone 26 are applied to the control grid of valve 14, condenser 28 acting as a by-pass condenser for the intermediate frequency, and the amplified speech signals are applied via transformer 29 to the suppressor grid of modulator valve 5. Condenser 30 acts as a shunt for the intermediate frequency. The arrangement is such that both the transmitter and receiver are normally operative, the transmitter frequency being the same as that of the receiver local oscillator. When speech signals are applied to microphone 26, these modulate the transmission, and are also heard in the receiver output simultaneously with the incoming signals from a distant station. A voice-controlled relay may be included in the circuit of valve 14 to modify the receiver connections. |
