| 摘要 |
PURPOSE:To apply a frequency modulation to a CATV signal by providing an oscillating circuit in a channel selecting control circuit and superimposing an oscillating output on a channel selecting control signal of a CATV broadcasting selected by the channel selecting circuit is a non-contracted subscription program. CONSTITUTION:An oscillation operating signal 17 based on audio and visual contract information is applied to a low pass filter 12 from a memory circuit 7. In such a low pass filter 12, the output of an oscillating circuit 19 consisting of an operation amplifier 18 or the like is applied to a plus terminal of an operation amplifier 16 and a transistor 20 is on/off controlled by the oscillation operating signal 17 to oscillate or non-oscillate the oscillating circuit 19. The oscillating output is superimposed on a bias voltage applied to the plus terminal of the operation amplifier 16 and superimposed on the channel selecting control signal 14 outputted from the low pass filter 12. |
