| 摘要 |
PURPOSE:To prevent interception of uncontracted channel by setting a band pass filter so as to pass a local oscillation signal by television channel selection and bringing the terminal equipment to the normal operating state depending on the presence of the passing local oscillation signal. CONSTITUTION:A signal of a television channel scrambled and contracted is selected by a tuner 4, converted into a prescribed frequency and when it is selected by a television receiver 5, the local oscillation signal leaked and flowed reversely from the television receiver 5 passes through a band pass filter 22 and its presence is detected by a local oscillation detecting circuit 24. As a result, a detection signal is outputted from the circuit 24, the terminal equipment 20 is brought into a normal operating state and the scrambled television channel signal is outputted while being descrambled and received normally by the television receiver 5. In selecting a channel while being deviated by one from the prescribed frequency channel, the local oscillation signal cannot pass through the band pass filter 22. |
