| 摘要 |
PURPOSE:To discriminate the presence of a scramble surely with simple circuit constitution by detecting a specific bit of a data pulse obtained from the demodulation of a carrier audio signal. CONSTITUTION:When a data pulse pd is sent from the sender side, that is, a scramble is applied to a CATV signal, the output of the most siginificant digit goes to 'high'. Thus, when the output is received, the output of the 1st inverter 341 goes to 'low', the output of a 2nd inverter 343 goes to 'high' and a MPU detects that the CATV signal received at present is scrambled. Then since an integration circuit 342 is provided between both inverters 341 and 343, even if a start pulse in the data pulse sent for each field is missing tentatively, the output of the 2nd inverter 343 keeps the high level. Thus, the detection is executed correctly. |
