JPS59115684A - System for preventing interception in catv system - Google Patents

Abstract

PURPOSE:To avoid interception by controlling open-shut of the gate circuit of a descrambling control signal at a control section descrambled at a terminal by means of an AC signal of a required frequency not to allow a gate circuit is driven by an externally inserted voltage only. CONSTITUTION:A key signal for descrambling is given by AM-modulating a voice signal from an AGC amplifier 1. The descrambling of the video signal is attained by giving a demodulation signal to a descrambling amplifier 2 of a descrambling control section 6. In this case, the descrambling control section 6 is driven by an AC signal having a specific period. That is, in impressing on AC signal of a specific frequency to a descrambling control terminal A, the signal is rectified at diodes D1, D2, the base voltage of a transistor Q3 is increased and the TRQ3 is switched on by a voltage charged to a capacitor C3, then a TRQ1 is turned on, a signal demodulated by a detector 5 reaches the descrambling amplifier 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing eavesdropping in a CATV system in which video signals with scrambled signals are transmitted.

When a CATV system is used for a pay television network, a scramble signal is added to the video signal to prevent unauthorized viewing, so that a normal image cannot be obtained if the CATV system is used as it is. In this case, the terminal is equipped with a descrambling controller, but the drive signal for this controller is generally a digital signal, and it is activated simply by applying a voltage from the outside. The disadvantage is that it is relatively easy to perform.

The present invention has been made based on the above circumstances, and specifies the drive signal of the descrambling control section in the terminal.
The present invention is intended to provide a method for preventing eavesdropping in an 0ATV system that is not driven solely by an externally inserted voltage and is capable of avoiding eavesdropping.

For this purpose, the present invention provides a CATV system in which a video signal with a scrambled signal is transmitted. It is characterized by opening and closing control using signals.

Hereinafter, one embodiment of the present invention will be specifically described with reference to the drawings. In the figure, reference numeral 1 is an AGC amplifier (automatic gain control amplifier) in the terminal device, which receives the signal from the center (inputs it and sends it to the descrambling amplifier 2 for 1.s 4).
It is output as a video signal. In this case, the output of descrambling amplifier 2 is branched to AGC and AF.
C detector (automatic frequency control and automatic frequency control detector)
3 and used for level stabilization control of the AGO amplifier 1.

The key signal for descrambling is to GC amplifier 1.
It is provided by AM modulating the audio signal.

This key signal is applied to the Fa filter 4. The signal is demodulated via the Fa detector 5 and input to the descramble control section 6. The descrambling control section 6 achieves descrambling of the video signal by applying this demodulated signal to the descrambling amplifier 2.

In this case, the descrambling control section 6 is driven by an alternating current signal having a specific period, and supplies a descrambling signal to the descrambling amplifier 2.

The equivalent circuit of the descramble control section 6 has a configuration of a goo-to circuit as shown in FIG. That is, when an AC signal of a specific frequency is applied to the descramble control terminal A, the voltage that is rectified by the diode D1.01 and charged in the capacitor C3 causes the transistor Q to
The base voltage of the transistor Q3 rises and switches on, and then the transistor Q1 is also switched on, and the signal demodulated by the detector 5 reaches the descrambling amplifier 2.

In this case, the frequency of the alternating current is determined by a time constant determined by capacitor C3 and resistor R7.

Also, 1°0 for this descrambling control section @ section 6.
Even if digital signals or DC voltages are applied, since AC coupling is avoided by capacitor C4, diode D1. Since Dz does not operate, transistor Q3.
Q1 remains off and does not provide a descrambled signal to amplifier 2.

In addition, in the figure, the symbol Qz is a transistor, G1°Gz is a capacitor, and R1 to ReJ5 and R8 are resistors.

As described in detail above, the present invention has a configuration in which the descrambling control section is driven by an AC signal of a required frequency, so that it is not driven by a normal 1.0 digital signal or DC voltage. This is highly effective in preventing eavesdropping.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of the main parts. DESCRIPTION OF SYMBOLS 1... AGC amplifier, 2... Descrambling amplifier, 3... AGC and AFC detector, 4... Fa milter 5... [a detector, 6... Descrambling control section, Dl , Dl...diode, 01-C4
...Capacitor, 01-Q3...Transistor, R
1~Rs...Resistance. Patent Applicant Pioneer Co., Ltd. Agent Patent Attorney Makoto Kobashi Ukiyoshi Patent Attorney Susumu Murai Figure 1 Figure 2

Claims (1)

[Claims] CAT transmitted as a video signal with scrambled signal
In the V system, the gate circuit for the descramble control signal is connected to the control unit that descrambles at the terminal.
A method to prevent eavesdropping, which is characterized by opening and closing control using an alternating current signal of a required frequency.