JPH0119502Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scrambling device for an interference wave insertion type pay television system.

In a pay television system, in order to ensure that only authorized subscribers can properly receive the broadcast, it is necessary to use a scrambling device to disable reception for non-subscribers. FIG. 1 is a block diagram showing the configuration of such a pay television system, in which 1 is a head end, 2 is a modulator, 3 is a control signal generator, 4 is a mixer, 5 is a distributor, 6a to 6d are branchers, 7a to 7d are scramble devices, and 8a to 8d are television receivers. This method uses a control signal, which is contract information transmitted from the center along with broadcast waves, to individually turn on and off the scrambling operation of the scrambling device on the branch line branching out to each subscriber (addressable control signal).・Tap). The control signal generated by the control signal generator 3 is subjected to AM or FM modulation by the modulator 2, and is sent out together with broadcast waves at a frequency _P shown in FIG. This signal is distributed and branched to branch lines of each subscriber, scrambled or unscrambled depending on the contract status by scrambling devices 7a to 7d, and transmitted to each subscriber.

A common scrambling method is the interference wave insertion method. As shown in Figure 4, the jamming wave insertion method inserts a jamming signal of frequency _G between (for example, at the center) a video carrier of frequency _V and an audio carrier of frequency _S in a paid channel, and This is a method of scrambling video and audio.

A specific conventional method is shown in a block diagram in FIG. In FIG. 2, 9 is an input, 10 is an output, 11 is a branching filter, 12 is a filter, 13 is a demodulator, 14 is a controller, 15 is an oscillator, and 16 is a mixer. The control signal _P is separated from the television signal by a branching filter 11, passed through a filter 12, and demodulated by a demodulator 13. When the contract information thus transmitted is non-contract, the controller 14 outputs an oscillator 15.
is turned on, and the mixer 16 inserts the interference signal into the broadcast signal. Here, the oscillation frequency of the oscillator 15 must be _G. Additionally, the higher the level, the better the scrambling performance will be, but if the level is too high, leakage to other branch lines will become a problem, and generally the level of the interference signal should be the same as the level of the video carrier wave. has been done. However, since the video carrier wave levels in each branch line are not necessarily equal, setting the insertion level of the interference wave signal becomes a problem.

The conventional method described above has the following drawbacks.

(b) The oscillation frequency of the interference wave oscillator of the scrambling device must be the same as _G , and since the oscillation frequency is high, there is a problem in maintaining its stability.

(b) It is difficult to make the interference wave insertion level equal to the video carrier wave level in branch lines with different levels.

An object of the present invention is to provide a scrambling device for a pay television system that oscillates at a frequency lower than the frequency of the necessary interference signal and can automatically match the interference wave insertion level to the video carrier level. be.

In order to achieve the above object, the scrambling device for a pay television system according to the present invention comprises:
A branching filter that separates a control signal and a broadcast signal of frequency _P superimposed on the received signal on a branch line branched from the main line, and outputs the signal; a first filter that passes the control signal; a demodulator that demodulates the passed signal; a controller that controls scrambling on and off according to the demodulated signal;
The frequency of the interference signal is controlled by the above controller.
As _G , an oscillator that oscillates at a frequency of _G − _P , the signal of frequency _P that has passed through the above first filter and the output of the above oscillator of frequency _G − _P are mixed, and the frequency
A frequency converter that outputs _{the G} interference signal, a second filter that passes the interference signal, and a mixer that returns the output of the second filter to the branch line and mixes it with the broadcast signal. This is the summary.

FIG. 3 is a block diagram showing the configuration of the scrambling device according to the present invention, in which reference numbers common to those in FIG. 2 represent the same parts as in FIG.
17 is a frequency converter, and 18 is a second filter.

A signal branched from the main line (broadcast signal and control pilot signal _P ) is branched into a broadcast signal and a control pilot signal by a branching filter 11. The control pilot signal passes through a first filter (for passing _P ) 12, is demodulated by a demodulator 13, and a controller 14 controls whether or not to scramble it. Specifically, it is on/off or frequency control of the oscillator 15.

If you are a non-contractor, the controller 14
The oscillator 15 oscillates a frequency _G − _P , which is mixed with the control pilot signal _P by the frequency converter 17 to produce the sum frequency _G , which is then passed through the second filter (for passing _G) . ) 18, it is inserted into a branch line by a mixer 16 to scramble the video and audio.

As explained above, according to the present invention, (1) the oscillation frequency of the oscillator can be lowered to _G − _P , resulting in higher oscillation stability; (2) the interference signal _G can be controlled by controlling the frequency _P ; It is obtained by mixing the pilot signal and the oscillation signal (constant level) of frequency _G - _P , so
The level of the above signal _G is the control pilot signal _P.
Since the level of the interference signal G is proportional to the video carrier level, and since the degree of attenuation of the transmission line is considered to be almost the same for both _V and _P , the level of the interfering signal _G is proportional to the video carrier level, and each branch line It is possible to maintain an appropriate level at all times depending on the level of the video carrier wave.

(3) Since the frequency-converted signal of the modulated control pilot signal is used as the jamming signal, this jamming signal is also modulated. Benefits include greater interference effects and improved scrambling.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the general configuration of a pay television system, FIG. 2 is a block diagram showing the configuration of a conventional scrambling device, and FIG. 3 is a block diagram showing the configuration of a scrambling device according to the present invention. FIG. 4 is a spectrum diagram of the transmitted signal. 1...Head end, 2...Modulator, 3...
Control signal generator, 4...mixer, 5...distributor,
6a to 6d... Turnout, 7a to 7d... Scramble device, 8a to 8d... Television receiver, 9...
Input, 10... Output, 11... Duplexer, 12...
First filter, 13... Demodulator, 14... Controller, 15... Oscillator, 16... Mixer, 17...
Frequency converter, 18...second filter.

Claims (1)

[Scope of utility model registration request] A pay television system in which the scrambling operation of a scrambling device on a branch line branching out to each subscriber is controlled by a control signal related to contract information transmitted together with a broadcast signal from the transmitting side.
In the system, the scrambling device separates a control signal and a broadcast signal of frequency _P superimposed on the signal from the received signal on the branch line, and outputs the splitter, and a first filter that passes the control signal. , a demodulator that demodulates the signal that has passed through the filter, a controller that controls scrambling on and off according to the demodulated signal, and under the control of the controller, the frequency of the interfering signal is set to _G , and _G - _P is set. an oscillator that oscillates at a frequency, a frequency converter that mixes the signal with a frequency _P that has passed through the first filter and the output of the oscillator with a frequency _G − _P , and outputs a jamming signal with a frequency _G ; A scrambling device for a pay television system, comprising: a second filter for passing through; and a mixer for returning the output of the second filter to a branch line and mixing it with the broadcast signal.