JPH0560717B2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to viewing control of pay channels in a CATV system, and in particular, in the distribution system of CATV signals on the subscriber side, interference waves are mixed into the frequency band of channels that are not allowed to be viewed. , relates to a method of scrambling a specific channel.

(Prior Art) In conventional CATV systems, various methods and devices have been implemented to ensure fair CATV operations regarding the provision of pay programs to subscribers. The paid program referred to here refers to the viewing of a specific channel based on a basic contract and a contract for each individual subscriber that is higher than the basic service based on the basic contract.

The simplest configuration to prevent non-subscribers from watching paid programs in secret is to install a CATV frequency converter in the subscriber's home, convert the VHF channel so that it can be viewed on a TV receiver, and then connect the coaxial cable on the subscriber's side. In this method, a band removal filter is installed at the cable lead-in section (hereinafter referred to as the tap section), and viewing of channels other than those subscribed to is prohibited.

The disadvantage of this method is that band removal filters (hereinafter referred to as traps) may be required due to changes in contract details or subscribers.
It is necessary to install and remove traps, which significantly increases operating costs and limits the number of traps that can be installed, which naturally imposes restrictions on these paid channels.

Furthermore, addressable home terminals have been put into practical use in order to eliminate these drawbacks. This configuration will be explained below.

The subscriber's home equipment is polled by the program broadcasting station (hereinafter referred to as the head end) and compares the polling address with an address previously stored in the home equipment, and when they match, captures the data.
Viewing is controlled via data communication from the head end, and includes a demodulator and a microcomputer to read the data.
In addition, paid programs are scrambled (destroyed to an unviewable state) at the head end in advance.
A method is being used to descramble (restore destroyed images) channels that are allowed for data communication viewing at the subscriber's premises.

In this commonly used scramble channel, the horizontal synchronizing signal of the TV signal is removed in advance at the head end according to a predetermined rule, making it difficult to perform synchronized reproduction on the TV receiver side. Therefore, on the descrambler side of the home equipment,
It is necessary to restore these synchronization signals, and the subscriber premises terminal also requires these descramblers and a demodulator for receiving data to control them.

(Disadvantages of the Prior Art) The prior art system for preventing eavesdropping on paid programs requires a descrambler and a data communication demodulator in the subscriber's premises terminal, which increases the cost of the terminal. In addition, the image quality deteriorates because the scrambled images are descrambled, and furthermore, if the subscriber intentionally modifies the terminal device in the subscriber's home, the subscriber who is not authorized to view the paid program may be able to watch it. There was a drawback that it became possible to watch.

In addition, in view of the above circumstances, we are preventing eavesdropping on paid programs by generating interfering signals on paid channels in a time-divisional manner at the subscriber cable outlet and selectively injecting these interfering signals to unsubscribed channels. I have something to do.

The method of mixing interference waves into a CATV pay channel as described above and scrambling the channel to control viewing is a well-known technology, and at present, it is rather a method of generating interference waves and a method that is more suitable for system operation. Providing products with characteristics has become a technical challenge.

The methods that have been proposed or realized so far that time-divisionally inject jamming signals into the above-mentioned paid channels include voltage controlled oscillators (hereinafter referred to as
A system that uses one or more pairs of VCO (hereinafter referred to as VCO) and phase-locked loop (hereinafter referred to as PLL) to generate interference waves over the entire CATV band, and mixes interference signals into specific channels intermittently and in a time-division manner. is common.

The scrambling effect of interference waves acts on the visual signal fv of the TV signal, interfering with the synchronized playback of the TV receiver and making reception difficult. Precision is required. However, when affecting and interfering with the horizontal synchronization and vertical synchronization reproduction systems of TV receivers, the method of using one interference wave generator intermittently and time-divisionally across multiple channels does not The pull-in and synchronization times cannot be ignored, and appear as scrambling effects and constraints on the number of channels that can be controlled.

Furthermore, in such a scrambling system, in order to further enhance the jamming effect, it is desirable to apply a jamming signal that is 5 to 10 dB larger than the visual signal amplitude of each channel. It is very difficult to uniformly manage all channels, and solving this problem is a major problem.

This is because the downstream video signal in CATV is
It exists over a wide band of 50 to 500MHz,
Furthermore, the CATV signal line (coaxial cable) that transmits this signal has frequency characteristics, and generally has the problem that the RF level is more attenuated in higher frequency bands than in lower frequency bands.

Furthermore, the amount of attenuation of the CATV signal line varies depending on the distance, and the distances between the CATV center and each terminal vary.

As can be understood from the above explanation, it is expected that it will be extremely difficult to individually apply jamming signals at the optimal level as described above to all pay programs on each terminal, and there are specific methods to overcome this problem. A method is desired.

(Object of the invention) In view of the above circumstances, the present invention has been developed to provide a compact and economical
The purpose of the present invention is to provide a viewing control device using a CATV pay channel viewing control signal distribution system. Specifically, CATV from CATV center
The purpose is to maintain the interference wave signal applied to the signal for each channel at a constant level with respect to the signal level of each channel of this CATV signal.

(Structure of the Invention) Examples of the present invention will be described below with reference to the drawings.

Figure 1 shows a tree-type CATV signal distribution device.
This example shows a case where it is realized by a CATV system. In the figure, 11 is a source for transmitting video and audio signals at predetermined frequency intervals, and 12 is a polling device for controlling whether or not viewing is permitted based on contract information of frequency-multiplexed CATV subscribers. 13 is a modem for modulating polling data into an RF signal, and 14 is a coupler.
15 is a main amplifier, 16 is a branch amplifier, 17 is an extension amplifier, 19a and 19b each indicate a CATV signal distribution device according to the present invention, and 20a to 20j
21a and 21 indicate the subscriber side drop-in lines, respectively.
b indicates a subscriber's home, 22a and 22b a CATV converter, and 23a and 23b a TV set.

FIG. 2 is a diagram for explaining a CATV signal distribution system which is an embodiment of the present invention.
The configurations of 9a and 19b are shown. 24a, 2 in the figure
4b is a coaxial cable and a connector connected to a feeder line; 25 and 26 are branchers for passing and branching CATV signals; and 27 is a demodulator for data communication carried out by a polling method from a broadcasting center. 28 is a microcomputer, 29 is a ROM for storing polling addresses corresponding to subscribers and frequency selection information for generating jamming signals, and 30 is a RAM for storing contract information for viewing paid channels for each subscriber. , 31
Reference numerals a and 31b indicate address data buses connected to the microcomputer, respectively. 40 in the diagram
is a jamming signal generation stage that generates a jamming signal, and 39 is a stage that generates a voltage corresponding to the oscillation frequency.
It shows a D/A converter for feeding to VCO40,
Reference numeral 38 indicates a data bus for providing voltage information corresponding to the frequency from the microcomputer 28. 37 indicates a frequency divider for dividing the oscillation frequency of the jamming signal generation stage 40 to 1/M;
It shows a prescaler that has the function of frequency division and converting the RF level to logic level. 36 indicates its output, 35 is a binary n-bit counter, and the microcomputer 28, whose output is indicated by 34.
is input to. Signals 32 and 33 are used by the microcomputer 28 to control the counter 35, 32 is for resetting the counter, and 33 is for controlling counter enable/disable of the counter. 42 in the figure indicates the jamming signal 41 generated in the jamming signal generation stage 40.
A distributor for distributing to the input side of the RF switches (RFSWs 43a to 43f) is shown. 44a~
Reference numeral 44f indicates a control signal line for controlling the opening and closing of the RFSWs 43a to 43f, and the opening and closing are controlled according to the subscriber's contract conditions upon receiving commands from the microcomputer 28, and the oscillation signal from the VCO is transmitted according to the opening and closing of the RFSWs 43a to 43f. supply. 45a
45f indicates a branching device (directional coupler), and the frequency spectrum of the output from the RF switches 43a to 43f produces a jamming signal with a sharp pattern in contrast to the CATV signal that is the output of the branching device indicated by 47 in the figure. The signals are combined and output to subscriber side output terminals 48a to 48f.

In other words, the scrambling method using the jamming method acts on the synchronous playback system and AGC system of the subscriber's TV receiver as mentioned above, and particularly disturbs the synchronous playback, but as is well known, the TV receiver has a noise removal circuit. After video detection, noise above a predetermined level relative to the synchronization signal level is removed.

Therefore, in order for the jamming signal applied to the CATV signal to work effectively, it is necessary to
It is desirable to always maintain a constant amplitude with the CATV signal. Experiments have shown that it is most effective when the jamming signal amplitude is 5 to 10 dB larger than the visual signal amplitude of the channel. Furthermore, the CATV signal amplitude fluctuates depending on the characteristics of the amplifier in the transmission system and the frequency characteristics of the coaxial cable, and the jamming signal level also fluctuates to follow these fluctuations, so it is desirable to always maintain the optimum level.

For this purpose, the jamming signal generation stage 40 has the following configuration.

40A is a low pass filter (hereinafter referred to as LPF), 40B is a mixer (hereinafter referred to as 1st mixer) that mixes the output of VCO 40H controlled by the D/A converter 39 to the CATV signal obtained from the splitter 47; The output frequency of is always controlled so that the mixer output of the channel is at intermediate frequency _L.
In other words, if the VCO output is j and the frequency of the channel is v, then j + v = _L (intermediate frequency)
It is controlled so that 40C, 40E
indicates an intermediate frequency band filter, and 40D indicates an intermediate frequency amplifier. 40F indicates the second mixer (hereinafter referred to as 2nd mixer), _L −j, _L +j
Output and use a 40G bandpass filter to obtain v (= _L − j)
Extract. Here, the extracted frequency v is 1st
The frequency v of the channel that is input to the mixer along with other CATV signals is the same, but its phase changes as it passes through this 1ST mixer, intermediate frequency amplifier, and 2nd mixer.
This frequency v, which is superimposed at the directional coupler via the RF switch, makes it impossible to view and listen on the subscriber terminal. In this way, the TV signal of the channel is applied as a jamming signal at the amplification factor of the intermediate frequency amplifier 40D. Therefore, the jamming signal amplitude always maintains a constant level ratio with respect to the channel amplitude. At the same time, a jamming signal is applied not only to v but also to the TV audio signal a, giving a scrambling effect to the video and audio.

FIG. 3 explains an embodiment of the VCO control section. This figure is a diagram illustrating how the present invention can achieve high speed (ie, how effective a jamming signal can be generated) and an economical device. In the figure, the same symbols as in FIG. 2 indicate the same functions.

In the figure, 39a, 39b, and 39c indicate D/A converter sections for VCO control. 39a _-1 to 39a _-4 represent CMOS logic gates, 39a _-5 to 39a _-9 represent resistors, and 39a _-10 represent an operational amplifier, constituting a simple D/A converter. The same applies to 39b, and 39b _-1 to 39b _-4 are
CMOS logic gates, 39b _-5 to 39b _-9 are resistors,
39b _-10 is an operational amplifier, and 39b _-11 is a resistive attenuator. The resistance attenuator 39b _-11 connects the D/A converters 39a and 39b to a Vn bit D/A.
If it is a converter, the D/A converter 39a
If the value is determined so that 1/2 of the LSB is equal to the MSB of the D/A converter 39b, a simple 2n-bit D/A converter can be realized. 39c is 39
An adder is shown that adds the outputs of a and 39b, and its output is the output of a 2n-but D/A converter.

FIG. 4 shows the timing of each part to explain the jamming signal generation method according to the present invention. In the figure, 50 indicates the voltage of the D/A converter 39 that controls the jamming signal generation stage 40, the horizontal axis indicates time, and the vertical axis indicates the VCO applied voltage or the oscillation frequency of the VCO. 50
The scramble channel due to jamming is i
This shows that a jamming signal is applied to each channel for a period of Tφ, and that the period is _T1 . The figure also shows the frequency correction period T2a,
This shows that T2b, periods T _3a and T _3b are inserted. 51 shows in detail the frequency correction periods indicated by T _3a and T _3b . Reference numeral 52 indicates the control state of the counter 35 by the microcomputer in FIG. To explain according to 51 in the figure, tc ₁ , tc ₂ , tc ₃ , and tc ₄ indicate the counting times of the frequency counter 35, and t _R1 , t _R2 , and t _R3 indicate the reading times of the count results by the microcomputer, respectively. , ts1, ts2, and ts3 each indicate the reset time of the counter, and _tD1 , _tD2 , and _tD3 each indicate the D/A converter conversion time.

Reference numerals 54, 55, 56, and 57 indicate opening/closing control timings of the RF switches 43a to 43f for the subscriber side, respectively, and in this figure, "H" indicates the switch is closed, and "L" indicates the switch is open. Therefore, for the subscriber to whom the jamming signal is applied at timing 54, each of the channels ₁ , ₂ , ₄ , and i is scrubbed with the jamming signal, and for the subscriber to whom the jamming signal is applied at timing 55, the images of channels ₁ and ₃ are will be scrambled.

FIG. 5 is a flowchart for performing frequency correction using a microcomputer, which is a feature of the present invention.

FIG. 6 is a memory map of the ROM 29 and RAM 30 for explaining the control method based on the contract details of each subscriber by the microcomputer according to the present invention.

(Operation and effects of the invention) The operation of the present invention will be explained below based on the drawings.

First of all, Figure 2 shows 19a and 19b in Figure 1.
This shows the internal configuration of the CATV signal distributor.
This device uses data communication from the head end in a polling format, and when the address stored in the device and the polling address match, the device receives the data and sends the subscriber to the CATV pay channel according to the pre-assigned address. Receive viewing permission information. Data communication signals are generally
Modulated by FSK (Frequency Shift Keying)
The frequency is superimposed on the vacant frequency band of the CATV signal near 100MHz and sent out. 27 indicates its demodulator. When the pre-stored address matches the polled address, the microcomputer reads the data and stores the subscriber's contract information in the RAM 30. used here
Whether the RAM 30 is a mechanical memory element such as a switch or a semiconductor memory device, it is not essential to the present invention. A in Figure 6 is ADR ₁ ~
It is illustrated that the address of each subscriber is stored as ADRi. B in FIG. 6 shows that viewing permission/disapproval channels are stored for each subscriber using polling information as CH E/D ₁ to E/Di.

This device also stores frequency array information in the ROM.
It has for CATV frequency array. An example is shown in A of FIG. 6 as ₁ count to j count.
The microcomputer extracts any of the frequency array information ₁ to i corresponding to the viewing control channel (paid program) from the polling data, and outputs the D/
Output to A converter 39. The output of the D/A converter is switched periodically as shown at 50 in FIG. 4, and jamming signals for all pay channels are generated in a time-division manner. The microcomputer 28
Viewing control data CH E/D ₁ ~ RFSW43a ~ according to E/Di written in RAM30
Controls the opening and closing of 43f. To explain according to the figure, the RF switch 43a is connected to the subscribers 54, 4.
3b is subscriber 55, 43c is subscriber 56, 43f
corresponds to subscriber 57, and when the output of D/A converter 39 oscillates at the jamming frequency of VCO frequency ₁ , subscribers 54, 55, and 57 are prohibited from viewing the corresponding channel, and the
RF switches 43a, 43b, 43f are closed and Tφ
A period jamming signal is superimposed on the frequency spectrum of the channel. In the next Tφ period,
The channel corresponding to ₂ is blocked and becomes 5 in Figure 4.
RF switches 43a and 43f indicate that subscribers 4 and 57 are prohibited from viewing.
indicates that it is closed. 43a-43f
The RF switch normally has the function of turning on/off the CATV band 50~450MHz signal at high speed.
Analog switches consisting of FETs, transistors, pin diodes, etc. are used.

The jamming signal generation period T1 in Figure 4 is normally
It is taken as an integral multiple of the horizontal synchronization period of the TV signal.

As can be easily understood from these explanations, the shorter the jamming period T ₁ is, the better the jamming effect is, and with the same scrambling effect, the number of payable channels that can be controlled increases. T ₁
To shorten the jamming signal generation time Tφ
It is necessary to shorten the switching time of the RF switch and the response time of the VCO and D/A converter.

Next, the frequency control method of the VCO that generates the jamming signal, which is the most significant feature of the present invention, will be explained. As mentioned above, the D/A converter voltage for jamming signal generation is performed by outputting the data written in the ROM 29 to the D/A converter 39, but the frequency control of the jamming signal generation stage 40 is normally controlled by the voltage of the varistor diode. - It is carried out by utilizing capacitance characteristics, and its value differs from one varistor diode to another, and it also changes significantly depending on the ambient temperature, so it is not suitable for practical use by itself. Further, the jamming effect appears most when the jamming frequency is within ±500k with respect to the frequency of v of the TV signal.

The present invention solves these problems. That is, (1) In the initial state of power-on of this device, read the frequency array information ₁ count to j count in the ROM, and convert the data conversion coefficient D/A of the D/A converter.
It is multiplied by Acon (Fig. 6A) and output to the D/A converter.

(2) Next, the counter 35 is enabled by the control signal 33 and starts counting.

(3) After operating the counter 35 for a specified time, the counter 35 is stopped and the oscillation frequency of the VCO is measured by determining the number of counts per unit time. It is necessary to accurately determine the specified time and control the start and stop of the counter.
A time signal may be given from outside the microcomputer, but it may also be determined from instructions and execution steps inside the microcomputer.

(4) Frequency 1count~icount stored in ROM
and the measurement frequency 0 (hereinafter simply referred to as 0) is determined as the frequency difference.

(5) Increase or decrease the data of the D/A converter that was output earlier and repeat steps (1) to (4).
Repeat until the value of kcount-0 (k is an arbitrary channel) falls within a predetermined error.

(6) Perform the above steps for all channels designated as paid channels, and finally
A converter 39 data onto RAM 30
Store as CMP1M to CMPkL. In the figure,
M, L are 39a, 39b, D/ in Fig. 3.
It means CMPiM and CMPiL of the D/A converter corresponding to the upper digit side and lower digit side of the A converter.

The above is the correction of the data of the D/A converter in the initial state, and during the actual viewing control of paid programs, the CMP1M~
It is necessary to correct the CMPkL value. The T _2a and T _2b periods in Figure 4, 50, show this, and 51
shows this details. For example, once every 60 minutes, 10
When performing channel jamming channel correction, correction is performed once every 6 minutes. If the correction is performed within several hundred milliseconds, it will hardly affect the scrambling effect.

The actual operation will be illustrated according to FIG. 39
A and 39b realize a 16-bit D/A converter 39, and the prescaler 37 is divided into 1/64 by 64.
The counter 35 is an 8-bit shift register, and a carry generated at the time of overflow is used as an interrupt signal to the microcomputer 28. The microcomputer 28 performs a count using internally set software for each interrupt. It is assumed that the jamming signal generation stage 40 once oscillates in the UHF band to cover 50 to 450 MHz and converts it down. As an example (50~450M
Hz) +600MHz and convert this to {(50~450)+600}
Assume that it is down-converted to -600. Therefore, the prescaler 37 input frequency is 650 to 1050MHz.
The counter input is (10.156 to 16.406) MHz
becomes. Also, since the carry of the counter 35 occurs every time the 8-bit shift register overflows, it becomes 1/256 of the input of the counter 35.
(0.0397 to 0.064) MHz. If the counting time of the counter 35 is 1 msec, the number of counts is (10106 to 16406), which is an accuracy of 13 bits or more, exceeding 2 to the 13th power (8192), and if the counting time is 2 msec, the accuracy is 14 bits or more. This means that the frequency can be measured with an accuracy of .

Here, since counting the output of the prescaler 37 as it is causes a heavy burden on the microcomputer 28, an 8-bit shift register is used. Since the carry of the shift register 35 has a frequency that is sufficiently processable for the microcomputer 28, it is counted by software and added to the value remaining in the shift register 35 after the count ends to obtain the frequency.
That is, the value counted by the microcomputer 28 using software is set to a, and the shift register 35
If the value remaining in the (counter) is b, the total number counted in the counting time c is (a x 256 +
b) ke, and its frequency is {(a×256+b)×
64/c}Hz.

Returning to FIG. 3, the actual operation will be explained. 3 in the diagram
9a _-1 ~39a _-4 and 39b _-1 ~39b _-4 , 39a _-5 ~
39a _-9 and 39b _-5 ~ 39b _-9 , 39a _-10 and 39b _-10
are the same and each constitutes an 8-bit D/A. 3
The resistance value of 9a _-5 is R, and 39a _-6 is 2 x R39
A simple 8-bit D/A converter is realized when a _-7 has a relationship of 2 ² ×R and 39a _-8 has a relationship of 2 ⁷ ×R. 39a _-9 is for determining the conversion gain and can be set arbitrarily. This D/A converter
It utilizes the current drive characteristics of CMOS gates 39a _-1 to 39a _-4 , and logic levels "L" and "H" are shunted by 39a _-5 to 8 and 39a _-9 , and the current-voltage conversion calculation is performed. It is converted into a voltage by amplifier 39a _-10 . 39b is the same, but resistive attenuator 39b _-11
is 39b _-10 highest digit output is 1/ of 39a _-10 lowest digit output
It is set up so that it becomes 2.

With the above configuration, it is easy to see that a 16-bit D/A converter can be realized simply and at a very low cost.

FIG. 5 is a flowchart of a routine for calculating D/A converter frequency control data in an initial state and correcting it during operation. This flow is a process for one jamming channel, and it is necessary to process all jamming channels.

Step 1 is to determine whether this device is in its initial state. Step 2 is skipped unless it is used for the first time or is forced to initialize during system maintenance.

In step 2, the correction value index "CMP" stored in the RAM 30 is initialized.
That is, set it to 0.

Step 3 and subsequent steps are repeated several times, but the first time is a rough adjustment, so counting is performed to correct the upper bits.

In step 3, the information stored in ROM29 is
Multiply the count value by the conversion count indicated by the D/A converter to obtain the value actually output to the D/A converter, and then add "CMP" of RAM30 to obtain the data of the D/A converter for channel i. Create a value to be written to the D/A converter as “CMP”<CHi>.

In step 4, the value created in step 3 is converted to D/A.
Output to converter.

In step 5, the D/A converter and VCO4
Waiting for time until 0H settles down.

In step 6, the count 35 is initialized, and in step 7, counting is started.

In step 8, after counting for a predetermined period of time, the count for correcting the upper bits in the case of coarse adjustment goes to step 10, but when counting for correcting the lower bits in the case of fine adjustment, the timer is counted again to improve accuracy. wait. This determination is made in step 9. In this example, 0.5 msec is sufficient for step 8, and D/A for fine adjustment in step 9 is sufficient.
Converter correction is 2 to the 8th power 256 x 0.5 =
Requires 128msec.

At step 10, counting ends.

In step 11, the deviation ΔF between this count value and the count value stored in the ROM 29 is determined, and in step 12 it is determined whether the deviation is within a predetermined value. If it is determined in step 12 that the deviation is large, the process proceeds to step 15, and if the deviation is small, the process proceeds to step 13.

In step 15, the sign of the deviation is checked, and in accordance with this, in step 16, the correction value "CMP" stored in the RAM 30 is increased or decreased. Step 13
Then, the number of times the configuration routine is passed is counted, and when the number of times of the loop parameter is 3 or less in step 14, the process proceeds to step 17, and when the number of times is 3, this routine is ended.

Step 17 is a process of changing the comparison counter value in order to improve the accuracy of the loop parameter J from the second time onwards.

The above operation is performed for all jamming channels.

The D/A converter and its frequency correction method have been illustrated above with reference to FIG.

FIG. 2 shows an embodiment in which a function is added in which the jamming carrier level always follows the level fluctuation of the CATV signal to maintain a constant level difference.

40A in the figure is the input LPF (LowPass Fielder)
Components outside the CATV signal band (50 to 450MHz) are removed, the CATV signal and VCO signal are mixed with the 40B first mixer, and only the intermediate frequency components are extracted with the 40C and 40E intermediate frequency band filters and intermediate frequency amplifiers. In other words, for the VCO oscillation frequency, the visual signal frequency of the channel to be jammed is vi, and the intermediate frequency is
If _L i and the frequency of VCO are ji, then _L i=vi+
The oscillation frequency of the VCO is controlled so that it becomes ji.

Furthermore, the intermediate frequency _L i is mixed with ji again in a 2nd mixer shown as 40F, and vi= _L i−ji components can be extracted with a bandpass filter. in this case,
The signal of the jamming CH with CATV signal amplitude is extracted with a constant gain, and not only the V signal but also the A signal can be extracted at the same time, and using this as a jamming signal will cause interference not only to the video but also to the audio. It is effective.

(Effects of the Invention) As can be understood from the above explanation, according to the present invention, the jamming signals generated in a time-division manner can be controlled at high speed, and the jamming signals that are generated in a time-division manner can be controlled at high speed. This solves the technical difficulty of controlling the amplitude of the interference waves generated in the system, especially the relative level difference of the video signal of interest. That is, the present invention can be obtained from subscriber branch lines.
It is characterized in that the frequency of the CATV signal is converted by the first and second mixers, and the phase-converted frequency-converted signal is used as the jamming signal. Therefore, the jamming signal level is CATV
By following the input level of the signal, it is possible to always add a jamming signal at a high level of about 5 to 10 dB to pay programs that exist over a wide frequency band, and obtain an extremely good scrambling effect. It has the unique effect of being able to In addition, other expected effects of the present invention will be listed.

It eliminates the transient response and delay problems of conventional AGC technology (signal extraction, detection, and gain control) and can increase speed.

Since the generation of time-division interference waves can be sped up, the number of channels that can be jammed can be increased and the jamming effect can be strengthened.

The local frequencies of the first and second mixers are
It is in the UHF band (outside the CATV band), so it does not cause interference within the CATV band, and shielding inside the device can be simplified.

The circuit configuration is simple and an economical device can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the case where the present invention is implemented in a CATV system, and FIG. 2 is a block diagram showing a first embodiment of the CATV signal distribution system of the present invention.
Fig. 2 is a block diagram showing another embodiment of the present invention, Fig. 3 is a wiring diagram for explaining the jamming signal generation method using a D/A converter and VCO, which is a feature of the present invention, and Fig. 4 is a block diagram showing another embodiment of the present invention. A timing chart to explain the jamming signal generation method, Figure 5 is a flowchart for controlling the jamming signal by the D/A converter and VCO with a microcomputer, and Figure 6 is the storage device in this device.
This is a memory map in ROM and RAM. 12... Center computer, 13... Modem, 19a, 19b... CATV signal distribution device,
21a, 21b... subscriber's house, 22a, 22b...
...CATV converter, 23a, 23b...TV set, 25, 26...brancher, 27...demodulator,
28...Microcomputer, 29...
ROM, 30...RAM, 35...Counter, 3
6... Prescaler, 39... D/A converter, 40... VCO, 42... Branch, 43a~
43f...RF switch, 45a-45f...brancher (directional coupler), 47...brancher, 48a
~48f...Subscriber side output terminal.

Claims (1)

[Claims] 1. A brancher that branches the CATV signal from the CATV signal transmission line to multiple subscriber homes, and multiple directional couplings that apply jamming signals to the subscriber side branch lines in a time-sharing manner. and an RF switch that injects or cuts off the jamming signal to each of the directional couplers, the oscillation frequency being sequentially adjusted in synchronization with the opening/closing control of the RF switch. a first mixer into which the oscillation frequency signal of the VCO is injected and into which the CATV signal is injected into the other input; and a first mixer between the first mixer and the second mixer.
Conversion loss of mixer and second mixer and the above
an intermediate frequency amplifier that amplifies and at least compensates for the difference in the level of the jamming signal with respect to the level of the CATV signal;
1. A CATV viewing control device, comprising: the second mixer which inputs a VCO oscillation frequency signal and outputs it to the RF switch.