JPS632482A - Tv signal transmitting/receiving system - Google Patents

Abstract

PURPOSE:To disable the generation of a gain control signal based upon only the AM detection of a sound signal and to prevent personal transmission/ reception from being tapped by a third person by discriminating the compressed portions of horizontal and vertical synchronizing signals by timing pulse width. CONSTITUTION:A sound signal B out of a TV signal supplied to an input terminal 1 is frequency-separated from a video signal A and detected by an AM detecting circuit 4. The output C of the circuit 4 is supplied to a pulse width modulating circuit 5, a pulse width detecting circuit 6 and a reset terminal R of an FF 7. An OR gate 8 finds out OR operation between the output D of the circuit 5 and the output E of the FF 7 and outputs a signal F. Since the signal F is turned to the H level at the time portions T1, T2 of the signal A, the signal A is supplied to a gain variable amplifier 2 to increase the gain only for the H level period. Consequently, the TV signal existing before the level compression can be restored from the signal obtained from the terminal 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to a TV signal transmission and reception system used for transmission and reception of pay TV broadcasting and the like using CATV and DBS.

(2) Prior Art Conventionally, the circuits shown in FIGS. 4 and 5 and the signals shown in FIG. 6 have been used to prevent unauthorized viewing by third parties in paid TV broadcasts and the like.

FIG. 4 shows a transmitter in a TV signal transmission and reception system.

In FIG. 4, input terminals 11 and 12 are supplied with a video signal and an FM audio signal to be transmitted, respectively. A horizontal synchronization signal and a vertical synchronization signal are extracted from the video signal by a synchronization separation circuit 14 and supplied to a timing pulse generation circuit 15 . The timing pulse generation circuit 15 is
A signal corresponding to the signal shown in FIG. 6(C), that is, a timing pulse signal C that becomes high level in each synchronization signal section.
is generated and supplied to the synchronization suppression circuit 13 and the imaging unit modulation generation circuit 16.

The synchronization suppression circuit 13 outputs a synchronization signal portion of the video signal supplied to the input terminal 11, that is, a horizontal synchronization signal at a time T1 and a horizontal synchronization signal at a time T2 as shown in FIG. 6(a). The vertical synchronizing signals are each compressed in level by about 6 dB to 10 dB and supplied to the adder circuit 18.

Further, the amplitude modulation generation circuit 16 uses the timing pulse signal C supplied from the timing pulse generation port 'j315 as a reference to generate a signal whose amplitude is large in the synchronization signal portion of the FM audio signal supplied to the input terminal 12. 6. Create signal B shown in Figure (b). The outputs of the synchronization suppression circuit 13 and the S-width modulation generation circuit 16, that is, the video signal A and the audio signal B, are added in an adder circuit 18 and output from an output terminal 19, and then modulated according to the propagation path. A transmission output is performed.

FIG. 5 shows a receiver in a TV signal transmission and reception system.

In FIG. 5, an input terminal 1 is supplied with a TV signal including a video signal A and an audio signal B sent from the transmitter described in FIG. In the video signal A, as shown in FIG. 6(a), the level of the horizontal synchronizing signal at time TI and the vertical synchronizing signal at time T2 are compressed by about 6 dB to 10 dB, respectively. Furthermore, the audio signal B is amplitude-modulated by a timing pulse whose level changes to high level at the point where the video signal is level-compressed (6th
Signal B) in figure (b).

The audio signal B is frequency-separated from the video signal A by the audio signal filter 3 and detected by the AM detection circuit 4 (signal C in FIG. 6(c)). The pulse width of the output signal C of the AM detection circuit 4 is adjusted by the pulse width adjustment circuit 5, so that the output signal C of the AM detection circuit 4 becomes high level corresponding to the portion where the horizontal synchronization signal and the vertical synchronization signal of the video signal A are level-compressed. Then, a signal with an expanded pulse width is created. The pulse width adjustment circuit 5 includes, for example, a time constant circuit and a level slicer.

The signal R, which is the output of the pulse width adjustment circuit 5, becomes high level corresponding to the location where the horizontal synchronization signal and vertical synchronization signal of the signal A are level-compressed, so it is supplied to the variable gain amplifier 2 to adjust the gain. By controlling the
As shown by the broken line in , the TV signal is restored to the original TV signal before being scrambled.

In this way, TV signals are transmitted and received.

(3) Problems to be Solved by the Invention The conventional TV signal transmitting and receiving system shown in FIGS. 4 and 5 has advantages such as a simple circuit, but on the other hand, it has problems as shown in FIG. 6(b). Since the gain control signal shown in FIG. 6(d) can be easily created by simply performing AM detection on the signal shown in FIG. The problem is that you can't get it.

(4) Means for solving the problems The present invention has been made in view of the above points, and aims to effectively prevent unauthorized viewing with a simple circuit configuration.
To achieve this purpose, we have developed a TV signal transmitter that compresses the level of the horizontal and vertical synchronization signals of a video signal and modulates the amplitude of the TV audio signal with a timing pulse that indicates the location where the level has been compressed. @ A TV signal receiver having a pulse width detection circuit that detects the pulse width of the timing pulse obtained by demodulation is provided, and the horizontal synchronization signal is compressed by the pulse width of the timing pulse, and the vertical synchronization signal is compressed. It is configured to identify.

(5) Effect With this configuration, instead of using the pulse width of the timing pulse as it is to indicate the position where the level has been compressed, the position where the level has been compressed is identified by the type of pulse width. Merely performing AM detection on the signal shown in b) does not allow descrambling.

(6) Examples Hereinafter, the present invention will be explained based on the drawings.

FIGS. 1 and 2 are block diagrams showing an embodiment of a TV signal transmitting and receiving system according to the present invention.

FIG. 1 shows a transmitter in a TV signal transmission and reception system.

In FIG. 1, input terminals 11 and 12 are supplied with a video signal and an FM audio signal to be transmitted, respectively. A horizontal synchronization signal and a vertical synchronization signal are extracted from the video signal by a synchronization separation circuit 14 and supplied to a timing pulse generation circuit 15 . The timing pulse generation circuit 15 is
A timing pulse signal that becomes high level in each synchronization signal section is generated, and the synchronization suppression circuit 13 and pulse width converter 17
supply to.

In the synchronization suppression circuit 13, the synchronization signal part of the video signal supplied to the input terminal 11, that is, as shown in FIG. The signals are level-compressed by about 6 dB to 10 dB and then supplied to the adder circuit 18. Further, the pulse width converter 17 uses the timing pulse signal supplied from the timing pulse generation circuit 15 as a reference, and the pulse width converter 17 has a pulse width of 1. A pulse signal C with a pulse width t2 is created in the vertical synchronization signal portion (6th
Signal C) shown in Figure (C). This pulse signal C is supplied to an amplitude modulation generation circuit 16.

The amplitude modulation generation circuit 16 amplitude modulates the FM audio signal supplied to the input terminal 12 in accordance with the pulse signal supplied from the pulse width converter 17, so that the amplitude is large in the horizontal synchronization signal and vertical synchronization signal portions. The signal B shown in FIG. 3(b) becomes
make. The outputs of the synchronization suppression circuit 13 and the amplitude modulation generation circuit 16, that is, the video signal A and the audio signal B, are added in an adder circuit 18 and output from an output terminal 19, and then modulated and transmitted according to the propagation path. Output is performed.

FIG. 2 shows a receiver in a TV signal transmission and reception system. In FIG. 2, a TV signal including a video signal A and an audio signal B is supplied to an input terminal 1. In the video signal A, as shown in FIG. 3(a), the level of the horizontal synchronizing signal at time T1 and the vertical synchronizing signal at time T2 are compressed by about 6 dB to 10 dB.

The audio signal B is amplitude-modulated by a timing pulse, and this timing pulse continues at a high level for a pulse width t1 from the position where level compression of the horizontal synchronization signal starts, as shown in FIG. 3(b). In addition, the pulse continues to be at a high level for a pulse width t3 from the position where the level compression of the vertical synchronizing signal is started. Note that in signal B, only the last equivalent pulse included in the vertical synchronization signal is used for modulation as signal b4, but other equivalent pulses included in the vertical synchronization signal are not used.

Of the TV signals supplied to the input terminal 1, the audio signal B is frequency-separated from the video signal A by the audio signal filter 3 and detected by the AM detection circuit 4 (signal C in FIG. 3(c)). The signal C, which is the output of the AM detection circuit 4, is sent to a pulse width adjustment circuit 5, a pulse width detection circuit 6, and a flip-flop 7.
is supplied to the reset terminal R of.

, the pulse width adjustment circuit 5 sets the pulse width t1 to the pulse width TI
It is a circuit that expands to , and is composed of, for example, a time constant circuit and a level slicer. It can also be configured by a mono-multivibrator with a reversal time of T1. The output of the pulse width adjustment circuit 5 is supplied to the input terminal of the OR gate 80 after the pulse width is expanded as shown in the signal shown in FIG. 3(d).

The pulse width detection circuit 6 is a circuit that determines whether the pulse width of the signal C is a pulse width t1 or a pulse @t3. For example, the pulse width detection circuit 6 is a circuit that determines whether the pulse width of the signal C is a pulse width t1 or a pulse @t3. It is composed of an AND gate that performs the logical product of the output of the signal C and the signal C. The pulse width detection circuit 6 receives the signal Ca (FIG. 3(C)
) outputs an output signal that becomes high level when time t1 has elapsed since the rise of the signal. The output of this pulse width detection circuit 6 is supplied to a set terminal S of a flip-flop 7.

The flip-flop 7 is an R5 type flip-flop that is set by the rise of the output of the pulse width detection circuit 6 and reset by the rise of the signal C which is the output of the AM detection circuit 4. The output Q of the flip-flop 7 becomes a signal E shown in FIG. 2(e), and is supplied to the input terminal of the OR gate 8.

The OR gate 8 logically ORs the signal R which is the output of the pulse width adjustment circuit 5 and the signal E which is the output of the flip-flop 7. The output becomes signal F shown in FIG. 3(e). This signal F is a signal that becomes high level at time T1 and time T2 of signal A, so this signal F is supplied to the variable gain amplifier 2, and the gain is increased by the time when the signal A becomes high level. . As a result, input terminal 1
The TV signal before being level compressed (scrambled) can be restored (descrambled) from the signal supplied to the. The restored TV signal is supplied from the output terminal 9 to an external TV receiver or monitor.

Note that the pulse width T4 of the signal F is more accurately shorter than the time T2. Therefore, the signal A is outputted from the variable gain amplifier 2 in a level-compressed state due to the short length. However, the period T2 is within the vertical synchronization signal and is out of sight on the TV screen, and the synchronization signal is accurately restored ( Since the output terminal 9 is descrambled), it does not affect the screen on the TV receiver or monitor connected to the output terminal 9.

Although the present invention has been described above based on embodiments, the following modifications are also possible according to the technical idea of the present invention.

For example, instead of the flip-flop 7, a monomultivibrator can be used which is triggered by the output of the pulse width detection port H6 and has an inversion time T2. In this case, signal b4 (the last equivalent pulse in the vertical synchronization signal)
It is possible to generate the pulse width T2 as a gain control signal without using .

(7) Effects of the Invention As explained above, the present invention provides a TV signal in which the horizontal synchronization signal and vertical synchronization signal of a video signal are level-compressed, and the TV audio signal is amplitude-modulated with a timing pulse indicating the location where the level has been compressed. A point where a transmitter and a TV signal receiver having a pulse width detection circuit that detects the pulse width of a timing pulse obtained by demodulating a TV audio signal are provided, and the horizontal synchronization signal is compressed by the pulse width of the timing pulse. Since the configuration is configured to identify the location where the vertical synchronization signal is compressed and the location where the vertical synchronization signal is compressed, the gain control signal cannot be obtained by simply performing AM detection on the audio signal, making it difficult for third parties to steal the signal. It becomes possible to effectively prevent viewing.

[Brief explanation of drawings]

1 and 2 are block diagrams showing one embodiment of the TV signal transmitting and receiving system according to the present invention, FIG. 3 is a waveform diagram explaining the operation of the circuit shown in FIGS. 1 and 2, and FIGS. FIG. 5 is a block diagram showing a conventional TV signal transmission/reception system, and FIG. 6 is a waveform diagram illustrating the operation of the circuit shown in FIGS. 4 and 5. 2... Variable gain amplifier 4... AM detection circuit 5... Pulse @ adjustment circuit 6... Pulse width detection circuit 7... Flip-flop 8... OR gate 13... Synchronization suppression circuit 15. ...Timing pulse generation circuit 16...Amplitude modulation generation circuit 17 Φψsha pulse width converter patent applicant NEC Home Electronics Co., Ltd.

Claims (1)

[Claims] A TV signal transmitter that level-compresses a horizontal synchronization signal and a vertical synchronization signal of a video signal and amplitude-modulates a TV audio signal with a timing pulse indicating the location where the level is compressed; and a TV audio signal obtained by amplitude demodulating the TV audio signal. and a TV signal receiver having a pulse width detection circuit that detects the pulse width of the timing pulse, and identifies a location where the horizontal synchronization signal is compressed and a location where the vertical synchronization signal is compressed based on the pulse width of the timing pulse. A TV signal transmitting/receiving system characterized by: