JP2850734B2 - CATV synchronous compression scramble method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV synchronous compression scramble system.

[0002]

2. Description of the Related Art In conventional synchronous compression scrambling, a part of a horizontal period and a part of a vertical period of a video signal are compressed and transmitted. FIG. 3 shows an example of a signal according to this type of scrambling method. In the scrambled signal, the terminal at the subscriber's house extracts the scramble timing superimposed on the audio signal, and expands the horizontal and vertical periods of the video signal based on the extracted scramble timing and descrambles the signal.

However, the signal scrambled by the conventional method has a problem that the level fluctuates due to the video signal and does not become a constant level because the video synchronizing signal (peak level) is compressed.

[0004]

As described above, when measuring the level of a signal scrambled by the conventional method on a transmission line, the peak of the signal is not constant, so that it is difficult to measure the signal level correctly. there were. Therefore, in order to correctly measure the level of the video signal, the scrambling is turned off and the peak of the video signal is measured.

[0005] In view of the above problems, an object of the present invention is to provide a synchronous compression scrambling method that can measure the level of a CATV transmission path.

[0006]

A CATV synchronous compression scramble system according to the present invention comprises a scramble modulating means for synchronously compressing and transmitting a CATV signal and a level measuring means.
ing. The scramble modulating means does not compress the equalizing pulses before and after the vertical period, but only compresses the vertical synchronizing pulse period, and outputs a part of the compressed signal at a normal level. And the level
The measuring means measures the normal level to obtain an image.
Measure the level of the image signal. With such a configuration, C
It can measure the level of video signal on ATV transmission line.
And it said that there was Unishi.

The scramble modulating means includes a synchronizing separator for synchronizing and detecting the horizontal and vertical periods of the video signal, a circuit for generating a scramble timing pulse based on the detection signal from the synchronizing separator, An audio IF modulator for compressing the level of the audio IF signal in a part of the horizontal and vertical periods by a timing pulse, and a video IF modulator for compressing the level of the video IF signal in a part of the horizontal and vertical periods by the scramble timing pulse And a mixer for mixing the output of the audio IF modulator and the output of the video IF modulator.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. Referring to FIG. 1, the scramble modulation unit includes a synchronization separation unit 11, a scramble timing pulse generation circuit 12, a video IF modulation unit 13, and an audio IF
It has a modulator 14 and a mixer 15. The synchronization separation unit 11 is supplied with a video signal, and outputs a horizontal signal from the video signal.
A signal detected by synchronously detecting the vertical period is output to the scramble timing pulse generation circuit 12 as a signal defining the timing of the period for compression.

[0009] Scramble timing pulse generation circuit 1
2 receives the signal separated in synchronization by the synchronization separation unit 11 and generates a scramble timing pulse based on the signal. The video IF modulating unit 13 compresses the video IF level video synchronous part with the generated scramble timing pulse. On the other hand, the audio IF modulator 14
In, a timing pulse for demodulation by a terminal device is superimposed on the audio signal. The video IF signal from the video IF modulator 13 and the audio IF from the audio IF modulator 14
After the signals are mixed by the mixer 15, the signals are frequency-converted by the frequency converter 16 into CATV channels and transmitted to the transmission path. FIG. 2 is a diagram showing the scramble timing according to the present method. By outputting a part of the vertical period at a normal level, it is possible to measure the video level in the transmission path.

[0010]

As described above, according to the present invention, by expanding a part of the compressed level in the vertical period and outputting it at the normal level, the peak level becomes the level when the scramble is not performed. Therefore, level measurement can be performed on the transmission path without turning off scrambling at the time of level measurement.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a signal waveform to which a synchronous compression scrambling method according to the present invention is applied.

FIG. 3 is a diagram showing a signal waveform according to a conventional synchronous compression scrambling method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Synchronization separation part 12 Scramble timing pulse generation circuit 13 Video IF modulation part 14 Audio IF modulation part 15 Mixer 16 Frequency conversion part

Claims (2)

(57) [Claims] 1. A CATV synchronous compression scramble system for synchronously compressing and transmitting a video signal in CATV.
Te, before and after the equalizing pulse of the vertical period of the video signal without compression, only the compressed vertical sync pulse period, a scrambling modulating means for outputting a part of a regular level, disposed CATV transmission line, Measure the normal level
Level measurement for measuring the level of the video signal by
Means for CATV synchronous compression scrambling. 2. The CATV synchronous compression scrambling method according to claim 1, wherein said scramble modulating means comprises: a synchronous separating section for separating and detecting horizontal and vertical periods of a video signal; and a detecting signal from the synchronous separating section. Circuit for generating a scramble timing pulse by using the above-mentioned scramble timing pulse;
A modulating section, and a video IF for compressing the level of the video IF signal by a part of horizontal and vertical periods by the scramble timing pulse
A CATV comprising: a modulation unit; and a mixer that mixes an output of the audio IF modulation unit and an output of the video IF modulation unit.
Synchronous compression scramble method.