FI75708B - VIDEO BANDSPELARE MED UPPTAGNING AV EN VIDEOTEXTSIGNAL. - Google Patents

Abstract

1. Videorecorder providing the recording of a video text signal (VT), in which the light intensity signal (Y) is recorded by frequency modulation of a picture carrier, characterized in that the received digital video text signal (VT), processed in a path (17) separated from the path (6, 7, 5) of the light intensity signal, is recorded in place of the picture carrier (B) without modulation on a carrier.

Description

, 75708

Video recorder with videotext signal recording In VHS, betamax and V 2000 VCRs, the recording of the brightness signal is performed by means of frequency carrier modulation of the image carrier from one half frame to another oblique track of the magnetic tape. It is known in connection with actual television broadcasts to transmit a digital videotext signal in addition to the actual television image during the two vertical deflection interval lines. This signal is fed in a television receiver to a signal generator which, in a short time, transmits a wideband R, G, B signal from the transmitted videotext signal. This signal is added to the FBAS signal of the CRT. In this way, it is possible to create letters on the picture tube instead of or in addition to the actual television image. The videotext signal can also be related to the actual image signal when, for example, in connection with a football match, the description for the hearing impaired is transmitted as a videotext signal. When recording such a signal on a video recorder, it is therefore desirable that, in addition to the actual television image, also a videotext signal or also only a videotext signal is recorded on the tape.

However, recording a videotext signal on commercially available VCRs is certainly not possible, because a digital videotext signal requires a bandwidth of about 3.5-4 MHz, while a recording videotape of public video recorders is only 3.0 MHz. If a videotext signal with a bandwidth of 3.0 MHz is recorded, it will no longer be possible to produce character signals without error in the videotext decoder during playback.

It is also possible, as described in EP-A 3 65 376, to record videotext signals on commercial video recorders in which the brightness signal is stored by frequency modulating the image carrier.

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However, due to the limited bandwidth of such recorders, the bit rate of the transmitted video chain signal is converted from 6.9375 Mbit / s to 2.625 Mbit / s. Extensive electronic circuits are required for this conversion, and also for playback back for conversion.

The object of the invention is to make it possible to record a video chain signal by means of conventional video recorders without having to make any significant changes to the video recorders.

The task is solved according to the invention according to the feature of claim 1. Other preferred embodiments of the invention will be apparent from the subclaims.

The invention is also characterized by the following. Recording of the video chain signal by image carrier frequency modulation, i.e. in the same way as the brightness signal, is not possible due to the limited recording bandwidth. However, a frequency-modulated image carrier recorded on a videotape with a brightness signal Y requires a bandwidth of about 6 MHz from the videotape. This bandwidth is sufficient to record the digital video chain signal directly, i.e. without carrier modulation. This is especially possible because the videotext signal is an FM signal with a constant amplitude similar to the frequency-modulated image carrier with the brightness signal, and therefore can be easily recorded in the same manner as the modulated image carrier.

The solution requires virtually no modification of the VCR. During the videotext line, it is only necessary to apply a digital videotext signal directly to the video end instead of the carrier of the modulated image, and possibly also to close the brightness signal FM modulator to reduce interference. The same procedure is followed during playback. The signal read from the videotape is then applied to the videotext decoder1 during the videotext line instead of the FM modulator.

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Fluctuations in the speed between the video head and the magnetic tape usually cause a timing error in the read signal. Such a timing error of the digital videotext signal and the corresponding line sync pulse may interfere with the decoding of the videotext signal. Therefore, during playback, the video text signal is preferably adapted to pass through a known connection during the video text decoder to compensate for timing errors. Such a circuit usually includes a delay line or electronically synchronized memory, the delay of which is controlled depending on the timing error and eliminated.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 is a block diagram of an embodiment of the invention, and Figure 2 is a timing diagram of the connection according to Figure 1.

In Fig. 1, a television radio signal which also contains a videotext signal is input from the antenna 1 to a tuner 2, which in its output provides an FBAS signal containing a videotext signal. The modulated color carrier F is processed in a bandpass filter 3 at a transmission frequency of 4.43 MHz +. 0.5 MHz and converted in a frequency converter 4 with a division constant n to a frequency of about 0.63 MHz. The modified color carrier Fm thus determined is applied to the summing circuit 5. The brightness signal Y is applied through a low-pass filter 6 having a cut-off frequency of 3 MHz to the FM modulator 7. This produces a frequency modulated image carrier B with the brightness signal Y, which is also applied to the summing circuit 5. includes a demodulated image carrier B and a color carrier Fm, applied via a switch β to the video end 9, and stored on the oblique tracks of the magnetic tape 10. With this connection, the video text signal received during the video text line would also be stored. However, the width of the folding band is too small, so that the videotext signal does not allow error-free decoding in the videotext decoder during playback.

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The recording of the videotext signal can be performed according to Fig. 2. The videotextinal VT is shifted during lines 17 and 1Θ in half-frame 1, i.e. with odd half-frames, and during lines 330 and 331 in half-frame 2, i.e. with even half-frames. The synchronization signal separation stage 11 provides a brightness signal Y pulse 12 indicating the beginning of the complete image, which is applied to a counter 13. The counter 13 counts down to lines 17, 1Θ, 330, 331 and produces a pulse 15 via a pulse shaper 14. The odd half-frames have a pulse duration of 15 according to the duration of lines 17 and 1Θ, approximately from the posterior dark period to the beginning of the anterior dark period. Thus, they are located in the line scanning time and do not temporally cover the line synchronization pulses Z or the color synchronization signal 16, whereby the recording of these signals with the image carrier B is not interrupted. During the even half images, a pulse 15 occurs as shown in Figure 2d, respectively, during lines 330 and 331.

The pulses 15 control the switch Θ and connect the video paths of the video head 9 to the output of the connection 17. In this connection, the video signals are separated and the amplitude important for recording is amplified. Correspondingly, during the duration of the pulse 15, i.e. during the scanning of the lines 17, 1Θ, 330, 331, the modulated image carrier B is not recorded, but directly the videotext signal VT via the video head 9 to the video tape 10. The pulse 15 also closes the FM modulator 7 via line 18, e.g. by switching off its operating voltage, in order to reduce the interference caused by this output signals. The pulse 15 can also switch off the summing circuit 5, in which case this does not give an output signal to the switch Θ.

During playback, the switching operates correspondingly, so that the read signal is applied to the video text decoder and not to the FM demodulator by means of a pulse 15 implemented in a corresponding manner during said lines. The video-text signal is then preferably adapted to pass through a circuit which compensates for timing errors. Such a connection is described, for example, in DE-OS 21 22 592 and DE-OS 21 29 760.