DE3314782C2 - - Google Patents

Description

The invention relates to a video recorder according to the preamble of claim 1.

From Grundig Technical Information 1/1977, pages 21 to 25, it is known to use for recording color television signals the luminance signal and the color information to an FM carrier with a color carrier reduced in frequency to record on magnetic tape. When playing, it is enough the frequency of the reset color subcarrier no longer the relationship to the line frequency prescribed by the transmitter.

For video recorders based on the VHS, Betamax and V 2000 systems the luminance signal is changed by frequency modulation Image carrier with two video heads alternately on oblique tracks of a magnetic tape. Below the frequency range of the modulated image carrier becomes the frequency color carriers reduced to about 0.63 MHz are recorded. To It is also known to improve the sound quality (DE-OS 31 16 130) with the video heads one or more with sound signals record frequency-modulated sound carriers. Since in itself available recording bandwidth of about 6 MHz through the Color carrier and the image carrier is taken for such Sound carrier created an additional frequency range will. To do this, it is known to be in the frequency range of the modulated Suppress image carrier frequency ranges for the sound carrier or the upper side band of the ink carrier or the lower side band of the image carrier. Such measures can Reduce image quality.  

The invention has for its object better utilization to create the available recording bandwidth, by additional, in particular without impairing the image quality Signals such as B. record several sound signals can.

This object is achieved by the invention described in claim 1 solved. Advantageous developments of the invention are described in the subclaims.

In the solution according to the invention, the ink carrier is thus in relocated the luminance signal, and the resulting combined signal by frequency modulation of the image carrier recorded. The modulated image carrier occupied frequency range not enlarged. The so far frequency range of approximately 0.13 occupied by the ink carrier up to 1.0 MHz is used for the recording of other signals free. In this frequency range z. B. a high quality Sound signal can be recorded, especially several with sound signals frequency-modulated sound carriers or a PCM sound signal. A sound signal recorded in this way has regard to Bandwidth, signal-to-noise ratio and pitch fluctuations are essential higher quality than a sound signal that in a known manner recorded as an LF signal on a longitudinal track of the magnetic tape becomes. The invention is in all three mentioned above Video recording systems applicable. The one when shooting and separation of luminance signal necessary for playback and ink carrier is easy with this Purpose known comb filters possible. Because when playing a coupling of the color carrier frequency with the luminance signal is preserved, is a mixture of the reproduced Signals with studio signals possible. Known video recorders after the VHS or Betamax system have none during playback Coupling the color carrier frequency with the line frequency. The The invention is generally for recording a color television signal applicable, d. H. especially with VCRs  Magnetic tape and for turntables. Another advantage is that errors in playback caused by Variations in the relative speed between the video heads and the magnetic tape when converting the frequencies of color carrier and sound carrier fall out because the modulated Carrier and the mixed carrier coupled to the line frequency are subject to the same time errors.

Preferably the frequency carrier is reduced in frequency independent of its nesting in the luminance signal from the respective color saturation to the full signal peak value from Z. B. 0.7 V peak-to-peak regulated. Then at the recording itself represents the color saturation Color carrier amplitude falsified. During playback the color synchronizing signal and the synchronizing pulses in amplitude compared. With a manipulated variable obtained from this, the Amplitude of the color carrier back to that corresponding to the color saturation controlled back to the correct size. In this way the available control range can be independent of the respective Color carrier amplitude are always fully utilized, so that there is an improved signal-to-noise ratio in the playback Color signal results.

This control of the color carrier amplitude is carried out for a line with a constant control voltage because of changes the color saturation cannot be corrected in the course of a line allowed to. Then the playback would be for the back control Color carrier amplitude no identification signal available. For example becomes the amplitude at the beginning of each line the color synchronizing signal with the amplitude of the line synchronizing pulses compared. This creates a control voltage which in each case the amplitude of the color burst signal to that of Norm remains constant. This control voltage then inevitably controls also the amplitude of the color carrier during this line each time again to the one corresponding to the respective color saturation right value.  

The control takes place when recording z. B. so that in everyone Line the maximum ink carrier amplitude through the modulation range fixed signal peak value of z. B. 0.7 V corresponds. Then, even with a low mean ink carrier amplitude and total color saturation for the color support available amplitude range fully utilized.

Since the recording of color information is no longer with a frequency carriers with reduced frequency below the frequency range of the modulated image carrier can take place so far required band limitation of the lower side band of the image carrier omitted. When recording is a previously required High pass for the image carrier with a cut-off frequency from Z. B. 1.1 MHz is no longer required. This also has the advantage that frequency components below 1 MHz of the modulated image carrier are recorded and thereby the image sharpness in the line direction and the signal-to-noise ratio at the Image reproduction can be increased.

When using transversal filters when recording and when playback it is advantageous to regenerate the lost Perform vertical resolution, otherwise the sharpness in the vertical direction during playback is poor can be. For this purpose, so-called circuits to vertical Aperture correction is known in which signals are consecutive Lines can be combined. Since the signal components for vertical picture details are small, can with the mentioned Regeneration also add noise components. For this Basically, it is advantageous in the recording according to the invention when playing a circuit to increase the vertical details to be used with a frequency boost at 200-500 KHz.

The vertical sharpness reduction is due to used to separate the color carrier and luminance signal Chamber filter conditional in which signals from temporal consecutive lines are added.

The invention is based on the drawing of several embodiments explained. Show in it

Fig. 1 frequency spectra for the inventive recording,

Fig. 2 is a block diagram for the recording,

Fig. 3 is a block diagram for the reproduction at a recording shown in FIG. 2,

Fig. 4 is a block diagram for recording with a different type of sound recording and

FIG. 5 shows a block diagram for the reproduction in a recording according to FIG. 4.

FIG. 1a shows the luminance signal Y with a bandwidth of 3 MHz. In the lower frequency range from 0.13 to 1.13 MHz, the modified color carrier Fm, which is reduced in frequency to 0.63 MHz, is inserted. The frequency of the color carrier is converted from 4.43 MHz to 0.63 MHz in such a way that the quarter-line offset in the color carrier frequency (according to DE-PS 11 79 986) is retained. As a result, the spectral lines of the luminance signal Y and the color carrier Fm are nested. The signal according to FIG. 1a is modulated onto the image carrier in Fm.

Fig. 1b shows the resulting signal. The image carrier B has a frequency of 4.1 MHz for the black value and the horizontally hatched frequency shift of 3.8 MHz for the synchronous base to 4.8 MHz for the white value. The color carrier Fm occupies the frequency range of 2.97-3.97 MHz, shown obliquely hatched. At the frequencies of 1.92 and 2.16 MHz, two sound carriers T 1 m and T 2 m frequency-modulated with sound signals are recorded. These frequency ranges are left out in the frequency range of the image carrier B with appropriate filters. Since the color carrier Fm lies within the frequency range of the image carrier B, the frequency range from 0 to approximately 1.1 MHz is free.

Referring to FIG. 1c, a PCM audio signal is recorded on the principle of so-called biphase PCM in the free frequency range up to about 1.1 MHz. The bandwidth of 1 MHz enables PCM sound recording with high quality.

In Fig. 1d in the free frequency range of 0-1.1 MHz four frequency modulated sound carriers T 1 m ', T 2 m', T 1 m, T 2 m are recorded at the frequencies shown in the free frequency range. The meaning of these four sound carriers is explained with reference to FIG. 2.

Fig. 1e shows the signal obtained during playback by FM femodulation and frequency conversion. This consists of the luminance signal Y with a bandwidth of 3 MHz, the color carrier F converted back to the frequency of 4.43 MHz and the two sound carriers T 1 , T 2 with the standardized frequencies of 5.5 and 5.74 MHz for stereo -Tone transmission or a transmission in two different languages.

FIG. 2 shows a recording circuit for a recording according to FIG. 1d. The tuner 2 , which is fed by the antenna 1 with a television broadcast signal, supplies the standardized FBAS signal and the sound carriers T 1 , T 2 . The CVBS signal is split into the modulated color carrier F and the luminance signal Y using the comb filter 3 . Such comb filters for separating the luminance signal and the color carrier with nested frequency spectra are known and are described in more detail in "Telefunken-Zeitung" 1964, number 2, pages 127-130. The color carrier F passes to the mixing stage 5 via the bandpass 4 tuned to 4.43 MHz + 0.5 MHz. With the synchronous isolating stage 6 , the synchronizing pulses S are separated from the luminance signal Y and fed to the phase comparison stage 7 , which is part of a PLL control circuit with the oscillator 8 and the frequency divider 9 . The oscillator 8 oscillates at a frequency of 5.07031250 MHz = 324.5 fH, where fH is the line frequency. The mixing carrier generated in the oscillator 8 with this frequency is fed to the mixing stage 5 . At the output of the mixer stage 5 , the frequency carrier Fm with the frequency of 0.63669375 MHz, which is reduced in frequency, appears and is supplied to the adder stage 11 via the low-pass filter 10 with a cut-off frequency of 1.15 MHz. The luminance signal Y also passes through the amplifier 12 , the low-pass filter 13 with a cut-off frequency of 3 MHz and the delay element 14 used to compensate for delay time to the adder stage 11 . At the output of the adder 11 there is the signal Fm BAS according to FIG. 1a. This signal passes through the pre-emphasis stage 15 to the FM modulator 16 , which generates the signal according to FIG. 1d without the sound carriers. This signal reaches the adder 18 via the high-pass filter 17 with a cut-off frequency of 1.1 MHz.

The synchronizing pulses S are also fed to the circuit 19 , which is used to generate the mixed carriers for converting the frequencies of the sound carriers T 1 , T 2 , from the tuner 2 via the bandpass filter 20 with a passband of 5.62 MHz ± 200 kHz of the mixing stage 21 are supplied. The circuit 19 contains two PLL circuits, each containing a phase comparison stage, a frequency divider and an oscillator. The frequency dividers each divide the oscillator frequency down to the line frequency fH. The oscillator 22 generates a mixed carrier with the frequency of 4.75 MHz = 304 · fH and the oscillator 23 a mixed carrier with the frequency of 5.25 MHz = 336 · fH. The frequency dividers shown thus have the divider factors 304 and 336, respectively. With the changeover switch 24 , which is switched from field to field by the servo circuit 25 with the 25 Hz switching voltage 26 , the two mixed carriers alternate from field to field Frequencies of the mixer 21 supplied. The mixing stage 21 thus supplies two fields with different frequencies converted from field to field with the following values:

Field 1 :
T 1 m with 5.5-4.75 = 0.75 MHz
and
T 2 m = 5.7421875-4.75 = 0.9921875 MHz.

Field 2 :
T 1 m 'with 5.5-5.25 = 0.25 MHz
and
T 2 m ′ with 5.7421875-5.25 = 0.4921875 MHz.

These sound carriers, which are reduced in frequency and switched from field to field, reach the adder 18 via the low-pass filter 27 with a cut-off frequency of 1.1 MHz. At the output of the adder 18 there is thus the signal according to FIG. 1d, which is fed to the video heads 29 via the amplifier 28 and recorded with them on the magnetic tape 30 .

Fig. 2a shows a modification of the circuit 19. The two oscillators 22 , 23 are replaced by a single oscillator 31 . The frequency generated by the oscillator 31 is switched by switching the divider factor n of the frequency divider by the switching voltage 16 between n = 304 and n = 336.

The described switching of the frequencies of the sound carriers T 1 , T 2 has the following purpose. At the frequency position of the sound carriers indicated in FIG. 1d, the so-called azimuth losses, which cause crosstalk attenuation between adjacent inclined tracks, are no longer effective. Crosstalk between adjacent tracks would therefore occur for the recorded sound carriers. If the frequency of the sound carrier is switched from field to field, the sound carriers in two adjacent inclined tracks have different frequencies, which can be separated from one another during playback with filters. Crosstalk between the sound carriers of adjacent inclined tracks is thus avoided. This solution is described in more detail in the subsequently published DE-OS 33 06 978.

In Fig. 2, the oscillator 8 oscillates above the frequency of the color carrier F. If the oscillator 8 is to oscillate below the frequency of the color carrier F, a mixed frequency of 3.79687500 MHz = 243 * fH is preferably selected when recording, so that for the color carrier Fm results in a frequency of 0.63674375 MHz. During playback, this mixed carrier with the same frequency again increases the frequency to 4.4361875 MHz. The recording of the sound carrier T takes place with approximately 10-20% of the recording current of the image carrier B in order to avoid disturbing interference during playback.

In FIG. 3, the signal according to FIG. 1d is scanned from field to field by the inclined tracks of magnetic tape 30 with switch 32 operated by switching voltage 26 and video heads 29 . This signal passes through the limiter 33 to the FM demodulator 34 , which generates the signal according to FIG. 1a. This signal passes through the low-pass filter 35 with a cut-off frequency of 3 MHz and the de-emphasis stage 36 and the amplifier 37 to the inputs of the two comb filters 38, 39 . The comb filters 38, 39 are designed such that they separate the nested frequency spectra of the luminance signal Y and the color carrier F. The comb filter 38 supplies the luminance signal Y to the adder stage 41 via the delay element 40 , which serves to compensate for the delay. The comb filter 39 supplies the color carrier Fm of 0.63 MHz, which is fed to the mixer 43 via the low-pass filter 42 with a cut-off frequency of 1.1 MHz. The synchronizing pulses S are also derived from the amplifier 37 with the synchronizing pulse isolating stage 44 and supplied for the synchronization of the PLL circuit 45 with the oscillator 46 , which operates in accordance with the circuit 19 in FIG. 2. The oscillator 26 generates a mixed carrier with the frequency of 5.07 MHz = 324.5 · fH. The mixing stage 43 thereby again delivers the color carrier F at the output with the PAL color carrier frequency of 4.43361875 MHz, which reaches the adder stage 41 via the bandpass 47 with a pass band of 4.43 ± 0.5 MHz. The FBAS signal corresponding to the standard is thus available at terminal 48 .

The synchronizing signal S also synchronizes the PLL circuit 49 . Its oscillator 50 alternately generates two mixing carriers with frequencies of 4.75 and 5.25 MHz from field to field, which reach mixer stage 51 . For this purpose, the divider factor n of the frequency divider of the PLL circuit 49 is switched by the 25 Hz switching voltage 26 from field to field between the values n = 304 and n = 336. At the output of the mixer 51 , the two sound carriers T 1 , T 2 with the standardized frequencies of 5.5 and 5.7421875 MHz are then produced, which are the amplifiers via the bandpass 52 with a pass band of 5.62 ± 0.2 MHz 53 , the limiter 54 and the amplifier 55 of the output terminal 56 are supplied. The signals at terminals 48, 56 thus again form the complete television signal with picture and sound information.

A pulse 58 which occurs during the head change is generated from the switching voltage 26 with the pulse shaper 57 and briefly increases the gain of the amplifier 53 . This can reduce head interference. The pulse 58 can act in the sense that it causes the amplifier 23 to oscillate naturally at its resonance frequency during the head change, so that even if the sound carriers T 1 , T 2 fail at the output of the bandpass 52 , sound carriers are still produced. This solution is described in more detail in DE-OS 31 16 130.

FIG. 4 shows a recording circuit for the type of recording according to FIG. 1b. The color carrier F is converted to a color carrier Fm with the reduced frequency of 0.63 MHz using the mixing stage 59 and the oscillator 60 , as in FIG. 2, and is added to the luminance signal Y in the adder stage 61 . The combined signal passes to the FM modulator 62 and from there to the filter 63 , which has blocking points at the frequencies 1.92 and 2.16 MHz. The sound carriers T 1 with 5.5 MHz and T 2 with 5.7421875 MHz are converted by the mixer 64 and the oscillator 65 to sound carriers T 1 m with 1.92 and T 2 m with 2.16 MHz. These sound carriers are added in the adder 66 to the signal coming from the filter 63 . The output signal of the adder 66 in Fig. 1b is recorded with the video head 29 on the magnetic belt 30. In this exemplary embodiment, the sound carriers lie within the frequency range of the image carrier B, while the frequency range below from about 0 to 1.1 MHz remains free for other signals.

Fig. 5 shows the corresponding playback circuit. The signal scanned with the video heads 29 from the magnetic tape 30 according to FIG. 1b reaches the filter 63 , which corresponds to the filter 63 in FIG. 4. With the filter 63 , the sound carriers T 1 m and T 2 m are suppressed. The FM demodulator 67 delivers the signal according to FIG. 1a. This is split up with the comb filters 68, 69 into the luminance signal Y and the color carrier Fm. The color carrier Fm is converted back to the original frequency of 4.43 MHz with the oscillator 70 and the mixing stage 71 and fed to the adder stage 72 . This supplies the standardized FBAS signal again at terminal 73 .

The two sound carriers T 1 m and T 2 m are selectively evaluated with the bandpasses 74.75 tuned to 1.92 and 2.1 MHz and fed to the adder 76 . The frequencies of these two sound carriers are converted to the original frequencies of 5.5 and 5.742 MHz with the oscillator 77 and the mixer 78 as in FIG. 3, so that the standardized sound carriers T 1 , T 2 are again at the terminal 79 . The signals at the terminals 73, 79 thus again form the standardized television broadcast signal for the picture information and the sound information. Switching the sound carrier frequencies acc. FIG. 2 is not necessary here because the azimuth loss to crosstalk attenuation are sufficiently effective in the frequency range of 2 MHz.

The oscillator 8 in FIG. 2 and the oscillator 46 in FIG. 3 oscillate at the same frequency and are coupled to the line frequency in the same way, because the frequency reduction of the color carrier when recording and the conversion during reproduction take place at the same mixed carrier frequency. For this reason, the same steps can be used for the recording and for the reproduction, that is to say the steps 5 , 7 , 8 , 9 in FIG. 2 can fulfill the function of the steps 43, 35 , 46 in FIG . The same applies to the corresponding conversion of the frequencies of the sound carriers T 1 , T 2 , because the frequency conversion of the color carrier and the sound carrier take place in the same way.

Claims (16)

1. Video recorder with recording of a PAL color carrier (F) and an image carrier (B) frequency-modulated with the luminance signal, characterized by the following features:

• a) The frequency of the color carrier (F) is converted to a frequency (0.63 MHz) in the lower frequency range of the luminance signal (Y) while maintaining the PAL quarter offset and added to the luminance signal (Y) ( Fig. 1a).
• b) The combination of the luminance signal (Y) and the color carrier (Fm) is modulated onto the image carrier (B) in FM and recorded in this form.

2. Recorder according to claim 1, characterized in that during playback the frequency of the color carrier (Fm) is converted back to the value corresponding to the norm ( Fig. 3, 5). 3. Recorder according to claim 1 or 2, characterized in that the implementation of the frequency of the color carrier (Fm) with a mixed carrier, whose frequency is in full line offset or in half-line offset with the line frequency is coupled. 4. Recorder according to claims 1-3, characterized in that the mixing carrier is derived during recording and playback from the same, coupled to the line frequency oscillator ( 8, 46 ). 5. Recorder according to claim 1, characterized in that during recording and / or during playback the luminance signal (Y) and the color carrier (Fm) with comb filter ( 3, 38, 39, 68, 69 ) are separated from each other ( Fig. 2, 3, 5). 6. Recorder according to claim 1, characterized in that below the frequency range occupied by the image carrier (B) a sound signal is recorded. 7. Recorder according to claim 6, characterized in that the Sound signal is recorded by FM of a sound carrier (T). 8. Recorder according to claim 7, characterized in that the Frequency of the sound carrier (T) from field to field between two different values is switched. 9. Recorder according to claim 1, characterized in that the sound signal is a PCM signal. ( Fig. 1c). 10. Recorder according to claim 7, characterized in that at recording the frequency of the sound carrier (T) with a Mixed carrier implemented at a lower value and at playback with the same mixing medium back to that of The value corresponding to the norm is converted back. 11. Recorder according to claim 10, characterized in that at the reduction in the frequency of the sound carrier (T) which in the existing full line offset or half line offset is maintained by the frequency of the mixed carrier is coupled to the line frequency (fH). 12. Recorder according to claim 7, characterized in that the Amplitude of the sound carrier (T) about 10-20% of the amplitude of the Image carrier (B) is. 13. Recorder according to claim 1, characterized in that at the recording and / or during playback in the way of the luminance signal (Y) a circuit for increasing the sharpness of the image lies in the horizontal direction.   14. Recorder according to claim 1, characterized in that at playback a circuit to increase the sharpness of the image is provided in the vertical direction. 15. Recorder according to claim 1, characterized in that at the recording the amplitude of the frequency reduced Color carrier (Fm) including color synchronizing signal before adding to the luminance signal (Y) in each Line on an independent of the medium color saturation, approximately constant maximum value is controlled. 16. Recorder according to claim 15, characterized in that at playback by comparing the amplitude of the color burst signal and the sync pulse a control voltage won and thus the amplitude of the color carrier in each line (Fm) back to that of the respective color saturation corresponding value is controlled.