JPH05325112A - Video tape recorder - Google Patents

Abstract

PURPOSE:To prevent a cross modulation distortion component from coming within a color signal band by setting the frequency of erase signal at a predetermined high level. CONSTITUTION:Standard or high picture quality mode recording is carried out by means of a rotary recording and reproducing heads 21, 22 in a plurality of recording modes where FM image signals have different carrier frequencies. Previously recorded image information is erased by means of an erase head 23 prior to the recording operation. When the frequency of the erasure signal is set at about 10 MHz which is sufficiently higher than the carrier frequency, cross modulation distortion components do not come within a color signal bandwidth and thereby cross modulation distortion is eliminated from each recording mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video tape recorder (hereinafter referred to as VT) having a rotary erasing head for erasing a video signal.
R), and particularly to prevent cross modulation distortion at the time of recording due to the erasing frequency.

[0002]

2. Description of the Related Art In a conventional home-use VTR, when a new video signal is overwritten or insert-recorded on a magnetic tape having a video signal recorded, the video signal is erased in the tape width direction by a full-width fixed erasing head. After that, a method of recording a new video signal with the recording / reproducing rotary head is adopted, but since the recording / reproducing rotary head is arranged at a stage subsequent to the fixed-width fixed erasing head, overwrite or insert recording is performed. For a few seconds after the start, an area which is not erased by the fixed-width erase head occurs on the magnetic tape. Therefore, when a new video signal is recorded in this area, the video signal (especially the color signal) recorded over the deep layer of the magnetic tape.
Was not completely rewritten, and there was a problem that rainbow-shaped noise (hereinafter referred to as rainbow noise) was generated on the screen during playback.

In order to solve this problem and realize overwriting and insert recording in which rainbow noise does not occur, a circuit as shown in FIG. 3 has been proposed. (See JP-A-59-146407) In FIG.
22 is a rotary head for recording and reproducing video signals,
These are mounted on a rotating cylinder at an angle of 180 °. Reference numeral 23 is a rotary erasing head, which usually has a gap length several times as large as that of the recording / reproducing rotary head, and is supplied with an erasing current of, for example, 8.5 MHz to erase the video signal recorded on the magnetic tape. It should be noted that although there is only one erasing head 23 in this case, this sets the track width of the rotary erasing head to about twice that of the rotary heads 21 and 22 for recording and reproducing, and makes two scans of video tracks in one scan. Is supposed to be erased. In order to erase one track at a time, the track width of the erase head may be the same as the recording track width and two tracks may be provided.

It is well known that the rotary heads 21, 22 and 23 are connected to the fixed side circuit by the rotary transformer 24, and the rotary heads 21 and 22 for recording and reproduction are the channels 25 of the rotary transformer 24. The recording / reproducing changeover switch 2 is connected to the recording amplifier 35 via 26.
8, 29, 30 and 31 and further connected to regenerative amplifiers 32 and 33.

At the time of reproduction, the recording / reproduction changeover switches 28 to 31 are brought into the connection state shown in the drawing, and the rotary head 21,
The output of 22 is the channels 25 and 26 of the rotary transformer 24.
After being amplified by the reproduction amplifiers 32 and 33 via the head, the head switching circuit 34 selects and outputs a period during which each head is in contact with the magnetic tape. At the time of recording, the recording / reproducing changeover switches 28 and 30 are opened, 29 and 31 are closed, and the recording signal is obtained by the recording amplifier 35 and the rotary transformer 24.
Channels 25, 26 of the rotary head 21,
A recording current will be applied to the recording medium 22. Rotation erasing head 23
An erasing current obtained by amplifying the output of the erasing oscillator 37 by the erasing signal amplifier 36 is supplied to a channel 27 of the rotary transformer 24. As a result, when a new video signal is recorded on the magnetic tape, an erasing current is supplied to the rotary erasing head 23 at the same time as the recording, so that the disturbance of the image does not occur at the joint between the recording and the rainbow noise does not occur. Therefore, it is suitable for tape editing such as overwriting and insert recording.

[0006]

In the above prior art, the erasing frequency output from the erasing oscillator 37 is supplied to the rotary erasing head 23 through the erasing signal amplifier 36, and the erasing frequency is used for the recording / reproducing rotation. Heads 21 and 22
However, if the video signal is recorded on the magnetic tape in this state, there is a problem that intermodulation distortion occurs with the carrier frequency of the frequency modulation luminance signal. FIG. 2a shows a frequency spectrum of the current VTR standard mode (hereinafter, this mode is referred to as a standard mode). Explaining the frequency spectrum here, first, Fys, Fyp,
Fyw indicates the carrier frequency at the sync tip level, pedestal level, and white level of the luminance signal, respectively, and in the standard mode, Fys is 3.4 MHz, Fyp.
Is 3.8 MHz, Fyw is 4.4 MHz, and frequency deviation is 1 MHz. That is, the intermodulation distortion component generated between the erase frequency Fr and the carrier frequency of the frequency-modulated luminance signal, for example, Fyp, is expressed by the following formula.

[0007]

[Equation 1]

[0008]

In the standard mode, the color signal band is 629K.
Hz ± 500 KHz, and when the erasing frequency Fr is set to 8.5 MHz as described above, (Fr
The difference frequency component of −2 Fyp) enters the color signal band, and intermodulation distortion occurs during recording.

Further, in recent home VTRs, due to improvements in the performance of magnetic tapes and the performance of magnetic heads, the carrier frequency of the frequency-modulated luminance signal is set higher than that of the current VTR standard for recording and reproduction. Therefore, a recording / reproducing method in a high image quality mode is adopted in which an image having a high resolution and a higher image quality than an image recorded and reproduced in the standard mode is obtained. For example, the frequency spectrum in the high image quality mode has Fys of 5.4 MHz and F
yp is 5.8 MHz, Fyw is 7.0 MHz, and frequency deviation is 1.6 MHz. Therefore, even in the high image quality mode, if the erasing frequency Fr is not properly set, intermodulation distortion may occur during recording.

Therefore, it is an object of the present invention to provide a video tape recorder having an erasing frequency which does not cause cross modulation distortion in both the standard mode and the high image quality recording mode.

[0012]

In order to solve the above problems, a video tape recorder of the present invention records on a magnetic tape in one of a plurality of recording modes in which carrier frequencies of frequency-modulated video signals are different from each other. A rotary head for recording / reproducing and a rotary erasing head for erasing the video signal recorded on the magnetic tape prior to the rotary head for recording / reproducing are provided, and the erasing frequency of the rotary erasing head is a carrier of the plurality of recording modes. The configuration is set sufficiently higher than the frequency and the erasing frequency is set so that the intermodulation distortion component does not enter the color signal band.

[0013]

According to the present invention, the erasing frequency of the rotary erasing head is set sufficiently higher than the carrier frequencies of both the standard and high image quality modes, and the erasing frequency is set so that the intermodulation distortion component does not enter the color signal band. By setting, high quality overwriting and insert recording without moire can be performed.

[0014]

Embodiments of the present invention will be described below with reference to FIG. 1 and Tables 1 and 2.

FIG. 1 shows a recording system of a video tape recorder. The same circuits as those in FIG. 4 are designated by the same reference numerals, and the description thereof is omitted. First, the video signal input to the input terminal 1 is a low pass filter (LPF) 2 and 3 and a band pass filter (BP).
F) 4 is supplied to each. The BPF 4 filters a carrier color signal from the incoming video signal and outputs it to the color signal recording processing circuit 5. The color signal recording processing circuit 5 frequency-converts the carrier color signal into a low-frequency converted carrier color signal and supplies it to the adder 6.

On the other hand, LPF 2, comb filter 7, pre-emphasis circuit 8 and FM modulator 9 are for standard mode, L
PF3, comb filter 10, pre-emphasis circuit 1
1. The FM modulator 12 constitutes a luminance signal recording processing circuit for the high image quality mode.

Here, both luminance signals filtered from the video signal from the input terminal 1 by the LPFs 2 and 3 and the comb filters 7 and 10 are given the pre-emphasis characteristic and are FM-modulated, and then the switching circuit. It is outputted to the terminals 13a and 13b of 13.

A mode switching signal corresponding to a recording mode set by a mode selection switch or the like (not shown) is supplied to the switch circuit 13 via a terminal 14.

Therefore, when the recording mode is the standard mode, the switch circuit 13 is switched to the terminal 13a side, while when the recording mode is the high image quality mode, the switch circuit 13 is switched to the terminal 13b side.

As described above, the frequency-modulated luminance signal FM-modulated with the carrier frequency according to the recording mode and having the pre-emphasis characteristic according to the recording mode is output from the switch circuit 13 to the adder 6. .

The adder 6 adds the frequency-modulated luminance signal and the low-frequency converted carrier color signal and supplies them to the rotary heads 21 and 22 via the recording amplifier 35 and the rotary transformer 24 to record them on the magnetic tape. Then, the erase oscillator 37 is operated at the same time as the recording system to supply an erase current to the rotary erase head 23 through the erase signal amplifier 36.

By the way, the band of the frequency-converted chrominance signal is set to 629 KHz ± 500 KHz. A frequency difference component from Fr may enter and intermodulation distortion may occur during recording.

Therefore, in the present invention, since the erasing frequency Fr is set to a value that does not cause cross modulation distortion in both the standard and high image quality recording modes, cross modulation distortion components are set as shown in Tables 1 and 2. It was calculated by the equation 1.

[0024]

[Table 1]

The frequency deviations Fy in the standard and high image quality modes are 3.4 to 4.4 MHz in the standard mode.
Although it is 5.4 to 7.0 MHz in high image quality mode,
The signal band actually recorded as a video signal is about 3.7 to 4.4 MHz in the standard mode and 5.8 to 5.8 in the high image quality mode.
Since it is 7.0 MHz, this band is set as a vertical parameter at 50 KHz intervals, and the erase frequency Fr is set.
Was set as a horizontal parameter at 500 KHz intervals.

From Table 1, in the standard mode, by setting the erasing frequency to about 10 MHz or more, the intermodulation distortion component does not occur in the color signal band. On the other hand, in the high image quality mode, it was found that the intermodulation distortion component did not occur in the color signal band by setting the erasing frequency to less than 11 MHz.

In order to obtain more detailed data, the intermodulation distortion component when the erasing frequency Fr was changed from 9.8 MHz to 10.6 MHZ at 100 KHz intervals was obtained in Table 2.

[0028]

[Table 2]

From this result, ± 200 KHz around 10.2 MHz (however, since the color signal components actually recorded are distributed around 629 KHz, ± 400 KHz
If the erasing frequency Fr is set within the range of (increasing to Hz), the intermodulation distortion that occurs in the color signal band does not occur in both the standard and high image quality recording modes. Therefore, high-quality overwriting and insert recording can be performed without causing moire beat noise.

[0030]

As described above, according to the present invention, in both the standard recording mode and the high image quality mode, the erasing frequency which does not cause the intermodulation distortion is calculated and the optimum value is set, thereby simplifying the circuit configuration. In addition, it is possible to perform high-quality overwriting and insert recording without causing moire.

[Brief description of drawings]

FIG. 1 is a block diagram showing a video tape recorder which is an embodiment of the present invention.

FIG. 2 is a diagram showing frequency spectra in a standard mode and a high image quality mode.

FIG. 3 is a diagram showing a rotation erasing unit of a conventional video tape recorder.

[Explanation of symbols]

 5 color signal recording / reproducing processing circuit 8 pre-emphasis circuit 9 FM modulator 11 pre-emphasis circuit 12 FM modulator 21 recording / reproducing rotary head 22 recording / reproducing rotary head 23 rotary erasing head 24 rotary transformer 37 erasing oscillator

Claims (2)

[Claims] 1. A recording / reproducing rotary head for recording on a magnetic tape in one recording mode among a plurality of recording modes in which the carrier frequencies of frequency-modulated video signals are different from each other, and the magnetic tape prior to the recording / reproducing rotary head. In a video tape recorder equipped with a rotation erasing head for erasing the video signal recorded in, the erasing frequency of the rotation erasing head is set sufficiently higher than the carrier frequency of the plurality of recording modes, and the intermodulation distortion component is colored. A video tape recorder characterized in that the erasing frequency is set so as not to enter the signal band. 2. The erasing frequency of the rotary erasing head is approximately 1
The video tape recorder according to claim 1, wherein the video tape recorder is set to 0 MHz.