JPH0210504A - Magnetic recording method for angle modulating signal - Google Patents

Abstract

PURPOSE:To reduce the generation of unnecessary elements for moire generating factors caused by mixing the lower side wave component of the third higher harmonic wave of a frequency modulating signal into a used band by angle- modulating a special carrier with an input signal, and recording it on a magnetic recording medium. CONSTITUTION:When one cycle is set at T, a signal, whose level in zero to T/6 period is at zero, whose level in T/6 to T/2 period is at A, whose level in T/2 to (2/3)T period is at zero, and whose level in (2/3)T to T period is at -A, is made into the carrier, the carrier is angle-modulated by the input signal, and recorded on the recording medium. That is, at the time of recording, a video signal inputted from a terminal 1 is supplied to a frequency modulator 2, its frequencies are modulated, and its output signal is supplied to a 1/6 dividing circuit 3. The 1/6 dividing circuit divides the frequency modulating signal to the 1/6 frequencies, and two square signals whose phase are mutually different at 60 deg. are outputted. These two output signals are supplied to an adder 4, and added at the amplitude ratio of 1:1. Thus, the moire components can be reduced.

Description

Detailed Description of the Invention Field of the Invention The present invention relates to a recording method for recording angle modulated signals on a magnetic recording medium, and in particular to a video tape recorder and a magnetic disk that frequency modulate and record video signals. This document relates to a recording method suitable for such devices.

Conventional technology: In video tape recorders and other devices that record and play back video signals by frequency modulating them, unnecessary components are mixed into the playback signal.
A moiré phenomenon may occur on the screen. The main reasons for this are (1) when lower sideband waves are folded back at zero frequency in the recorded frequency modulated signal and mixed into the used band as unnecessary spurious signals; (2) when the frequency modulator is With a square wave oscillator such as a vibrator, if the lower sideband from the third harmonic of the carrier wave mixes into the used band, ((9
) If unnecessary components are generated due to non-linear distortion in the electromagnetic conversion system and mixed into the used band, (4) The FM demodulator is a pulse count type doubler demodulator, and the frequency modulation signal has a double wave. It is known that lower sideband waves mix into the demodulation band.

Since the present invention relates to 2 and 3 of these main causes of moiré, these will be explained in more detail. First, the occurrence of unnecessary spurious when the carrier wave is a square wave will be explained. When the carrier wave is a square wave, the amplitude of the third harmonic component is one-third that of the fundamental wave component, but
The harmonic components are also frequency modulated, and the modulation index is three times the modulation index of the fundamental wave, so the amplitude of the sideband is relatively large. - As an example, if the carrier frequency fC is 6, sMHz
Modulating signal frequency f. 3, OMHz, modulation index 0.
7 shows the main frequency spectrum in FIG.

When recording a video signal of 0 to 4.5 MHz, as shown in Figure 5, the unnecessary components that mix into the used band are the 3fC-3frn component, which is the lower sideband of the third harmonic, and the 3fo-
4fm component and the fC-3fm component in which the lower sideband wave of the fundamental wave is folded back at zero frequency.

Further, the lower sideband component of the third harmonic has a larger vibration than the folded component.

Next, distortion and unnecessary spurious generated in the electromagnetic conversion system will be explained. The relationship between the recording signal waveform and the residual magnetization waveform is basically an S-shaped one, as described in documents such as "Magnetic Recording Technology Tube 3, P177, Japan Industrial Technology Center, published June 3, 1982." Since it is thought that the initial magnetization curve will be similar to the initial magnetization curve, the residual magnetization waveforms when saturated recording of a sine wave and a square wave are almost equal, as shown in Figures 6 and 7, and both have square wave-like residuals. It becomes a magnetization waveform.

Therefore, in a video tape recorder that performs saturation recording, even if the carrier wave of the frequency modulated signal is a sine wave, the lower side band of the third harmonic is within the used band, which is almost equivalent to recording a frequency modulated signal whose carrier wave is a square wave. It will be recorded and played back again.

Problems to be Solved by the Invention As mentioned above, since FM signals are recorded in saturation, even if the carrier wave is a sine wave, it is the same as recording a square wave, and moiré from the third harmonic is used. mixed into the band.

The present invention deals with the cause of moiré caused by the lower side wave component of the third harmonic of the frequency modulation signal generated in the frequency modulator and electromagnetic conversion system mixed into the usage band. The aim is to reduce the occurrence of

Means for Solving the Problem A signal whose level is o during the period and -A during the T-T period is used as a carrier wave, and this carrier wave is angularly modulated by an input signal and recorded on a magnetic recording medium. .

Function Therefore, the carrier waveform of the frequency modulated signal recorded in the present invention is shown in FIG. 1) Equation becomes.

A is the amplitude and ω is the angular frequency.

In other words, the third harmonic component, which is a problem in the conventional method, is not included, and therefore, the frequency modulated signal using this as a carrier wave does not include the third harmonic and its sideband components.

Furthermore, when this carrier wave is recorded, the shape of the residual magnetization waveform does not change even if saturated recording is performed, as shown in Figure 2, assuming that there is no recording demagnetization loss or self-demagnetization loss, and therefore the shape does not change due to electromagnetic conversion. In the system as well, sideband waves of the third harmonic of the carrier wave are difficult to mix into the used band.

Embodiments Hereinafter, embodiments in which the present invention is implemented in a video tape recorder will be described. FIG. 3 is a block diagram of the video signal processing section, and FIG. 4 is a signal waveform diagram. When recording,
A video signal input from a terminal 1 is supplied to a frequency modulator 2 where it is frequency modulated, and its output signal A is supplied to a 1/6 frequency divider circuit 3. In the 1/6 frequency divider circuit, the frequency modulation signal is divided into 1/6 frequency and the signal port and the co
Two square signals having different degrees and phases are output. These two output signals are supplied to an adder 4 and added in an amplitude ratio of 1:1. Therefore, as shown in signal 2, the output signal of the adder 4 is as follows: t when the level of the carrier wave during non-modulation is A, -~-d period, o, and t when the level of the period is o, and -T-T period.
When the level of the period is -8, the frequency modulated signal becomes a frequency modulated signal that does not include the third high frequency and its sideband waves, as described above. The output signal of the adder 4 is supplied to a recording amplifier 5, amplified, and recorded in saturation on a magnetic tape 7 via a recording magnetic head 6.

During reproduction, a frequency modulated signal is reproduced from the magnetic tape 7 by the reproduction magnetic head 8, and is supplied to the reproduction amplifier 9 and amplified. The output signal of the regenerative amplifier 9 is the regenerative equivalent h10
The frequency versus amplitude characteristics due to electromagnetic conversion during playback are corrected. The output signal of the reproducing isolateral type 1o is supplied to a frequency converter 11, where it is converted to a higher frequency. The output signal of the frequency converter is supplied to a limiter 12, amplitude fluctuations are removed, and the output signal is supplied to an FM demodulator 13 for demodulation.

Therefore, the reproduced video signal is output to the terminal 14.

Therefore, when the configuration shown in FIG. 3 is used, the output signal of the adder 4 does not include the third harmonic of the carrier wave and its harmonic wave, and the electromagnetic conversion system shown in FIG. As explained above, since the waveform of the recording signal is maintained and magnetized on the tape, third harmonics and their sidebands are less likely to occur. Therefore, the third harmonic and its sideband components are also small in the frequency modulated signal reproduced by the magnetic head 8, and by demodulating the frequency modulated signal with fewer unnecessary components, a video signal with less unnecessary components mixed in can be obtained. can be played.

Effects of the Invention Since the present invention can reduce moire components, when applied to a video tape recorder, high quality images with less unnecessary components can be reproduced. Furthermore, since the moiré component increases as the modulation index increases, the method of the present invention allows the modulation index to be increased compared to the conventional method.
/N ratio can be improved.

[Brief explanation of the drawing]

Fig. 1 is a carrier wave waveform diagram of an angle modulation signal used in the magnetic recording method of the present invention, Fig. 2 is a relationship diagram between the recording signal waveform and residual magnetization waveform in the magnetic recording method, and Fig. 3 is a diagram showing the relationship between the recording signal waveform and the residual magnetization waveform in the magnetic recording method. A block diagram showing the video signal processing of the video tape recorder that has been applied, FIG. 4 is a waveform diagram of each part in FIG. 3,
Figure 6 is a spectrum of a frequency modulated signal whose carrier wave is a square wave. Figure 6 is an illustration of residual magnetization when the recording signal is a sine wave. Figure 7 is an illustration of residual magnetization when the recording signal is a square wave. It is a diagram. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 11 Lost (MHXI)

Claims (1)

[Claims] When one period is T, the level from O to T/6 period is O,
Level of T/6 to T/2 period is A, T/2 to (2/3)
The carrier wave is a signal whose level is O during the T period and -A during the (2/3)T to T period, and this carrier wave is angularly modulated by an input signal and recorded on a magnetic recording medium. Magnetic recording method for angle modulated signals.