JPS586436B2 - Jikiki Roku Saisei Hoshiki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recording and reproducing color television signals. The purpose is to insert and record a pilot signal for removing the shifter during reproduction so as not to particularly affect the carrier color signal.

The mainstream of current home VTRs is the low frequency conversion recording and reproducing method as shown in FIG. 1A.

To briefly explain this system (the NTSC system will be explained below as an example), the input color television signal is 1
The /2 offset signal has an interleaving relationship between the sudden signal and the luminance signal.

This color television signal is divided into a luminance signal and a color signal (subcarrier signal frequency is 3.5 8 MHZ = ft2
), and the luminance signal is angularly modulated on the Takagi side (
For convenience of explanation, it is assumed to be FM modulation), and the frequency of the sudden signal is converted to the lower frequency side.

Let fB be the low frequency converted giant signal frequency.

In general, fB is considered to have a frequency between 500 KHz and 800 KHz.

The angle modulated wave and the low frequency converted color signal f8 are superimposed and recorded on a magnetic medium by a video head.

In this low frequency conversion recording and reproducing method shown in Figure 1A, to correct jitter in the sudden signal, a continuous signal that is phase-synchronized with the reproduced burst signal is created using an APC circuit, the jitter is canceled out by this continuous wave, and the video output and A method is being taken to do so.

Another method is a low frequency conversion pilot recording/reproducing method as shown in FIG. 1B and C.

B is a signal obtained by angle modulating the luminance signal and a sudden signal at approximately IMH
This is a method of recording and reproducing by superimposing a pilot signal (continuous wave) on a low-frequency converted signal near z and a pilot signal (continuous wave) at about 1/3 of the low-frequency converted signal frequency f8 (here, about I MHz).
Convert pilot signal to low band Out of band of sudden signal (fS ±5
50KHz), the transmission band for recording and reproduction is wider than that in A.

C is a low-conversion pilot method when using the same transmission band as B. In order to send the pilot out of the band of the low-conversion signal, the low-conversion color signal band (fS ±5
00KHz) width or the luminance signal bandwidth.
For example, within (±550 KHz), for example, (±350 KHz) is shown.

Comparing the advantages and disadvantages of A, B, and C, we find that APC uses an APC circuit for jitter correction, which makes the circuit more complicated and poses a problem with the follow-up characteristics of the circuit.

B, C: To use the pilot for jitter correction,
Although the tracking characteristics of the circuit are good, the influence of the pilot signal is generally more likely to appear on the screen, and there are problems with the recording band.

The present invention uses the above-mentioned low-pass conversion pilot method, which has a narrow band (Fig. 1A) and does not use APC, so the circuit has good followability.
There is less horizontal scratching noise and tailing (residual errors) on the screen.
Moreover, it provides a recording and reproducing method that is not affected by pilot signals.

The present invention will be described in detail below with reference to the drawings.Generally, the low frequency conversion color signal frequency f8 is determined as follows.

Equation (1) means a 1/4 offset signal.

This is because distortion at twice the frequency tends to occur in magnetic recording and reproducing devices.If the angle modulation frequency is f1, then in an angle-modulated RF system, f1 ±2fs, and when demodulated, the 2f8 component appears as a beat on the screen. It appears.

It has been found through experiments that if this beat is set as a ±45° or 1/2 offset signal on the screen, this beat will not cause any visual problem.

To avoid this, many devices use a 1/4 offset signal for fS.

In Japan, m = 97 in equation (1), fs = 7 6 7.
0 4 5KHz, m-8 7, fs = 6 8
8.3 7 4KHz is the most common.

(Hereinafter, in the present invention, f8=7 6 7. 0 4 5KH
The case of z will be explained.

The recorded spectrum of the present invention is shown in FIG. 1-2.

As can be seen from the drawing, in order to enable narrowband transmission, a pilot signal f is inserted within the band of the low-frequency conversion color signal f8.
P is superimposed and transmitted.

Next, the method for determining fP will be described.

(1) f is 1/r of fS to simplify signal processing.
(2) Let fS and fP have an interleaving relationship. Simplifying equation (6), in equation (7), 2m+1=odd number and 2k+1=odd number, so 2(2k+1)=even number, so The right side will be an odd number.

When finding n that satisfies equation (7), m=97, so n=3.

Therefore, fP is also an offset signal, 2
Double harmonics can also be visually reduced.

Now, fP and fS selected in this manner and the angle modulated wave are recorded on the magnetic medium with a spectrum as shown in FIG. 1, 2.

A basic block diagram of the invention is shown in FIG.

Reference numeral 1 denotes an input color television signal, which is connected to a low-pass filter 2 and a band filter 6, and is separated into a luminance signal and a color signal.

This separated luminance signal is angularly modulated by an angle modulator 3, a certain individual band is suppressed by a Takagi filter 4, amplified by a recording amplifier 5, and mixed with a low-intensity converted color signal, which will be described later, by a mixer 10. The recorded data passes through a recording/reproducing switch 11 and is recorded on a magnetic medium by a video head 12.

On the other hand, the frequency of the separated signal ``ho'' is converted into a continuous signal (to be described later) by a frequency converter 7 to create ``he+ho'' and ``he-ho'' signals, and a low-pass filter 8 extracts ``he-ho''.

Heho=f8, which is the low-frequency converted color signal f.

This f8 is connected to the pilot mixer 9, and the pilot signal oscillator 13 creates a continuous wave with a frequency of fs/n, and the pilot mixer 9 adds the low-pass conversion color signal fS and the continuous wave fs/n, and mixes connected to the device 10.

The output C of 10 becomes the spectrum shown in FIG. 1, 2.

The output of the pilot signal oscillator 13 is connected to the recording/playback switch 22, and in the recording mode, the output of the pilot signal oscillator 13 passes through the switch 22 and is connected to the n-multiplying circuit 23.
is multiplied by x n = f frequency f8
The third frequency converter 25 converts this continuous wave of frequency f8 into a stable crystal oscillator 24 (oscillation frequency f.

13. 5 8 MHz) and f.

A continuous wave of the sum and difference of +f8 and fo-f8 is created, and the bandpass filter 26 filters f.

Create a continuous wave of +f8. This continuous wave of fC+f8 is as described above.

The output of this band filter 26 is connected to the first frequency converter 7 described above and the second frequency converter 17, which will be described from now on. A signal obtained by superimposing a pilot signal on the area-converted signal is input, and 17 outputs and differences are created.
By means of the bandpass filter 18, the difference side, i.e., the chrominance signal and the pilot signal at frequency fc are eliminated forever).

As shown in FIG. 4, this signal is a color signal (8.58 MHz) with a frequency fC, and the spectrum is a color signal with a frequency fC, as shown in FIG.

The amount of energy decreases as the maximum value becomes f±f, f+2f, and so on.

Since the portion shown in FIG. 4 lies in the energy of the color signal component in FIG. 2, it can be separated using a comb filter, which is a conventional technique.

In other words, 19 is a comb filter for rapid signal extraction, and if you take the sum (depending on the system, it may be the difference) of the undelayed signal and the signal delayed by one horizontal scanning period, the signal S/N is approximately 3d.
In the luminance signal processing, the output of the Takagi filter 4 passes through the Takagi filter 14, and the amplitude fluctuation due to the touch of the head tape ( In the recording system, this fluctuation does not occur) is removed by a limiter circuit 15, demodulated by an angle demodulator 16 to form a video signal, and a mixer 27 adds the processed sudden signal to the demodulated luminance signal. This results in a video output 28.

Here, the parts necessary to record on the magnetic medium are 1, 2, 3
,4,5,6,7,8,9,10,IL12,13,2
2, 23, 24, 25.26, and in order to monitor the signal, 14, 15, 16. 17. 18, 19
, 27.28 are required.

Next, the behavior during playback will be explained.

The signal from the tape is converted into an electric signal (FIG. 1) by the video head 12, the recording/reproduction switch 11 is turned to the reproduction side d (dc during recording), and the signal is connected to the Takagi filter 14 and the low-pass filter 8. , the superimposed L and fv signals of the angle-modulated luminance signal, the color signal of frequency f8, and the 79 lot signal of fs/n are separated.

The separated angle modulated wave has the width fluctuation removed by a limiter circuit 15, and is demodulated by an angle demodulator 16 to become a luminance signal 11.

On the other hand, the separated color signal (frequency f8) and pilot signal (frequency fP) either pass through the pilot mixer 9 or turn off the power supplies related to 2, 3, 4, 5, 6, and 713 during reproduction. Since there is no output from the pilot signal oscillator 13, the pilot mixer 9 serves as a gate circuit that regeneratively passes the output of the low-pass filter 8.

This signal signal has jitter due to the uneven rotation of the rotating head 12 and the music (here, the jitter of the color signal f8 is △
f).

A low pass filter 20 carries the pilot signal.

Here, 20 may be a bandpass filter. The pilot signal extracted in this way is sent to the limiter circuit 21 to remove amplitude fluctuations, and then sent to the recording/playback switch 22 to receive the output b of the limiter circuit 21 instead of the output a of the pilot signal generator 13.
is passed through and multiplied by n in the n multiplier circuit 23.

A continuous wave having the same jitter as the color signal of frequency f8 output from this n-multiplying circuit and reproduced is produced.

Therefore, the signal is sent to the bandpass filter 26 output.

+f8+△f.

The frequency of this signal is converted by the frequency converter 17, and the signal passed through the bandpass filter 18 is a signal component. Here, from equation (9), the sudden signal (frequency f.

) is the jitter-cancelled signal, and equation (10) is the pilot signal within the color signal band (when n = 3, 4.0 9 M
Hz), the jitter remains by V3△f when n=3.

Equation (11) becomes Δf for the pilot signal (n-3) outside the color signal band and increases.

This means that the energy of the color signal with frequency fC is the second
As shown in the figure, fC, fo±fH, fo±2 f,...
It exists in ... and does not move because there is no jitter.It exists in a faint place (the valley of energy in Figure 2), and due to jitter, the frequency shifts slightly by 2/3△f,
Due to the comb effect, this value is completely acceptable.

In addition, in the case of equation (11), there are cases where the frequency fluctuation lights up at f8 and moves by 4/3△f, and the comb effect cannot be changed much, so in that case, the band of the bandpass filter 18 should be made slightly narrower. Bye.

This varies depending on the jitter of the VTR.

Even if it is narrow, 3. 5 8 MHz±500KHz is
The high frequency is 4.08 lVIHz, and the entire band can be covered.

In the main text explanation, the pilot signal oscillator 13 is a fixed oscillator, but 3. The pilot signal oscillator 13 is phase-synchronized with the input burst signal. 5 8
It goes without saying that it is also possible to create a continuous wave of MHz and multiply it by y/x.

In this way, the present invention records a pilot signal superimposed within the low-frequency conversion signal band, so that the magnetic recording and reproducing device can be used in as narrow a band as possible, and when reproducing, the pilot signal is extracted and the continuous wave signal is recorded. The pilot signal can be easily removed with a comb filter, so the S/ of the color signal can be
N is also improved, cross color can be removed, and since APC is not used, followability is good, residual errors are small, and a much more stable screen than the conventional pilot method can be provided.

In addition, in order to extract the pilot signal fP and increase the S/N, fP-2556 is added to the output of the low-pass filter 20 as shown in Figure 3.
If a signal delayed by one cycle corresponding to 81 KHz (one cycle delay) and a signal other than that are added together to improve the S/N ratio, a better screen will be obtained.

[Brief explanation of drawings]

Figure 1 is a recording spectrum diagram of conventional and text type, and Figure 2 is 3. 5 8 MHz signal energy distribution diagram, 3rd
The figure is a basic block diagram of the present invention, and FIG. 4 is a diagram showing signals after reproduction heterolog-in. 1...Input terminal, 2,8,20...Low pass filter, 3...Angle modulator, 4,14...
...High-pass filter, 6.18.26... Bandpass filter, 7.17.25... Frequency converter, 9... Pilot mixer, 10.・・・・・・
Mixer, 13... Pilot signal oscillator, 15
．． 21...IJ Mitsuta circuit, 23...
・Multiplier circuit, 19...comb-shaped filter.

Claims (1)

[Claims] 1. The brightness signal of the color television signal is angularly modulated on the high side, the carrier color signal with frequency fc is frequency-converted to the low frequency side with frequency f8, and both signals are mixed to produce a recording medium. In the low-pass conversion recording and reproducing method for recording and reproducing the above, (where fH is the horizontal synchronizing signal frequency and m is an integer), the pilot signal frequency fP is selected to be - (where n is an integer),
A magnetic recording/reproducing method characterized in that the pilot signal is superimposed and recorded within the carrier color signal band frequency-converted to the lower frequency side so that f8 and fP have an interleaving relationship.