JPS582406B2 - Jikiki Rokusai Seisouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing device in which video signals are recorded and reproduced by a rotating magnetic head that is in contact with a magnetic sheet. This is to prevent this from occurring.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 1 indicates a hollow cylindrical drum driven in the direction of the arrow at 30 revolutions per second, and 2 indicates its rotation axis. , 3A and 3B indicate two rotary magnetic heads that rotate together with the drum 1, one rotary magnetic head 3A is used for recording and reproduction, and the other rotary magnetic head 3B is used for reproduction.

The magnetic heads 3A and 3B are opposed to each other with an angular interval slightly different from 180° so as not to cause disturbance in the horizontal synchronizing signal during reproduction, which will be described later.

Further, 4 indicates a semi-cylindrical guide body facing the outer peripheral surface of the drum 1, and a locking piece 6 is fixed to one end surface of the guide body 4.
A magnetic sheet 5 is inserted from the other end side into the gap formed by the outer peripheral surface of the drum 1 and the inner peripheral surface of the guide body 4, and this magnetic sheet 5 is attached to the drum 1 within an angular range of approximately approximately 180°. Surrounded by

The magnetic sheet 5 is moved in a direction parallel to the rotating shaft 2.

Therefore, as the rotating magnetic head 3A scans as shown by the arrow Y in FIG. 2, and the magnetic sheet 5 moves as shown by the arrow X, sequentially inclined tracks T are formed on the magnetic sheet 5. will be done.

Furthermore, to explain in detail, in this example, the rotating magnetic heads 3A and 3
The gap width of B, that is, the scanning width d is, for example, 3 of the track width P.
Selected twice.

As will be described later, recording of the phase-modulated video signal is performed only by the rotating magnetic head 3A rotating at 30 revolutions per second, so that the input signal shown in FIG. By skipping, for example, odd fields 1f, 3f, 5f, . . . are recorded.

Recording by the rotating magnetic head 3A is started from the lower side of the magnetic sheet 5, and as shown in FIG.
The signal of the field 1f is recorded, and then the rotary magnetic head 3A rotates once and the magnetic sheet 5 is moved by the track width P until it comes into contact with the lower side of the magnetic sheet 5 again. The signal 3f is overlapped with the track where the signal of the first field 1f is recorded, leaving only the track width P, and finally a track T1 where the signal of the first field 1f is recorded is formed.

Thereafter, in the same manner, the third field 3f, the fifth field 5f, etc. are recorded on tracks T2 and T.
3... is formed.

As a result of this field skip recording, each track T1, T2, T3,
The vertical synchronizing signal (shown with diagonal lines) (2) and the horizontal synchronizing signal H can be arranged in a straight line.

When reproducing such a magnetic sheet 5, the rotating magnetic head 3A
and 3B are used, and the rotational speed and the moving speed of the magnetic sheet 5 are the same as during recording, so that the gap ga of the rotating magnetic head 3A is the same as that of the tracks T1, T2 and T2 as shown in FIG. T3 is scanned, and then the rotating magnetic head 3
Gap gb of B is half of track T1 and track T2
Then, the gap ga of the rotary magnetic head 3A scans half of the tracks T3 and T4, and then the gap ga of the rotating magnetic head 3A scans half of the tracks T3 and T4.
, T3 and T4, and similar positions are scanned thereafter.

As mentioned above, each track T1, T2......
Since the signals of the odd fields if, 3f, .

For example, by scanning tracks T1, T2, and T3, one field's worth of signals in which the signals of the first field 1f, the third field 3f, and the fifth field 5f are mixed,
You can get a raw signal.

Generally, the images of each field from the first field 1f to the fifth field 5f are not significantly different, and the synchronization signals are aligned, so the reproduced and demodulated video signals can be high-frequency modulated and viewed on a monitor receiver. I can do it.

By the way, when a video signal is FM modulated and recorded on the magnetic sheet 5 as in a conventional magnetic recording/reproducing device, for example, when tracks T1, T2, and T3 are simultaneously reproduced, the signals are reproduced from each track. the first field 1f,
There is a drawback that a beat occurs between the signals of the third field 3f and the fifth field 5f, resulting in a deterioration of the S/N ratio.

In the present invention, in order to prevent S/N from deteriorating, the video signal is phase modulated and the phases of the carrier wave components are matched between adjacent tracks.

That is, as shown in FIG. 7, the video signal from the input terminal I is supplied to the phase modulator 8, the carrier wave from the oscillator 9 is phase modulated, and the modulated signal is transmitted through the recording side contact R of the switch 10. It is supplied to the recording rotary magnetic head 3A and recorded on the sheet 5 as described above.

Then, during reproduction, the reproduction outputs from the reproduction magnetic heads 3A and 3B are combined, passed through a reproduction amplifier 11, and supplied to a demodulator 13 through a limiter 12 for demodulation, and a demodulated output is obtained at an output terminal 14.

In this case, by synchronizing the oscillator 9 with the rotation of the seat 5, the phase of the carrier wave modulated as shown by the broken line in FIG.
n+1..., so that they match at the same rotation angle position, and the modulation index m in phase modulation is 1,
Make sure it is 3 or less.

The modulation index m in phase modulation is expressed by the amount of phase displacement of the modulated wave with respect to the carrier wave in radians,
Of course, it changes depending on the value of the modulated wave at each point in time.

Therefore, setting the modulation index m to be 1.3 or less means performing phase modulation such that the phase displacement amount is 1.3 radians at maximum.

By the way, the phase modulated wave is carrier wave J.

and upper and lower sideband waves J1, J of first, second, third...
2, J3, .

Therefore, when the modulation index m is set to 1.3 or less, the secondary and higher order sideband components become sufficiently small that they can be ignored.
Also carrier wave J.

The amplitude of can be considered to be approximately constant regardless of the value of the modulation index beat, that is, regardless of the value at each point in time of the modulation wave.

That is, the phase of the composite wave J of the first-order upper and lower sideband waves is always the carrier wave J.

The phase will be shifted by 90°, but this 90°
The amplitude of the shifted primary sideband wave J1 changes as shown in FIG. 9 according to the value of the modulated wave at each point in time, resulting in a carrier wave J.

This means that the amount of phase displacement of the modulated wave as a composite wave of the primary sideband wave J1 with respect to the carrier wave is changing.

Therefore, as shown in FIG. 8, the gap g of the rotating magnetic head is
If the center position Z of track Tn is shifted from the center position 0 of track Tn by
X) and scans with a width X over track Tn-2, thus carrier wave J in tracks Tn-2, Tn-1, Tn and Tn+1.

As described above, the carrier wave component J in the reproduced signal from the rotating magnetic head is recorded so that the same amplitude and phase match in adjacent tracks.

As is clear from Figure 10, the amplitude of becomes.

Therefore, no matter where the rotating magnetic head is located, the amplitude of the carrier wave component remains approximately constant.

This holds true not only when the relationship (d=3p) is satisfied, but in general.

On the other hand, each track Tn-2, Tn-1, Tn and Tn+
As mentioned above, the amplitude of the primary sideband wave J1 in J, (n- 2),
Since it is expressed as J1 (n-1), Jt (n), and Jx (n+1), the amplitude of the primary sideband component in the reproduced signal from the rotating magnetic head is, as is clear from Fig. 10, as follows. expressed.

Therefore, when the video signals, which are modulated waves corresponding to each track, are phase-modulated separately and synthesized at a level ratio of K:1:1:K2, the playback output for each track is Tn-2, Tn-1,
K1 is the video signal which is a modulated wave corresponding to Tn and Tn+1.
:1:1:K2 level ratio and almost equal to phase modulation.

Therefore, if this playback output is demodulated as described above, the demodulated output will be the original, ie, unmodulated, video signal corresponding to each track Tn-2, Tn-1, Tn, and Tn+1 in a predetermined manner according to the position of the rotating magnetic head. It becomes almost equal to that synthesized with the level ratio of , and it is possible to prevent noise such as beat disturbance from occurring.

In this case, the reproduced signal is obtained by sequentially synthesizing the signals of a plurality of adjacent frames, but since the content of the image generally does not change significantly, this point is not as problematic in practice.

Since a predetermined reproduced video signal can be obtained even if the gap g of the rotary magnetic head is misaligned, so-called tracking servo during reproduction is not required, and since no interval is formed between each track, the recording density is increased.

As is clear from FIG. 9, as the modulation index m increases, the carrier wave component J in the modulated wave increases.

The amplitude gradually decreases and can no longer be regarded as constant, and therefore, the value at each point in time of the video signal, which is a modulated wave, and the amplitude of the primary sideband no longer correspond linearly.

Therefore, the modulation index m is set in the range of 1.3 (75° in terms of angle) or less as described above.

It is also possible to record the video signal by amplitude modulating it, but
In this case, the S/N ratio deteriorates because so-called AM noise is generated due to amplitude fluctuations caused by passing through the magnetic medium or the magnetic head thread.

In the case of phase modulation as in the present invention, this amplitude fluctuation can be removed by supplying the reproduced signal to the demodulator through the limiter as described above.

In the case of a color video signal, the luminance signal is phase-modulated and recorded as described above, and the carrier color signal whose subcarrier is amplitude-modulated by the red and blue color difference signals is frequency-converted to the lower frequency side. Then, recording may be performed so that the phase of the converted subcarrier wave coincides with that of the carrier wave in phase modulation at the point where the air gap of the reproducing head is located at the same time in each track.

[Brief explanation of drawings]

Fig. 1 is a sectional view of essential parts of an embodiment of the present invention, Fig. 2 is a plan view of an example of a magnetic sheet, Fig. 3 is a schematic diagram showing the recording state, and Fig. 4 is an image during recording and reproduction. A schematic diagram used to explain the signal, Figure 5 is a partially enlarged view of a track formed on a magnetic sheet, Figure 6 is a diagram showing the scanning state during reproduction, and Figure 7 is a circuit system connection. 8 are partially enlarged views of tracks formed on the magnetic sheet, and FIGS. 9 and 10 are schematic diagrams for explaining the state of phase modulation. 2 is a rotating shaft, 3A and 3B are rotating magnetic heads, and 5 is a magnetic sheet.

Claims (1)

[Claims] 1 A magnetic sheet is wound over an angular range of 180° or more around a drum containing two rotating magnetic heads separated by an angular interval of approximately 180°, and the upper rotating magnetic head rotates at a speed of 1 rotation in 2 fields. At the same time, the magnetic sheet is relatively moved in the direction of the rotation axis of the rotary magnetic head at a predetermined speed, and during recording, one rotary magnetic head is used to record data with a modulation index of 1.3 or less. Every other field of the phase modulated video signal forms a track on the magnetic sheet with no gaps between adjacent ones, and the recording positions of the vertical synchronization signal and the horizontal synchronization signal are aligned in a straight line. In addition, recording is performed so that the phase of the carrier wave to be modulated is aligned in each track, and during reproduction, the two rotating magnetic heads alternately reproduce the tracks with a scanning width sufficiently larger than the width of the two rotating magnetic heads. magnetic recording and reproducing device.