JPS60121886A - Magnetic video-recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent excess modulation of an amplitude modulator by limiting a level of an image signal which is impressed on the amplitude modulator only for the period when the noise due to tracking dislocation at the time of reproduction occurs. CONSTITUTION:After a reproduced frequency modulation image signal from a rotational magnetic head 1 is demodulated by a frequency demodulator 2, the signal is supplied to an amplitude modulator 5 through a clamp circuit 3 and a clip circuit 4. On the other hand, a part of the output of the demodulator 2 is supplied to a drop-out detection circuit 6, and when the level of the reproduced frequency modulation image signal becomes a prescribed level or below, a drop- out detection signal which indicates the drop-out period is generated. The detection signal is impressed on the clip circuit 4 as the control signal through a gate circuit 8 which conducts by the output of a special reproduction mode indicating circuit 7. Therefore, the clip circuit 4 executes the clip operation only when the drop-out detection signal exists. Thus, the excess modulation of the amplitude modulator can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a helical scan type rotary head type magnetic recording and reproducing apparatus (hereinafter abbreviated as VTR).

As is well known, when playing back a helical scan VTR,
By playing back at a tape speed different from the tape speed at the time of recording, it is possible to play back as a slow motion image or quick motion image. However, in such special playback conditions, the scanning trajectory of the playback head and the recording trajectory do not match, so noise occurs during periods when the scanning trajectory during the recording trajectory sub- and f-choice periods is significantly different, and the reproduced image is affected by noise. The signal level has become so great that an RF converter can instantly convert the reproduced video signal into a broadcast wave of a predetermined channel (AM
There was a problem that over-modulation occurred when the signal was modulated (modulation), causing buzz in the television receiver.

The present invention provides a means for solving this problem, and one implementation thereof will be described below with reference to the drawings.

In the drawing, reference numeral 1 denotes a rotating magnetic head of a VTR, and a frequency-modulated video signal reproduced from the rotating magnetic head 1 is demodulated by a frequency demodulator 2, and then sent to a clamp circuit 3. The signal is inputted via a clip circuit (suppression circuit) 4 to an amplitude modulator 5 that constitutes an RF converter. The signal converted into a broadcast wave of a predetermined channel by the amplitude modulator 5 is applied to a television receiver.

On the other hand, a part of the frequency-modulated reproduced video signal from the rotating magnetic head 1 is input to a conventionally known dropout detection circuit 6 consisting of an envelope detection circuit or the like, and the level of the reproduced frequency-modulated video signal is determined to be below a predetermined level. Obtain a dropout detection signal indicating a dropout period.

This dropout detection signal is a gate circuit that becomes conductive due to the output from the special square mode instruction circuit 7 only when a special tape speed is played back at a tape speed different from the tape speed during recording, such as slow motion playback or quick playback. 8 to the clip circuit 4 as an open side 1 signal. This clipping circuit 4 performs a clipping operation only when the dropout detection signal exists, and
AM as a signal below the level at which the modulator 6 causes overmodulation.
This is what leads to the modulator.

Generally, when a clip circuit attempts to cut off a signal above a certain level, signals near that level are also distorted.

Therefore, it is convenient to perform the clipping operation only during the dropout period as in this configuration.

Further, instead of the clip circuit, an attenuator that increases the attenuation rate only during the dropout period or an amplifier that decreases the amplification rate may be used.

As described above, according to the present invention, the AM
Since it is configured to limit the video signal level applied to the modulator, it is always level 1ljll even during the normal operation period.Compared to the above, the video signal level during the normal operation period is The negative effects are permanent.

[Brief explanation of the drawing]

The drawing is a block diagram of essential parts showing an embodiment of the magnetic recording and reproducing apparatus of the present invention. 1... Rotating magnetic head, 2... Frequency demodulator. 3... Clamp circuit, 4... Clip circuit, 6... Width variation JM device, 6... Dropout detection circuit, 7... Special playback mode instruction circuit,
8...Gate circuit.

Claims (1)

[Claims] (1) A magnetic recording and reproducing device that demodulates the full frequency of a frequency modulated video signal reproduced by a rotating magnetic head, and then modulates the amplitude with an amplitude modulator and converts it into a broadcast wave, wherein the envelope of the reproduced frequency modulated video signal is [d]
4? configured to apply to the modulator? A magnetic recording and reproducing device.