JPH024544Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video tape recorder having a television tuner and an RF modulator for receiving television audio multiplex broadcasts.

BACKGROUND ART AND PROBLEMS First, a conventional RF modulator for a video tape recorder will be described with reference to FIG. 1
2 shows the RF modulator as a whole, in which a video signal (synthesized video signal) from a TV tuner (not shown) that receives TV audio multiplex broadcasting and 2-channel audio signals are connected to the video signal input terminal 2 and the left and right audio signal input terminals 3L, respectively. , 3R.
Two channels of audio signals from input terminals 3L and 3R are supplied to an adder 4 and a subtracter 5, respectively. A signal representing the difference between the left and right audio signals is obtained from the subtracter 5,
This passes through the low-pass filter 6 to the FM modulator 7.
supplied to On the other hand, an audio signal that is the sum of the left and right audio signals is obtained from the adder 4, and this is supplied to the pre-emphasis circuit 10 via the low-pass filter 9. Then, in the stereo mode, the FM modulated difference audio signal obtained from the FM modulator 7 and the sum audio signal obtained from the pre-emphasis circuit 10 are supplied to the adder 8 and added. Such addition is not performed, and only the sum audio signal is output from the adder 8. Furthermore, in stereo mode, the pilot signal from the pilot signal generating circuit 12 is also added to both signals in the adder 8. The output signal from adder 8 is supplied to FM modulator 13. Then, the video signal from the video signal input terminal 2 (composite video signal including a synchronization signal) and the FM modulated composite audio signal from the FM modulator 13 are supplied to the adder 14 and added, and then AM modulated. is supplied to the container 15. Output terminal 16
A high-frequency composite video signal of the carrier frequency of an empty channel such as TV channel 2 or channel 1 is obtained from the TV, and this is sent to the coaxial cable, feeder, etc. led out from the antenna via a TV/VTR switch (not shown). connected to.

11 is a stereo/monaural switching control signal input terminal for two-channel audio signals;
This input terminal 11 is grounded through a manual stereo/monaural changeover switch (on/off switch) SW. A switching control signal from a switching control signal input terminal 11 is supplied to an FM modulator 7 and a pilot signal generator 12.

Next, the operation of a video tape recorder including such an RF modulator will be explained. When the changeover switch SW is turned on, the RF modulator 1 is switched to the stereo state. Therefore, the FM modulator 7 is activated, and the pilot signal generation circuit 12 is activated.
A pilot signal is generated from In this way, when the left and right audio signals are supplied to the audio signal input terminals 3L and 3R, respectively, an FM modulated signal of the difference between the left and right audio signals is obtained from the FM modulator 7, and the pilot signal generation circuit Pilot signals are obtained from 12, these signals are summed with the sum audio signal from pre-emphasis circuit 10 and supplied to FM modulator 13. Then, the FM modulated synthesized audio signal obtained from this is added to the video signal from the input terminal 2 in the adder 14, and then the AM
A high frequency composite video signal having a stereo audio signal at an output terminal 16 is obtained by being supplied to a modulator 15 . In this case, the audio signal input terminals 3L, 3
When the signal supplied to R is a monaural audio signal, the FM modulated synthesized audio signal from the FM modulator 13 becomes a signal containing the monaural audio signal and the pilot signal, and is transmitted to the television connected to the video tape recorder. In the monitor receiver, the stereo pilot lamp is lit, but essentially a monaural audio signal is reproduced.

Further, when a monaural audio signal is supplied to the audio input terminals 3L and 3R, the changeover switch SW is turned off. In this case, the FM modulator 7 does not operate, and furthermore, the pilot signal generating circuit 12 does not generate a pilot signal. For this reason, only the sum audio signal from the pre-emphasis circuit 10 is supplied to the FM modulator 13, and the FM modulated synthesized audio signal including the obtained monaural audio signal is added to the video signal from the input terminal 2 to perform AM modulation. is supplied to the container 15. In this case, the audio signal input terminal 3L,
Even though the audio signals supplied to the adder 4 are left and right audio signals, when turning off the changeover switch SW, the audio signal input terminals 3L and 3 in the adder 4 are
Only the summed output of the left and right audio signals from R is supplied to the FM modulator 13, and is treated as a monaural mode.

Incidentally, in such a video tape recorder, a television tuner built into the video tape recorder is often used to receive television broadcasts on a television monitor receiver.

By the way, in this case, when the electric field is strong, the switch SW is turned on to put the RF modulator in the stereo state, and when the electric field is weak, the switch SW is turned on.
I often turn off the RF modulator and play it in monaural mode. The same thing can be said when recording.

By the way, in places with weak electric fields, the RF modulator is normally set to monaural by switching the switch SW, so when playing back a videotape with stereo audio recording, it is necessary to switch the switch SW and set the RF modulator to monaural mode. The modulator is placed in a stereo state. However, this is complicated to operate and requires a switch.
If you forget to switch the SW, even video tapes with stereo audio recording will be played back in monaural.

Purpose of the invention In view of the above, the present invention provides a videotape in which the RF modulator is automatically switched to stereo during playback even if the RF modulator is switched to monaural when receiving or recording audio multiplex television broadcasting. This is an attempt to propose a recorder.

Summary of the invention The present invention provides a first channel audio signal and a second channel audio signal.
In a video tape recorder equipped with an RF modulator that receives an audio signal and a video signal of a channel and generates an audio multiplexed television high-frequency signal from them, the RF modulator has a first a first FM modulator that performs FM modulation on the difference signal of the second channel audio signal;
a pilot signal generation circuit; an adder for adding the output of the first FM modulator and the pilot signal from the pilot signal generation circuit to the sum signal of the respective audio signals of the two channels; and an adder for FM modulating the added output. In addition to providing a second FM modulator, a control terminal is provided that can be operated by a manual switch installed on the video tape recorder to stop the output of the pilot signal applied to the adder, and a transistor switch connected to this control terminal is The tape recorder is controlled during playback so that the output of the pilot signal is supplied to the adder in the playback mode, regardless of the switching state of the manual switch.

According to the present invention, regardless of the switching state of the manual stereo/monaural changeover switch connected to the RF modulator, in the playback mode,
It is possible to obtain a video tape recorder whose RF modulator can automatically switch to stereo.

Embodiment An embodiment of the present invention will be described below with reference to FIG. 2. In FIG. 2, parts corresponding to those in FIG. Second
In the video tape recorder shown in the figure, a switching transistor 17 serving as an automatic stereo/monaural changeover switch is connected to the stereo/monaural changeover control signal input terminal 11. That is, the collector of the transistor 17 is connected to the input terminal 11, and its emitter is grounded. Further, the base of the transistor 17 is grounded through a resistor 18, and connected through a resistor 19 to an input terminal 20 to which a reproduction mode signal from a system controller (not shown) is supplied.

Next, the operation of the video tape recorder shown in FIG. 2 will be explained. Here, only the operations different from those of the video tape recorder shown in FIG. 1 will be explained. In the playback mode, a playback mode signal from the system controller is supplied to the input terminal 20, the transistor 17 is turned on, and the input terminal 11 is grounded regardless of whether the manual stereo/monaural changeover switch is on or off. Therefore, the FM modulator 7 is activated, and the pilot signal generation circuit 12 is activated.
A pilot signal is generated from the RF modulator 1, and the RF modulator 1 automatically enters the stereo state.

Therefore, if a video cassette tape recording stereo sound is loaded into a tape recorder and played back, the stereo sound will be played back along with the video from the television monitor receiver.

Some video cassette tapes have monaural audio recorded, but even in this case, the stereo pilot lamp on the TV monitor will light up, but the monaural audio signal will be played back from the left and right speakers, so there will be no auditory distortion. There is no profit.

Effects of the invention According to the invention described above, regardless of the switching state of the manual stereo/monaural changeover switch,
A videotape recorder can be obtained in which the RF modulator can automatically switch to stereo when in playback mode.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an RF modulator of a conventional video tape recorder, and FIG. 2 is a block diagram showing an embodiment of the video tape recorder according to the present invention. 1 is RF modulator, SW is manual stereo/
11 is a stereo/monaural switching control signal input terminal, and 17 is a switching transistor serving as an automatic stereo/monaural switching switch.

Claims (1)

[Scope of utility model registration request] A video tape recorder is equipped with an RF modulator that receives the audio signal of the first channel, the audio signal of the second channel, and the video signal and generates an audio multiplexed television high-frequency signal from these signals. The RF modulator includes a first FM modulator that performs FM modulation on a difference signal between the audio signals of the first and second channels, a pilot signal generation circuit, and a sum of the audio signals of the two channels. The video tape recorder is provided with an adder for adding the output of the first FM modulator and the pilot signal from the pilot signal generation circuit to the signal, and a second FM modulator for FM modulating the added output. A control terminal is provided which can be operated by a manual switch provided to stop the output of the pilot signal applied to the adder, and furthermore, a transistor switch connected to this control terminal is controlled during playback of the video tape recorder to control the operation of the manual switch. A video tape recorder characterized in that the output of the pilot signal is supplied to the adder in the playback mode regardless of the switching state.