KR900003111Y1 - Rf modulator with audio intercarrier frequency converter - Google Patents

Abstract

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Description

RF modulator with voice intercarrier frequency inverter

1 is a main circuit diagram of a voice intercarrier frequency conversion circuit of the present invention.

2 is a comparison diagram of pre-emphasis characteristics of different broadcasting schemes.

3 is a frequency characteristic diagram demodulated with different time constants of preemphasis deemphasis.

4 is a block diagram of a conventional RF modulator.

* Explanation of symbols for main parts of the drawings

1: Clamp Circuit 2: Modulator Mixer

3: buffer amplifier 4: voice oscillation modulator

5: tuning circuit 8: amplifier

6: video carrier oscillator circuit 7: attenuator

9 pre-emphasis circuit 10 switch element

11: tuning capacity 13-15: tuning coil

16: conversion switch of tuning coil 19: conversion circuit

21: capacity 22, 23: resistance

The present invention relates to an RF modulator for converting a video signal and an audio signal into an RF signal in a video tape recorder (hereinafter referred to as a VTR), and more particularly, to an RF modulator having a plurality of voice intercarrier frequencies for listening to different broadcasting schemes.

Since televisions have different broadcasting methods in different countries, different products are used in different RF modulators for converting video and audio signals, such as VTRs.

Therefore, especially in a region where a large number of neighboring stations, such as Europe, receives a different broadcast from a neighboring station, or when a device is exported to another country for use, it is necessary to replace the RF modulator each time. Suffer.

In addition, when receiving a large number of broadcast systems, the number of RF modulators must be purchased, so that the economic burden was large. However, the difference between the broadcast methods is that only the voice intercarrier frequency is different, and the RF modulator is provided with a means for selectively converting the voice intercarrier frequency, as shown in FIG.

In detail, the video signal input from the video signal input terminal T1 in FIG. 4 is applied to the modulator and the mixer 2 after passing through the clamp circuit 1. On the other hand, the voice signal input to the voice signal input terminal T2 is first applied to the pre-emphasis circuit 9, and amplified by the amplifier 8 to generate the voice oscillation, the modulator 4 and the tuning circuit 5. The signal is modulated into a voice intercarrier signal and applied to the modulator and the mixer 2 via the buffer amplifier 3. The modulator, the commercial signal applied to the mixer 2, and the modulated audio carrier signal are frequency-converted at the same time as modulating the carrier applied from the video carrier oscillation circuit 6, and the level is selected by the attenuator 7. It is output from the terminal. In the figure, the pre-emphasis circuit 9 is a circuit for emphasizing the high range of the signal in advance in order to improve the S / N ratio of the input audio signal. By appropriately setting the constant, a time constant corresponding to the desired broadcast method is obtained.

In the figure, the tuning circuit 5 connected to the voice oscillation and modulator 4 is connected to the tuning capacitor 11 via the first coil 13 and the conversion switch 16. It consists of the 2nd coil 14 and the 3rd coil 15 connected in parallel with 13).

Now, when the conversion switch 16 is OFF, that is, the position of ab, the voice intercarrier frequency of the first broadcasting system determined by the tuning capacitor 11 and the first coil 13, for example, the NT system M system. Tuned to 4.5MHz.

Next, when the changeover switch 16 is at the ac position, the second broadcasting method determines the tuning capacitor 11 and the first coil 13 and the second coil 14 in parallel. It is tuned to a voice intercarrier frequency, for example 5.5 MHz, which is the G scheme of PAL. Similarly, when the changeover switch 16 is at the position of ad, the third broadcasting method determines the tuning capacity 11, the first coil 13 and the third coil 15 to be a value connected in parallel. It is tuned to the voice intercarrier frequency of, for example, 6 MHz, which is the I system of PAL.

In the conventional RF modulator having a plurality of different broadcast system voice intercarrier frequency converters, only the voice intercarrier frequency is converted, and for example, the P system G system voice intercarrier frequency 5.5 MHz, I The values tuned to the respective frequencies of 6 MHz of the system and 4.5 MHz of the voice intercarrier frequency of the M system to the NTSC were only output to the conversion switch 16 of the tuning circuit 5 according to the selective output.

However, the PAL and NTSC voice conversion methods not only have different voice intercarrier frequencies but also different voice modulations. For example, the PAL method has a deflection of ± 50 Hz for 100% voice modulation, Since the time constant for the frequency characteristic correction by the sheath circuit is 50 Hz, the NTSC method has a deviation of ± 25 Hz and a time constant of 75 Hz, so that if the PAL method preemphasis circuit is used. As such, when the intercarrier frequency is converted, the voice modulation degree becomes deeper in the NTSC method.

When the frequency characteristics are compared with the reference frequency of 1 kHz, as shown in the graph of FIG. 2, there is a difference in the emphasis characteristics, and the amplitude characteristics after modulating the speech frequency with the speech frequency by a different emphasis circuit in FIG. As shown in Fig. 1, the high frequency is reduced, so the intelligibility of speech is reduced when switching from PAL to NTSC.

The present invention, in view of the above-mentioned conventional problems, the voice intercarrier frequency for selectively outputting the voice intercarrier frequencies of a plurality of different broadcast method by the conversion switch in the RF modulator for converting the video signal and the audio signal into the RF signal In an RF modulator having a conversion device, a switch of a conversion switch 16 for converting a voice broadcasting carrier frequency to a conversion to a different broadcasting system and a conversion circuit 19 for converting a time constant of the voice prefix circuit 9 are used. The configuration is linked.

The above technical means function as follows. In other words, the PAL is switched by a switch of the conversion circuit 19 for switching the time constant of the pre-emphasis circuit 9 in the audio signal processing section of the RF modulator of FIG. By converting 50 kHz and 75 kHz for NTSC, the voice frequency characteristics of both PAL and NTSC are smoothed to the high range.

Hereinafter, the present invention will be described in detail with reference to the drawings.

1 is a main configuration diagram showing an embodiment of the present invention.

The same parts as those in Fig. 4 of the conventional example are denoted by the same reference numerals and detailed description thereof will be omitted.

First of all, in the pre-emphasis circuit 9, the switch element 10 is coupled to both ends of the resistor 23 connected in series with the resistor 22, and the switch element 10 is a conversion circuit. This conversion circuit 19 is configured to cooperate with a conversion switch 16 that selects a value tuned to, for example, a three-way intercarrier frequency of the tuning circuit 5.

For example, when the conversion switch 16 of the tuning circuit 5 is set to the position ab, that is, when the NT system M method selects a value tuned to a voice intercarrier frequency of 4.5 MHz, the conversion circuit 19 ef is an open position, and the switch element 10 is in an open state. Thus, the pre-emphasis circuit 9 has a capacitor 21 applied in parallel to a value in which the resistor 22 and the resistor 23 are connected in series. Since it is a composite value, by setting this value to 75 kHz, which is a time constant specified by the NTCS method, the voice intercarrier frequency and time constant can be simultaneously converted into a value matched by the NTCS method.

Next, when the conversion switch 16 of the tuning circuit 5 is set to the ac position, that is, when a value is tuned to the voice intercarrier frequency of 5.5 MHz of the PAL-G system, the conversion circuit 19 simultaneously operates. eg, the switch element 10 is turned on, so that the voice intercarrier frequency and time constant can be simultaneously converted into values consistent with the PAL method.

Next, when the conversion switch 16 of the tuning circuit 5 is set to the ac position, that is, when a value tuned to the 5.5 MHz voice intercarrier frequency of the PAL-G system is selected, the conversion circuit 19 simultaneously operates. eg, the position of eg is turned ON, and since the switch element 10 conducts, both ends of the resistor 23 of the pre-emphasis circuit 9 become short-circuited, and the cryogenic value of the resistor 22 and the capacitor 21 Since this is a parallel list, by setting this value to 50 ms of time constants specified in the PAL method, the voice intercarrier frequency and time constant can be simultaneously converted into values consistent with the PAL-G method.

When the conversion switch 16 is set to the ad value, the conversion circuit 19 becomes the ON position of the eh, and the switch element 10 is turned on, so that the voice intercarrier frequency and the time constant are simultaneously controlled in the PAL mode. Can be converted to a matched value.

In this configuration, the tuning circuit conversion switch 16 of the voice intercarrier frequency is used as a mechanical switch of three circuits, and the conversion circuit 19 interoperating with the switch is similarly a mechanical switch of three circuits. 10) is composed of a semiconductor, but of course, other combinations are possible. For example, it is also conceivable that the conversion of the voice intercarrier frequency and time constant is composed of a semiconductor element, and also the voice intercarrier frequency and visibility. The conversion of numbers can be performed without using a semiconductor device by using a mechanical switch of two circuits and three contacts.

As described above, the present invention is an RF modulator for selectively outputting voice intercarrier frequencies of a plurality of different broadcasting methods, and simultaneously the time constant of the voice preemphasis circuit in conjunction with converting the voice intercarrier frequencies to different broadcasting methods. Since the conversion is possible, the frequency becomes flat even when the audio frequency of any broadcasting system is reproduced, and defects in the conversion of the conventional broadcasting system, for example, the PAL system and the NTCS system, are used. When the conversion is performed, problems such as high frequency drop and voice intelligibility decrease, which cannot be tolerated in music observation, are solved. Thus, it is possible to obtain Hi-Fi sound in any broadcasting system.

Claims (1)

An RF modulator for selectively outputting audio intercarrier frequencies of a plurality of different broadcasting methods by converting switches to convert a video signal and an audio signal into an RF signal, wherein the audio intercarrier frequencies are converted for conversion to a desired broadcasting method. An RF modulator having a voice intercarrier frequency converter, characterized in that the conversion switch 16 and the conversion circuit 19 for converting the time constant of the voice prefix circuit are interlocked.