JPS622849Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a television signal transmitter, in which a filter circuit is provided in the input signal transmission line system of an amplitude modulator to make the audio subcarrier in the UHF band or higher band. An object of the present invention is to provide a television signal transmitter that can reduce spurious audio interference imparted to adjacent channels of a television receiver.

FIG. 1 shows a block diagram of an example of a conventional television signal transmitter. In the figure, 1 is an audio signal input terminal, and 2 is a video signal input terminal. The audio signal input from the audio signal input terminal 1 is supplied as a modulation signal to the audio subcarrier modulator 3, where it is converted into a subcarrier of a predetermined frequency from the subcarrier oscillator 4.
Modulate _s . The audio subcarrier, which is a modulated wave, extracted from the audio subcarrier modulator 3 is supplied to the amplitude modulator 5.

On the other hand, the video signal (either color or black and white) input from the video signal input terminal 2 is
After the pedestal level is clamped by the clamp circuit 6, it is supplied to the amplitude modulator 7. The amplitude modulators 5 and 7 are each supplied with the same main carrier wave of frequency _c from the main carrier oscillator 8, and each amplitude modulates the audio subcarrier from the audio subcarrier modulator 3 and the video signal from the clamp circuit 6. (converts the frequency) into a VHF band or UHF band signal.
VHF band or UHF band audio subcarrier from amplitude modulator 5 and video carrier frequency from amplitude modulator 7
The video carrier waves in the VHF band or UHF band shown in _c are each supplied to an adder 9, where they are frequency-division multiplexed and made into a television signal, which is then applied from an output terminal 10 to an antenna terminal of a television receiver, for example. .

Such conventional television signal transmitters are used to reproduce and display video and audio signals recorded on recording media such as magnetic tapes and disks on conventional television receivers, or are used in television game devices. However, as is clear from the configuration shown in Figure 1, if there is distortion in the audio subcarrier, the main carrier frequency _c
Sidebands of the carrier wave as shown in Fig. 2 are generated around , and among these, higher-order sidebands of _c ±2 _s , _c ±3 _s , etc. act as spurious waves that interfere with adjacent channels of the television receiver. give.

Conventionally, therefore, the spurious components are attenuated and removed from the television signal from the output terminal 10 using a bandpass filter before being transmitted. However, the above-mentioned bandpass filter is not suitable for television signals.
It is used only when transmitting in the VHF band, and is not used when transmitting in the UHF band because band filters that can sufficiently attenuate high frequency components such as those in the UHF band could not be manufactured. ,
Therefore, there was a drawback that the spurious components of the voice could not be removed.

The present invention has been made to eliminate the above-mentioned drawbacks, and various embodiments thereof will be described below with reference to Figs. 3 to 5.

FIG. 3 shows a block system diagram of a first embodiment of the television signal transmitter according to the present invention. In the same figure,
Components that are the same as those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted. In Fig. 3, 11 is a bandpass filter, which has a passband width of approximately _s ±300kHz (provided that _s is several MHz). This band filter 11 allows the frequency of the subcarrier oscillator 4 to be
The frequency component of _2s contained in the signal of _s is attenuated by about 50 dB or more than the output signal frequency _c of the main carrier oscillator 8 and is supplied to the audio subcarrier amplitude modulator 12. The audio subcarrier amplitude modulator 12 amplitude modulates the subcarrier of frequency _s from the bandpass filter 11 using the audio signal from the input terminal 1, and outputs this as an audio subcarrier to the amplitude modulator 5.

As a result, even if the audio subcarrier is distorted, the carrier in the output signal of the amplitude modulator 5 shows a frequency spectrum as shown in FIG. 4, and the main carrier
The level of _c ± 2 _s is attenuated by about 50 dB or more compared to _c , resulting in audio spurious _c ±
_2s can be considered to have been practically eliminated. This is 2 _s by the above bandpass filter 11.
This is because the frequency components of

In this way, according to this embodiment, a UHF band television signal in which the audio subcarrier is an amplitude modulated wave (for example, the audio subcarrier frequency _s is 6.5MHz)
A SECAM color television signal) is transmitted from the output terminal 13.

In the above embodiment, since it is sufficient to significantly attenuate the frequency component of 2 _s , a low-pass filter with a cutoff frequency of about _s + 300 kHz may be used in place of the band filter 11, and the band filter 11 or the above-mentioned A configuration may also be adopted in which a low-pass filter is inserted between the audio subcarrier amplitude modulator 12 and the amplitude modulator 5.

Next, a second embodiment of the television signal transmitter according to the present invention will be described with reference to FIG. FIG. 5 is a block system diagram of a second embodiment of the television signal transmitter according to the present invention, in which the same parts as in FIG. In FIG. 5, reference numeral 14 denotes an audio subcarrier frequency modulator, which outputs an audio subcarrier obtained by frequency modulating a carrier wave of a frequency _s using the audio signal from the input terminal 1. This audio subcarrier wave is passed by a band filter 15 having a pass band width of about _s ±300 kHz, and the audio subcarrier wave with _{a carrier frequency s is} passed through.
Each carrier wave _s , 3 _s , ... is here for _s
It is attenuated by about 50dB or more.

The output audio subcarrier of this band filter 15 becomes an audio carrier in the UHF band by amplitude modulating the main carrier frequency _c by the amplitude modulator 5. Also in this embodiment, the output signal of the amplitude modulator 5 The frequency spectrum of each carrier wave is as shown in FIG. 4, and by providing the bandpass filter 15, the spurious signal _c ± _2s is attenuated by about 50 dB or more with respect to the level of _c .

The audio subcarrier of carrier frequency _c + _s (or _c - _s ) is here a frequency modulated wave, and is frequency division multiplexed with the video signal of video carrier frequency _c in adder 9 to produce a television signal (for example, _s is a frequency modulated wave). The signal is transmitted from the output terminal 16 as a 4.5MHz NTSC color video signal).

Next, a third embodiment of the television signal transmitter according to the present invention will be described with reference to FIG. FIG. 6 shows a block system diagram of a third embodiment of the television signal transmitter according to the present invention, and the same parts as in FIG. 5 are given the same reference numerals, and their explanation will be omitted. 6th
In the figure, 17 is a luminance signal input terminal, and 18 is a carrier color signal input terminal. The luminance signal input from the input terminal 17 is supplied to the adder 18, where it is added and synthesized with the audio subcarrier of the carrier frequency _s from the bandpass filter 15, which is the main part of the present invention explained in conjunction with FIG. After that, the signal is supplied to the amplitude modulator 19. This amplitude modulator 19 modulates the amplitude of the main carrier wave from the main carrier wave oscillator 8 with a frequency division multiplexed signal consisting of the audio subcarrier and the luminance signal from the adder 18, thereby converting this frequency division multiplexed signal into the UHF band. The frequency is converted and the signal is supplied to the adder 9.

On the other hand, a carrier color signal having a color subcarrier frequency of 3.58 MHz, for example, inputted from the input terminal 18 is supplied to an amplitude modulator 20, where the main carrier oscillator 8
The main carrier wave is amplitude-modulated, frequency-converted to the UHF band, and then supplied to the adder 9. As a result, the brightness signal from the amplitude modulator 19 and the carrier color signal from the amplitude modulator 20 are band-sharing multiplexed by the adder 9, and these are frequency-division multiplexed onto the audio subcarrier from the amplitude modulator 19. The resulting color television signal is taken out and sent to the output terminal 21.
Sent from

In the case of this embodiment as well, as in each of the above embodiments, the band filter 15 causes spurious _c ±2 _s.
is attenuated by about 50 dB or more with respect to the level of _c .

In addition, in the second and third embodiments described above, even if a low-pass filter with a cutoff frequency of approximately _s + 300kHz is used in place of the bandpass filter 15, the
It can significantly attenuate harmonics above _s .

The above band filters 11 and 15 are 6.5MHz or
It is extremely easy to manufacture because it allows signals of several MHz such as 4.5 MHz to pass through and attenuates its second and higher harmonics. In addition, a bandpass filter 1 is provided in the input signal transmission line system of the amplitude modulator 5.
1 and 15 to reduce the harmonics of _s that cause spurious in advance, and then transmit the audio subcarrier to UHF.
I am trying to convert the frequency into a band. Therefore,
It can reduce and eliminate audio spurious noises that interfere with adjacent channels of UHF television receivers.

Note that in each of the above embodiments, a case was explained in which a UHF band television signal was transmitted.
In principle, it is also possible to apply the present invention to the case where a television signal is transmitted after being converted to a high frequency band higher than the UHF band.

As described above, the television signal transmitter according to the present invention transmits at least an audio subcarrier to the input signal transmission line system of a circuit for frequency converting the audio subcarrier to the UHF band or higher band, and , is provided with a filter circuit having a passband characteristic that significantly attenuates the harmonics of the subcarrier, which is the carrier wave of the audio subcarrier, so that the harmonics of the subcarrier and the video carrier frequency of the television signal to be transmitted ( It is possible to significantly reduce the audio spurious components caused by the main carrier frequency), and since the input signal frequency is relatively low, the above filter circuit can be easily configured. This transmitter for transmitting a television signal has the advantage of being able to transmit a television signal with almost no interference caused by spurious audio components to adjacent channels of a television receiver.

[Brief explanation of the drawing]

Fig. 1 is a block system diagram showing an example of a conventional television signal transmitter, Fig. 2 is a diagram showing an example of the frequency spectrum of the carrier wave in the output signal of the main part of Fig. 1, and Fig. 3 is a diagram showing an example of the frequency spectrum of the carrier wave in the output signal of the main part of Fig. 1. FIG. 4 is a diagram showing an example of the frequency spectrum of a carrier wave included in the output signal of the main part of the television signal transmitter according to the present invention. , 5 and 6 are block diagrams showing second and third embodiments of the television signal transmitter according to the present invention, respectively. 1... Audio signal input terminal, 2... Video signal input terminal, 8... Main carrier wave oscillator, 10, 13, 1
6, 21...television signal output terminal, 11,
15...Band filter, 12...Audio subcarrier amplitude modulator, 14...Audio subcarrier frequency modulator,
17... Luminance signal input terminal, 18... Carrier color signal input terminal.

Claims (1)

[Scope of utility model registration request] The audio subcarrier obtained by modulating a subcarrier of a predetermined frequency with an audio signal and the video signal are frequency-converted to the UHF band or higher band using the main carrier, and a television signal is obtained by frequency division multiplexing the two. In a television signal transmitter that transmits, at least the audio subcarrier is transmitted to an input signal transmission line system of a circuit for converting the frequency of the audio subcarrier to a UHF band or higher band,
and a television signal transmitter comprising a filter circuit having a passband characteristic that significantly attenuates harmonics of the subcarrier.