JP2872000B2 - Television transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television transmitting apparatus, and more particularly to a television transmitting apparatus for protecting a transmitting circuit from the influence of noise contained in a video signal.

[0002]

2. Description of the Related Art In general, a video signal inputted to a television transmitting apparatus is mainly removed from a synchronizing signal and replaced with another synchronizing signal generated inside the television transmitting apparatus. The video signal of the television is used by amplitude-modulating the video signal, and the synchronization signal period has the maximum power value. The time ratio that the synchronization signal allows during the horizontal period is about 8%, and the average power during the horizontal period is 60% at most lower than the power value at the time of the synchronization signal.

However, when a video signal on which noise is superimposed on a transmission line upstream of a television transmission device is input to the transmission device, not only the synchronization separation circuit in the transmission device separates the synchronization signal, but also the noise signal is converted to the synchronization signal. In some cases. Therefore, these separated signals are replaced with a synchronization signal of the input video signal as a synchronization signal.

[0004] Therefore, when the time ratio of the synchronization signal during the horizontal period increases more than about 8%, the average power becomes sufficiently larger than the normal value.

[0005]

Conventionally, when noise is superimposed, especially in a device using a klystron for amplifying the video power of a transmission device, the body current rapidly increases in a short time and becomes an overcurrent. As a result, the protection circuit of the video power amplifying circuit operates to interrupt the transmission. For this reason, there was a drawback that continuous transmission was not possible.

SUMMARY OF THE INVENTION It is an object of the present invention to detect a video signal on which noise is superimposed, when the video signal is input to a transmission device, immediately detect the video signal, and suppress transmission power only during that period to prevent an increase in overcurrent and continue. It is an object of the present invention to provide a television transmission device capable of performing a specific transmission.

[0007]

In the present invention, a synchronizing signal and noise are used as a trigger signal in order to detect superposition of noise , from which two independent single-pulses having a constant width are formed. Immediate noise is detected by adding and comparing with a reference voltage, and a modulated output signal obtained by modulating a video signal is attenuated according to the detected signal, and continuous transmission can be performed by power-amplifying the attenuated output. A television transmission device is obtained.

[0008]

According to the present invention, even when a video signal on which noise is superimposed is input to a transmitting apparatus, continuous transmission can be performed by reducing the transmission power only during that period.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 is a diagram of one embodiment of the present invention. 2 and 3 are waveform diagrams for explaining the operation of the present invention. FIG. 2 shows a case where there is no noise, and FIG. 3 shows a case where noise is superimposed.

In FIG. 1, reference numeral 1 denotes a video signal input terminal, and a signal input from this terminal is transmitted to a video signal processing circuit 2. In the video signal processing circuit 2, the video signal is separated only by the sync signal in the sync signal separating circuit. The separated synchronizing signal is input to a half frequency dividing circuit 4 and its output is input to a single pulse generating circuit 5. After being transmitted to the circuit 6 for inverting the output of the half frequency dividing circuit 4, the signal is transmitted to another one-shot pulse generating circuit 7. The outputs of the single pulse generation circuits 5 and 7 are applied to an adder 8.

The output pulse width of the single-pulse generation circuits 5 and 7 is set to the synchronization signal cycle (63.5 μm in the NTSC system).
When no noise is superimposed by setting the time to about 20 microseconds shorter than (second), the outputs of the two single-pulse generation circuits 5 and 7 do not overlap in time as shown in FIG. On the other hand, when the noise is superimposed, as shown in FIG. 3, the synchronization signal separating circuit 3 separates not only the synchronization signal but also the noise signal as the synchronization signal, so that the time ratio occupied by the synchronization signal increases. Therefore, two single-pulse generation circuits 5,
7 may be overlapped in time. In this case, the adder 8 outputs twice the normal voltage.

The output of the adder 8 is compared with a predetermined reference voltage by a voltage comparator 9 so that when the output voltage of the adder 8 becomes twice the normal voltage, a signal from a modulation circuit 10 for modulating a video signal is output. It controls an attenuation circuit 11 that attenuates a high-frequency signal that is a modulation output. The output of the attenuation circuit 11 is sent to the power amplification circuit 12 to obtain a transmission output.

[0014]

As described above, according to the present invention, when a video signal on which noise is superimposed is input to a transmitting device, it is detected immediately and the transmission power is reduced only during that period, thereby reducing overcurrent. An increase can be prevented and continuous transmission can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a waveform diagram showing the operation of the embodiment of the present invention, showing a case where noise is not superimposed.

FIG. 3 is a waveform chart showing the operation of the embodiment of the present invention, showing a case where noise is superimposed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Video signal input terminal 2 Video signal processing circuit 3 Synchronous signal separation circuit 4 1/2 frequency dividing circuit 5 Single pulse generation circuit 6 Inversion circuit 7 Single pulse generation circuit 8 Adder 9 Voltage comparison circuit 10 Modulator 11 Attenuation circuit 12 Power amplifier circuit

Claims (2)

(57) [Claims] 1. A separation circuit for separating a pulse signal included in a video signal, and a first pulse generation for generating a first pulse having a predetermined pulse width shorter than a synchronization signal period based on the separated pulse signal. Circuit and the separated pulse signal
A second pulse generation circuit that generates a second pulse having a predetermined pulse width shorter than the synchronization signal cycle, an addition circuit that adds the first and second pulses, and an output of the addition circuit that is a reference voltage. A comparison circuit for comparing voltages, an attenuation circuit for attenuating a modulated output signal obtained by modulating a video signal in accordance with an output signal from the comparison circuit, and a power amplification circuit for amplifying the modulated output signal from the attenuation circuit and outputting a transmission output And the
The pulse widths of the first and second pulses are separated by the separation circuit.
The pulse signals to be applied are
A television transmitting apparatus, which is set so as not to be transmitted. 2. A frequency dividing circuit for dividing the separated synchronizing signal by １, and an inverting circuit for inverting an output of the frequency dividing circuit, wherein an output of the frequency dividing circuit is generated by the first pulse generator. To the circuit,
Television transmission system according to claim 1, wherein the supplying the output of the inverting circuit to said second pulse generating circuit.