JPS59148480A - Video transmitter - Google Patents

Abstract

PURPOSE:To eliminate the generation of picture stripe pattern due to beat disturbance by providing a frequency variable means to change the oscillating frequency at beat disturbance generation to an oscillating circuit so as to change the frequency of the oscillating circuit when the beat disturbance occurs. CONSTITUTION:A video transmitter 2 of a television interphone consists of the oscillating circuit 6 and a modulating circuit 7. The oscillating circuit 6 is provided with a frequency varying means to vary the oscillated frequency, and an oscillating frequency control terminal 8 to control the frequency is led out of the frequency vary means so as to vary the frequency by an external control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a video transmission device used in a monitoring cable television system such as a telephone intercom.

[Background technology]

Figure 1 shows a schematic configuration diagram of a conventional TV intercom.
Using the composite video signal from + as a modulation signal, the video transmission device (2) K, which constitutes a so-called RF modulator, transmits an AM-modulated high-frequency 'signal to the monitor pin (4) via a coaxial cable (3). . Upper mouth vertical shijji (4
) side is provided with 9 (5).
e. The high frequency signal is converted into a baseband signal by the controller (5) and the image is displayed by the upper vertical receiver (4).

By the way, when an electromagnetic wave from a radio station rides on the coaxial cable (3) K in this transmission system, that voltage will appear at the end of the coaxial cable (3). For example, electric field strength 100
If there is a transmission system with a lever of dBμV/m, the voltage at the end of the coaxial cable (3) will be about 50dBμV. If this interfering wave is within the video transmission band (carrier frequency ±4.5 MHz in the double-sideband system), the long cylinder wave numbers of the carrier wave and the interfering wave appear as beats in the detection output of the decoder (6). This beat generation is illustrated in FIG. 2. In the figure, fQ is the carrier frequency f
c+ Δf indicates the frequency of the interference wave, and the frequency Δf appears as one.

[Purpose of the invention]

Kihatsu EJJ was developed in view of the above points, and its purpose is to provide a video transmission device that can eliminate beat interference.

[Disclosure of the invention]

FIG. 5 shows a schematic configuration diagram of a TV intercom using the video transmission device @ (2) according to the present invention. ),! - consists of an oscillation circuit (6
1K 1-1 A frequency variable means is provided so that the oscillation frequency can be varied, and an oscillation frequency control terminal (8) for controlling this frequency variable means is led out so that the frequency can be varied by an external control signal. It has become. Fig. 4 shows a concrete circuit of the oscillation circuit (6), which uses a crystal oscillator (9), and by changing the capacitance of a variable capacitance diode (lO). A device that can change the oscillation frequency, such as a variable capacitance diode (
The capacitance of 10) can be changed by changing the voltage applied to the oscillation frequency control terminal (8)K.

The video signal from the television camera fl+ is input to the modulation circuit (7) K and becomes a modulation signal, which AM modulates the oscillation output from the excavation circuit (6). This AM-modulated high-frequency signal is transmitted via a coaxial cable (3) to a digital television (4).
) side, demodulated by the demodulator (5), and displayed as an image on the upper vertical TV (4), where the interference radio waves get on the transmission system (when they increase, /-J oscillation frequency A signal is sent from the control terminal (8) to change the frequency of the oscillation circuit (6), thereby eliminating the influence of interference waves on the image. The relationship between the wave level and the 14-wave number of the beat is shown, and the horizontal scanning frequency of the video signal fH = 15, 75
It can be seen from this figure that the detection level is low for even numbers equal to 1/2 of KHy, and high for odd numbers. It is shown that when the frequency of the 9th one is an even number multiple of 1/2 of the horizontal scanning frequency fH, the interference to the image is noticeable, and when it is an odd number multiple, it is less noticeable. In the case of amateur radio, etc., the radio station radio waves that cause interference waves are not constantly emitted, so it is possible to detect interference from radio waves as an image. Since the upper interference wave frequency is not necessarily constant, the image may or may not be affected by beat interference.

Only when beat disturbance is detected in the horizontal scanning direction, that is, when a pattern occurs, the oscillation frequency of the oscillation circuit (6) is changed to the horizontal scanning same wave number fH using the oscillation frequency control terminal (8). By setting the carrier wave frequency so that the difference between the interference wave number frequency and the carrier wave frequency becomes an odd number signal of fH/2 by changing it within ±fH/2, the influence of interference waves on the image is reduced. It can be done. Furthermore, the fourth
In the circuit shown in the figure, the maximum frequency change can be set sufficiently to set the maximum frequency change. By making the voltage applied to K variable, it is possible to easily remove beat interference while looking closely at the image of plane 4).

Of course, the frequency may be automatically varied by providing a detection means for detecting beats and applying a control voltage to the oscillation frequency control terminal (8) in accordance with the output of the detection means.

[Effect of oscillation 1] The present invention provides an oscillation circuit that generates a carrier wave and an input video signal J.
It is equipped with a modulation circuit that AM modulates the oscillation output of the excavation circuit using i+ as a modulation signal, and transmits the AM modulated signal to the Nita TV side via a coaxial cable. Since the oscillation circuit is provided with a frequency variable means for changing the frequency, when beat disturbance occurs, the same wave number of the oscillation circuit is changed, and the generation of striped patterns in the image due to heat disturbance can be eliminated. .

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a conventional example, Figure 2 is a diagram 1 of an explanation based on the same interference wave generation state as above, (Figure 133 is a schematic configuration diagram of an embodiment of the present invention, and Figure 4 is a diagram of the same example). The circuit diagram of the oscillator circuit used,
Figure 5 shows the same wave number of P(・, the detection level of interference waves,
An explanatory diagram showing the relationship with the horizontal scanning frequency, Figure 0 is a circuit diagram of an oscillation circuit of another embodiment of the unreleased J, (3) is a coaxial cable, (4) is a monitor pin, (6) is an oscillation circuit, [7] is an LD modulation circuit, (8) is an oscillation frequency control terminal, (10) is a variable capacitance diode, and a VR/I transformer. Agent: Patent Attorney Ishi 1) Ishi seven

Claims (1)

[Claims] +1) An oscillation circuit that generates a carrier wave and a modulation circuit that uses an input video signal as a modulation signal to perform AM modulation on the oscillation output of the oscillation circuit, and transmits the AM modulated signal via a coaxial cable. What is claimed is: 1. A video transmission device for transmitting a video signal to a monitor television, characterized in that the oscillation circuit is provided with frequency variable means for changing the oscillation frequency when beat interference occurs. (2) A patent claim characterized in that the oscillation circuit is provided with frequency variable means for setting the difference between the same oscillation wave number and the interference wave frequency to approximately an odd multiple of 1/2 of the horizontal scanning frequency of the video signal. The video transmission device according to scope 1. (3) The video transmission device according to claim 1 or 2, which uses frequency variable means for changing the reversely applied voltage of the variable capacitance diode using a variable resistor.