JPS5915555B2 - TV signal audio carrier level adjustment device - Google Patents

Description

[Detailed Description of the Invention] This invention is a system for transmitting adjacent channels.In a television signal line of a common television reception facility, etc., the audio carrier wave of an adjacent channel is attenuated by a necessary amount to eliminate interference caused by the audio carrier wave. This invention relates to a television signal audio carrier wave level adjustment device used for.

0 When the adjacent channel transmission method is adopted, the audio carrier wave of the lower channel of the receiving channel interferes with the video signal of the receiving channel, and a 1.5 MH2 bead disturbance occurs on the screen.

Various types of obstacle removal devices have been constructed to eliminate this problem, but the conventional ones have the drawback of being extremely complicated and expensive. Therefore, there is a device in which a trap circuit is M-coupled to a bandpass filter to create a simple configuration and eliminate the above drawback, but since such a device is M-coupled, the amount of attenuation must be changed by adjustment, etc. o, the attenuation bandwidth and its center frequency change, which affects other carrier waves and causes the problem that even necessary components are attenuated. That is, according to the technical standards of the Broadcast Law Enforcement Regulations, the audio carrier wave is required to be suppressed to a level within the range of -9 to -14 dB below the level of the video carrier wave.

However, in general, it is said that around -15 to -20 dB is desirable (TV Community Receiving Technology No. 77 edited by Japan Broadcasting Corporation).
(see page). Therefore, when using the above M-coupling (for example, Japanese Patent Application Laid-Open No. 47-37335, Utility Model Application No. 5130-4226)
When using the M bond disclosed in Publication No. 0),
Suppose that the audio is 6 dB higher than the video carrier, and this is -1
If it is desired to attenuate to 4 dB, it is possible to obtain the desired amount of attenuation by using the M coupling described above. However, M
Coupling is closely related to the frequency 95 number, and as the amount of attenuation increases, f in Figure 2. The width of the band in the width direction with the center at is greatly expanded. Especially in 11ch, upper l
In the case described above, the color subcarrier region is also reached and this is reduced by 3.5 dB.

As a result, there are problems that cause color loss and hue changes.
When the above-mentioned value approaches -20 dB, this phenomenon increases the gain and color reproduction becomes impossible, and there is a problem that the desired attenuation adjustment cannot be made in practice. Furthermore, when adopting M-coupling technology, the structure is easy to adjust by site staff, and it also has a structure that does not cause color loss or color tone changes even if only the audio is attenuated to -14 dB to 20 dB (frequency band width). It is extremely difficult to create a device with a specific configuration (such as one that does not expand in the direction or move in the width direction), and there are problems that have not been realized even today. was strongly desired. Therefore, it is an object of the present invention to solve the above-mentioned problems, and as desired by those skilled in the art. Operation structure”
Moreover, it is an object of the present invention to provide a television signal audio carrier wave level adjusting device which has a simple configuration and can adjust the amount of attenuation of an audio carrier wave without affecting other carrier waves. The drawings showing the embodiments of the present application will be described below. In FIG. 1, 1 is an input terminal of a television signal audio carrier wave level adjustment device, 2 is an output terminal, 3 is a coupling coil installed on the transmission line between the input and output terminals 1 and 2, and 4 is a coupling coil. variable resistor connected to the midpoint of coil 3, 5 is a coupling capacitor,
A first parallel resonant circuit 6, which will be described below, is provided so as to be coupled to the transmission line with high impedance. In the first parallel resonant circuit 6, 7 is a first capacitor, 8 is a first coil, and 9 is a loss resistance of the coil 8. The resonant frequency of this first parallel resonant circuit 6 is made to match the frequency of the audio carrier wave for the purpose of level adjustment. Further, one end of this first parallel resonant circuit 6 is connected to the ground side terminal of the input and output terminals 1 and 2. 11 indicates a second parallel resonant circuit, in which 12 is a second capacitor, 13 is a second coil,
It is inductively coupled to a coupling coil 3.

14 indicates the loss resistance of the coil 13.

The coil and capacitor of this second parallel resonant circuit 11 are made to have the same resonance frequency as those of the first parallel resonant circuit 6 by using those having the same value as the coil and capacitor of the first parallel resonant circuit 6. 15 is an input side circuit such as an amplifier or an antenna connected to input terminal 1, 16 is an internal resistance thereof (generally 75Ω), and 17 is a load (such as a common reception line or television receiver) connected to output terminal 2 ( generally 7
5Ω) respectively. In the above configuration, the two parallel resonant circuits 6 and 11 constitute a high-frequency bridge circuit, and the variable resistor 4 unbalances the bridge.
It operates to determine the amount of attenuation at the 11 resonant frequencies.

Next, the manner in which the apparatus having the above structure attenuates the level of the interfering audio carrier wave will be explained based on FIG. 2.

When a television signal as shown in B enters the input terminal 1 of the television signal audio carrier level adjustment device having the above configuration having the passband characteristic as shown in A, the video carrier Fv is , the color subcarrier Fs is not affected at all, and only the audio carrier FA for the purpose of level adjustment is attenuated. Therefore, from output terminal 2, C
A television signal with a lowered level of the audio carrier wave C as shown in is output. The amount by which the audio carrier wave FA is attenuated is adjusted by changing the variable resistor 4. When the resistance value of the variable resistor 4 is large (1), only the second parallel resonant circuit 11 is involved and the amount of attenuation becomes small; When the value is small (several Ω), the first and second parallel resonant circuits 6 and 11 are comprehensively involved, and the amount of attenuation becomes large.

This situation is also clear from FIG. 3, which shows an example of actually measured values. Also, the minimum attenuation amount α (also called the minimum notch attenuation amount)
and the maximum attenuation amount β (also called the maximum notch attenuation amount) is
In order to satisfy the technical standards of the Cable Television Broadcasting Enforcement Regulations (the audio carrier wave of the lower channel should be kept within the range of -9 to -14 dB of the level of the video carrier wave of that channel), for example, α is 3 dB and 1 β is about 20 dB. selected. Next, when the amount of attenuation is changed, the attenuation bandwidth is as shown in Fig. 4.
Even when the attenuation amount is increased by decreasing the resistance value of , it becomes very narrow, and its center frequency does not deviate from the frequency of the audio carrier wave FA, as shown in FIG. 2A.

As described above, in the present invention, since the attenuation level of the audio carrier wave can be adjusted by the variable resistor 4 with the above-described configuration, it is possible to adjust the attenuation level of the audio carrier wave by the variable resistor 4. However, it has the advantage of being able to satisfy each of these requirements and having an extremely wide range of applications.

Furthermore, even though the level of the audio carrier wave is attenuated in this way, and even though the audio carrier wave has a frequency very close to that of the color subcarrier according to the standard, since it has the above-mentioned configuration, it is necessary to increase the amount of attenuation. Even in the case of
It has the advantage of allowing the color subcarrier to pass through as is, maintaining good color image reception. Moreover, since the device of the present invention has the above-described configuration, when adjusting the amount of attenuation as described above, it is possible to adjust the attenuation amount without changing the frequency to be attenuated (resonant frequency), that is, while keeping it consistent with the target audio carrier wave. It has the advantage that it can be attenuated and its adjustment can be done very easily. Furthermore, although the present invention has many excellent features as described above, its configuration includes first and second parallel resonant circuits 6, 11, a coupling coil 3 and a capacitor 5, and a variable Since it is extremely simple, using only the resistor 4, it also has the economical advantage of being able to be provided at a very low cost.

[Brief explanation of drawings]

The drawings show an embodiment of the present application, and FIG. 1 is a circuit diagram (equivalent circuit diagram), FIG. 2 is a diagram for explaining operating characteristics, and FIG.
The figure is a graph showing an example of the relationship between the value of the variable resistor and the amount of attenuation, and FIG. 4 is a graph showing the relationship between the value of the variable resistor and the bandwidth. 6...First parallel resonant circuit, 11...Second parallel resonant circuit, 4...Variable resistor, 3...
... Coupling coil, 5... Coupling capacitor.

Claims (1)

[Claims] 1 A coupling coil is interposed in the transmission line, and a series circuit of a variable resistor, a coupling capacitor, and a first parallel resonant circuit is installed at the midpoint of the coupling coil to adjust the attenuation level of the audio carrier wave. one end of the series circuit is connected, and the other end of the series circuit is grounded, and the first parallel resonant circuit is constituted by a first coil and a first capacitor, and its resonant frequency is adjusted. and a second resonant circuit including a second coil and a second capacitor and having the same resonant frequency as the first resonant circuit; 2. A television signal audio carrier level adjustment device, wherein the two coils are inductively coupled to the coupling coil so that the two parallel resonant circuits constitute a high-frequency bridge circuit.