JPH07147653A - High frequency unit - Google Patents

Abstract

PURPOSE:To improve the disturbance resistance to the signals of bands other than a TV broadcast band without increasing the cost by shifting plural filter trap circuits to the stage preceding a booster from the stage preceding a tuner. CONSTITUTION:The undesired signals of bands other than a TV broadcast band are eliminated in a high frequency unit 22 by an HPF 5 and a trap circuit 6 among those signals received through an ANT 1. Then the signals are amplified by a booster 2 and distributed to a TV output terminal 18 and the tuner part of a VTR by a distributor 3. At the tuner part, a desired CH is selected by a high frequency tuning circuit 7 and the signals are amplified by a high frequency amplifier circuit 8. Then the signals are mixed with the local oscillation signals 10 by a mixer 9 and outputted to a detection circuit through a terminal 11 as the IF output. Therefore the undesired signals are eliminated before they are amplified by the booster 2. Thus only the TV signals are supplied to the booster 2 and therefore no disturbance is caused at least by the signals of bands other than the TV broadcast band. The same effect is also secured with the terminal 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency unit used in video tape recorders, television receivers and the like.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, an RF modulator 12 having a booster (hereinafter abbreviated as an RF modulator) and a tuner 13 are housed in separate shield cases, and a coaxial cable 4 is provided between them. Was connected with. A signal input from the ANT (antenna) 1 is first amplified by the booster 2 and distributed by the distributor 3 to the TV output terminal 18 and the tuner output terminal 19 of the VTR 13. The signal input from the ANT input terminal 20 of the tuner 13 is first at a frequency lower than the HPF5 or the TV broadcasting band that allows the frequency components higher than the TV broadcasting band to pass, especially on the TV
A high frequency tuning circuit 7, through a trap circuit 6 that removes an IF frequency and a CB radio frequency that are likely to adversely affect reception.
It is sent to the high frequency amplifier circuit 8. After that, it is mixed with the local oscillation signal 10 by the mixer 9 and IF is output from the terminal 11 as IF output.
It is sent to a detection circuit (not shown).

In addition, an RF unit having a structure in which an RF modulator and a tuner are housed in one shield case 11 as shown in FIG. 3 has been developed because of the necessity of downsizing and cost reduction. At present, what has been put into practical use is a configuration in which an RF modulator and a tuner, which have been conventionally independent, are simply housed in one shield case and electrically connected, and the signal path configuration is that described in FIG. Is exactly the same as Therefore, the HPF and the trap circuit are provided in the subsequent stage of the booster.

[0004]

By the way, the booster of the RF modulator is designed to have a very flat characteristic so as to uniformly amplify the TV broadcasting band from 45 MHZ to 900 MHZ. Since it is designed to have a very wide band characteristic as described above, its ability to exclude signals outside the TV broadcasting band is inferior to that of a tuner. On the other hand, since the tuner selects and amplifies only the desired CH, it has an excellent interference elimination capability. Furthermore, the tuner is apt to interfere with the reception of TV with signals other than the TV broadcasting band, such as IF band and C
A trap circuit for strongly attenuating a signal in the B radio band is provided in the input portion.

In the circuit configuration of the conventional RF modulator and tuner, the signal coming from the ANT is amplified by the booster and then passes through the HPF / trap circuit in the preceding stage of the tuner, so that the booster also amplifies unnecessary signals other than the TV signal. Will end up. Also, when the electric field strength of the unnecessary signal is large, distortion is generated in the booster and the harmonics of the unnecessary signal are T
It may enter the V broadcast band and cause interference with the TV reception screen.

[0006] Recently, in Europe, there is a movement to tighten restrictions on interference resistance when an unnecessary signal is input. In particular, as for the interference resistance in the CB radio band, in the RF modulator having the conventional circuit configuration, since there is no filter or trap circuit in the preceding stage of the booster, the signal in the CB radio band is amplified as it is, and harmonics are also generated. Is very difficult to satisfy.

Therefore, the object of the present invention is to solve such a problem.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an RF modulator having a booster and a high-frequency unit of integral structure in which a television tuner is housed in one case.
The configuration is characterized in that a plurality of filter / trap circuits in the front stage of the tuner are arranged in the front stage of the booster.

[0009]

In the RF unit in which the RF modulator and the tuner are contained in one shield case, by moving the filter and the trap circuit originally arranged in the front stage of the tuner to the front stage of the booster of the RF modulator which is the signal inlet, Interference resistance to signals outside the TV broadcast band can be made very strong.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows a block diagram of a high-frequency unit embodying the present invention. The same parts as those in FIGS. 2 and 3 are designated by the same reference numerals and the description thereof will be omitted.

In the high frequency unit 22 of FIG.
The signal input from T1 is sent to the HPF5 and the trap circuit 6 for T
Unwanted signals other than the V broadcast band are first removed. Then, the booster 2 amplifies the signal, and the distributor 3 TVs.
It is distributed to the output terminal 18 and the tuner portion of the VTR.
Here, the tuner part indicates the high frequency tuning circuit 7, the high frequency amplifier circuit 8, the mixer 9, the local oscillation circuit 10, and the IF output terminal 11 of the high frequency unit 22.

In the tuner portion, the desired CH is selected by the high frequency tuning circuit 7, and the high frequency amplifier circuit 8 amplifies the signal. Then, the mixer 9 mixes it with the local oscillation signal 10 and outputs it as an IF output from the terminal 11 to the detection circuit.

With such a circuit configuration, since the unnecessary signal is removed before the signal is amplified by the booster 2, only the TV signal is input to the booster 2 and at least the TV signal is input.
Interference due to signals outside the broadcast band is eliminated. The same effect can be obtained with the TV output 16. In addition, with regard to jamming resistance, which is stricter in Europe, it is possible to satisfy the regulation without increasing the cost by implementing the present invention.

[0015]

In the prior art, since the booster was used to amplify the signal before passing it through the filter or trap circuit, it was vulnerable to interference signals outside the TV broadcast band. However, in the present invention, by utilizing the characteristic that the RF modulator and the tuner are housed in the same shield case, the total cost can be increased by moving the filter, which was conventionally arranged in the preceding stage of the tuner, to the preceding stage of the booster section. Instead, the characteristics of the booster part can be improved, and the interference exclusion regulations in Europe can be strengthened.

[Brief description of drawings]

FIG. 1 is a block diagram of a high-frequency unit embodying the present invention.

FIG. 2 is a diagram showing a combination of a conventional RF modulator and a tuner.

FIG. 3 is a diagram showing an integrated RF unit having the same circuit configuration as a conventional one.

[Explanation of symbols]

 1 ANT Input Terminal 2 Booster 3 Distributor 5 HPF 6 Trap Circuit 7 High Frequency Tuning Circuit 8 High Frequency Amplifier Circuit 9 Mixer 10 Local Oscillation Circuit 11 High Frequency Unit 15 Video Input Terminal 16 Audio Input Terminal 17 Mixer 18 TV Output Terminal

Claims (1)

[Claims] 1. An RF modulator having a booster and a high-frequency unit having a structure in which a television tuner is housed in one case, wherein a plurality of filter / trap circuits in the preceding stage of the tuner are arranged in the preceding stage of the booster. A high-frequency unit characterized by that.