JPH08163530A - Channel amplifier having provision for adjacent channel - Google Patents

Abstract

PURPOSE: To obtain the channel amplifier having provision for adjacent channels with ease of handling and excellent economy by providing a BPF on an input and an output side of a broad band amplifier section and providing a notch filter having a desired attenuation characteristic in a pre-stage of plural amplifiers in the broad band amplifier section. CONSTITUTION: A BPF 3 passing through only a TV signal is provided in an input side and an output side of a broad band amplifier section 2 in which plural RF amplifiers 1 are connected in series and a notch filter 4 with a steep characteristic to attenuate an audio carrier level of a TV signal is provided on the output side. When the filter 4 is removed and a notch filter 5 whose attenuation characteristic is not steeper than that of the filter 4 is provided on a pre-stage of each amplifier 1, a deviation in an attenuation point with respect to a temperature change and shock or the like is more gentle. As a result, the channel amplifier having provision for adjacent channels with ease of handling and excellent economy is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adjacent type channel amplifier used when a TV signal is transmitted by using adjacent channels in a CATV system, and an audio carrier level is converted to a video carrier level by a notch filter. The present invention relates to a notch filter type adjoining type channel amplifier which is attenuated to prevent interference of adjacent channels.

[0002]

2. Description of the Related Art In a CATV system, when a TV signal is transmitted using adjacent channels as shown in FIG. 2, in order to prevent interference between the TV signals of the adjacent channels, an audio carrier level is set. Must be reduced by about -9 to -14 dB with respect to the video carrier level for transmission.

Therefore, conventionally, the sound carrier level is attenuated by the amplifier H installed at the receiving point G of the system so as to have such a level relationship. In the conventional amplifier H of this type, a method using a notch filter and a TV
There is a method (signal processor method) of adjusting a sound carrier level by separating a signal into an intermediate wave of video and sound. Of these, the notch filter type amplifier H had a configuration as shown in FIG.

This amplifier H is provided with a bandpass filter C capable of passing only a TV signal of one channel on the input / output side of a wideband amplifier section B composed of two or more RF amplifiers A connected in series. A notch filter D for attenuating the sound carrier level of the TV signal is provided on the output side of the wide band amplifier unit B. The attenuation characteristic of the notch filter D is very steep as shown in FIG. 4, and the audio carrier f _A and the image carrier f having frequencies close to each other are used.
Only _V and the voice carrier f _A can be attenuated by a desired level.

[0005]

However, the notch filter D having a steep attenuation characteristic as shown in FIG. 4 has problems that the adjustment is severe and that the attenuation point is very likely to shift due to temperature change or shock. It was very difficult to handle. For example, even if the attenuation point is slightly deviated, the voice carrier f _A cannot be attenuated to a desired level, which may cause interference. Although the above problem does not occur in a signal processor type amplifier that does not use a notch filter, an amplifier of the same type is expensive and a notch filter type amplifier that is easy to handle has been desired.

It is an object of the present invention to provide an adjacency type channel amplifier capable of solving the above problems.

[0007]

As shown in FIG. 1, an adjacency type channel amplifier according to the present invention is provided on the input / output side of a wide band amplifier section 2 in which two or more RF amplifiers 1 are connected in series.
A bandpass filter 3 that allows only one channel of a TV signal to pass therethrough is provided, and a notch filter 4 having a steep characteristic for attenuating the sound carrier level of the TV signal is provided on the output side of the wideband amplifier section 2. In the adjacent correspondence type channel amplifier, the notch filter 4 is removed, and the notch filter 5 having an attenuation characteristic that is not steeper than the characteristic of the notch filter 4 is arranged in front of each RF amplifier 1. It is a feature.

[0008]

In the adjacency type channel amplifier of the present invention, the notch filters 5 having a steep characteristic are arranged in front of the RF amplifier 1 constituting the wide band amplifier section 2, and the sound carrier level is gradually increased by each notch filter 5. , The voice carrier level can be lowered to a target level. Moreover, in this amplifier, the notch filter 5 having a steep characteristic is used in place of the notch filter 4 having a steep characteristic in the related art, so that the attenuation point is less likely to shift due to temperature change, shock, etc., and it is easy to handle.

[0009]

[Embodiment 1] FIG. 1 shows an embodiment of an adjacent channel amplifier according to the present invention. This amplifier is a channel-dedicated type amplifier in which a band-pass filter 3 that allows only one channel of a TV signal to pass through is provided on the input / output side of a wide band amplifier unit 2 composed of three RF amplifiers. Three Rs that compose the broadband amplifier unit 2
A notch filter 5 having a characteristic that is not steep is inserted in front of the F amplifier 1.

The RF amplifier 1 is of a wide band type and has been conventionally used for an adjacent type channel amplifier.

The band-pass filter 3 can pass only one channel TV signal, and for example, an amplifier for four channels can pass only four channel TV signals.

The notch filter 5 is an attenuator circuit capable of selectively attenuating only the audio carrier from the audio carrier and the video carrier having similar frequencies. Each notch filter 5 is basically an attenuator having an attenuation curve as shown in FIG. 4, but the attenuation characteristic of each notch filter 5 is not as steep as that of FIG. 4, and three notch filters are combined. For the first time, the same attenuation characteristic as in FIG. 4 is obtained comprehensively. The notch filter 5 has its attenuation frequency characteristic adjusted so that the sound carrier can be attenuated from the TV signal of the channel to be amplified.

[0013]

EFFECTS OF THE INVENTION In the adjacent channel amplifier according to the present invention, the notch filter 5 is used, but the deviation of the attenuation point with respect to temperature change, shock, etc. is gentle. Easy to. Moreover, since it is cheaper than a signal processor type amplifier, it is easy to introduce.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an adjacent type channel amplifier of the present invention.

FIG. 2 is a schematic diagram showing an example of a CATV system transmitting adjacent channels.

FIG. 3 is a block diagram showing an example of a conventional adjacent corresponding channel amplifier.

FIG. 4 is an explanatory diagram showing characteristics of a notch filter used in the amplifier of FIG.

[Explanation of symbols]

 1 RF amplifier 2 Wideband amplifier section 3 Bandpass filter 4 Notch filter 5 Notch filter

Claims (1)

[Claims] 1. A bandpass filter (3) which allows only one channel of a TV signal to pass through on the input / output side of a wideband amplifier section (2) in which two or more RF amplifiers (1) are connected in series. The adjacent notch filter, which is provided with a notch filter (4) having a steep characteristic for attenuating the sound carrier level of the TV signal, is provided at the output side of the wide band amplifier section (2). (4) is removed, and a notch filter (5) having an attenuation characteristic that is less steep than the characteristic of the notch filter (4) is arranged in front of each RF amplifier (1). Type channel amplifier.