JPH04127677A - High-frequency conversion type catv converter with channel switching sound proofing function - Google Patents

Abstract

PURPOSE:To prevent a switching sound to be generated when switching a channel by separately providing the video/acoustic oscillator of the same channel frequency as an output and changing over a switch, which changes over signals in the case of reception and channel switching, according to a channel switching signal. CONSTITUTION:When the channel of a CATV converter 4 in switched, a mute signal is outputted from a mute pulse generation circuit 3, and an electronic switch 2 is changed over to the side of a TV signal carrier generation circuit 1. When the channel is completely switched, the mute pulse 3 is eliminated, and the electronic switch 2 is returned to the converter side. Thus, by applying a fixed TV signal carrier waveform, a noise signal is prevented from being generated by sweeping of the output signal of the converter when switching the channel.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-frequency CATV converter that prevents switching noise generated when switching channels.

[Conventional technology]

Regarding high frequency conversion type (hereinafter referred to as RF type) CATV converter, the one according to the present invention is not found, but JP-A-59-131
As described in Japanese Patent No. 276, the conventional method is to generally apply audio mute to the output after audio detection.

The conventional method is to re-modulate the audio muted signal (baseband method) to prevent noise that occurs when switching channels.

[Problem to be solved by the invention]

In conventional RF CATV converters, when switching channels, the frequency of the output second channel (or first channel) sweeps, so depending on the channel spacing, quite unpleasant noise (channel switching sound) is generated. This is a matter of great concern to some people, and it has been desired to reduce it.

When you change the channel of the RFi CATV converter,
The output channel signal causes transient frequency fluctuations,
The audio intermediate frequency (SIF) of 4.5M is intermittent, causing FM distortion due to level fluctuations and generating noise.

[Means to solve the problem]

The present invention was made in order to solve this problem, and in a high frequency conversion type CATV converter, separate video and audio oscillators of the same channel frequency as the output are provided,
The switch that changes the signal when receiving and changing channels,
This is a high-frequency CATV converter with channel switching sound prevention, characterized in that switching is performed by a channel switching signal.

[Effect]

In such a CATV converter, when switching channels of the converter, the electronic switch 2 receives a signal from the mute pulse generating circuit 3 and switches to receive the TV signal wave 1. This allows the TV to receive a stable TV signal even during channel switching periods, reducing audio noise.

〔Example〕

In Figure 1, 4 is a conventional RF type CATV converter, and 1 is a 1 or 2 channel with the same frequency as the converter output of 4.
A TV signal carrier generation circuit, 2 an electronic switch for switching signals 1 and 4, and 3 a mute pulse generation circuit.

Now, when the channel of the CATV converter 4 is switched, the mute pulse generation circuit 3 outputs a mute signal and the electronic switch 2 is switched to the TV signal carrier generation circuit 1 side. When the channel switching is completed, the mute pulse 3 disappears and the electronic switch 2 is returned to the converter side. In this way, the generation of a noise signal due to the sweep of the converter output signal during channel switching is prevented by adding a fixed TV signal carrier waveform.

In FIG. 1, when the TV converter channels are switched, an electronic switch 2 receives a signal from a mute pulse generating circuit 3 and is switched to receive a TV signal wave 1. This allows the TV to receive a stable TV signal even during channel switching periods, reducing audio noise.

In Figure 2, the RF type converter is equipped with a VTR selector switch to make it convenient to record programs on a VTR. Since the output of this converter is the second channel, the carrier wave of the second channel TV signal 9 is mixed with the input signal, and the signal generated when switching channels generates a mute pulse, which causes the electronic switch 6.7.8 By setting as shown in the figure and inputting the second channel switching signal carrier wave 9 to the TV side when switching channels.

No channel switching noise occurs.

At this time, if the level of the second channel TV signal 9 is increased, it is likely to cause interference such as cross-modulation and intermodulation with the input signal, so it is important to set the level to be lower than the converter output. Further, in order to prevent mixing from returning to the input side, it is desirable to install a branch or an attenuator.

〔Effect of the invention〕

According to the present invention, in an RF type CATV converter, channel switching noise can be prevented and the characteristic of not processing the baseband waveform in the RF type transmission path can be utilized.

Furthermore, the number of parts is smaller than that of the baseband type CATV converter, and the cost can be reduced.

4,

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and the figure shows the circuit diagram of FIG. 1; TV signal carrier wave generation circuit; 2; electronic switch; 3; mute pulse generation circuit. 4; RF type CATV converter. Second

Claims (1)

[Claims] 1. Channel switching in a high-frequency CATV converter, characterized in that a video and audio oscillator with the same channel frequency as the output is provided separately, and a switch for switching signals at reception and channel switching is switched by a channel switching signal. High frequency CATV converter with sound prevention.