JPH0670295A - Catv output device - Google Patents

Abstract

PURPOSE:To make an output level constant regardless of channels by automatically offsetting the difference of the levels between output channels even when it is generated by the frequency characteristics of a frequency converter, an amplifier and a filter circuit. CONSTITUTION:The output levels of the respective channels of the output of the filter circuit 5 are measured and the lowest level of the channel is defined as a reference value. Then, at the other channels, the difference of the level with the reference value is calculated and stored in a memory 10 as a correction value. Then, at the time of controlling a variable attenuator 8, a CPU 9 reads the correction value corresponding to the output channel from the memory 10, turns it to a fixed value, supplies it to the attenuator 8 and controls attenuation amount. Thus, the difference of the levels between the output channels is offset and the output level at an output terminal 7 is fixed at all times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV output device in a CATV transmitting station.

[0002]

2. Description of the Related Art CA provided in a conventional CATV transmitting station
The TV output device is configured as shown in FIG. 1 is an input terminal of a video signal, 2 is an AM modulator, 3 is a frequency converter for converting into a predetermined carrier frequency, 4 is an amplifier, 5 is a filter circuit, and 6 is an output for setting an output level to an arbitrary value. The level adjusting circuit 7 is an output terminal. CA with this configuration
VHF (channels 1-12, video carrier frequency 91.25-103.
25 MHz, 171.25 to 217.25 MHz), mid band (channels C13 to C22, video carrier frequency 109.25 to 165.25 MHz), super high band (channels C23 to C63, video carrier frequency 223.225 to 463.25 MHz) ) Is possible.

[0003]

However, since the frequency converter, the amplifier and the filter circuit have frequency characteristics, even if the same amplifier gain and the same attenuation amount are applied, the output level varies depending on the selected output channel. For this reason,
The output level had to be adjusted for each output channel so that the output level was constant between channels.

[0004]

SUMMARY OF THE INVENTION The present invention provides a video signal A
An AM modulator for M modulation, a frequency converter for converting the output of the AM modulator into a predetermined carrier frequency, an amplifier for amplifying the output of the frequency converter, and a filter circuit for limiting the band of the amplifier output. In the CATV output device, variable level means for varying the output level of the filter circuit, control means for controlling the variable amount of the variable level means, and a correction value for correcting the variable amount according to the output channel are stored in advance. CAT with a memory
It is a V output device.

[0005]

By the above means, even if there is a level difference in the output of the filter circuit depending on the output channel, the variable amount of the variable level means is adjusted according to the output channel by the correction value from the memory, so the output level at the output terminal is the channel. It acts so as not to change by.

[0006]

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

FIG. 1 is a block diagram of a CATV output device according to the present embodiment. The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted. The feature of this embodiment is that a variable attenuator 8 is provided at the output stage, a CPU 9 that controls the attenuation amount of the variable attenuator 8 and a memory 10 that stores the attenuation amount controlled by the CPU as a correction value that differs for each output channel. Is the point that is arranged.

Next, a method of setting the correction value will be described. First, the output level of each channel at the output of the filter circuit 5 is measured and the output level of the lowest channel is used as the reference value. In other channels, the level difference from this reference value is calculated, and this is used as a correction value in the memory 10
To remember.

When controlling the variable attenuator 8, C
The PU 9 reads the correction value corresponding to the output channel from the memory 10, adds the correction value to a constant value, and supplies this to the variable attenuator 8 as control data to control the amount of attenuation.

As a result, the level difference between the output channels is canceled and the output level at the output terminal 7 is always constant.

Although the variable attenuator is used as the variable level means in this embodiment, a variable amplifier may be used instead.

[0012]

As described above, according to the present invention, even if a level difference between output channels occurs due to the frequency characteristics of the frequency converter, the amplifier, and the filter circuit, the variable level means at the final stage automatically cancels them out. Therefore, the output level can be made constant regardless of the channel.

[Brief description of drawings]

FIG. 1 is a block diagram of a CATV output device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional CATV output device.

[Explanation of symbols]

 2 AM modulator 3 Frequency converter 4 Amplifier 5 Filter circuit 8 Variable attenuator 9 CPU 10 Memory

Claims (1)

[Claims] 1. An AM modulator for AM-modulating a video signal,
A CATV output device comprising: a frequency converter that converts the output of the AM modulator into a predetermined carrier frequency; an amplifier that amplifies the output of the frequency converter; and a filter circuit that limits the band of the output of the amplifier. A CATV including variable level means for varying the output level, control means for controlling the variable amount of the variable level means, and a memory in which a correction value for correcting the variable amount according to the output channel is stored in advance. Output device.