JPH0730880A - Catv converter - Google Patents

Abstract

PURPOSE:To extend a dynamic range by controlling a level of an RF signal and a level in an incoming direction depending on a level of a data communication carrier in an outgoing direction to be detected. CONSTITUTION:This converter is provided with a variable gain circuit 1 receiving an RF signal inputted to an input terminal 6 via a cable from a trunk line amplifier and a data communication carrier in an incoming direction from a distribution line 1. The variable gain circuit 11 controls a level of an RF signal received by a control variable coincident with a setting value with a level represented by a level detection signal from an outgoing data demodulation circuit 4 and a level of a data communication carrier in the incoming direction. The RF signal whose level is controlled is given to the distribution circuit 1 and the data communication carrier in the incoming direction whose level is controlled is sent to a trunk line amplifier via a cable from the input terminal 6. The distribution circuit 1 distributes the RF signal from the variable gain circuit 11 into a television signal and the data communication carrier in the outgoing direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV converter having a bidirectional communication function.

[0002]

2. Description of the Related Art Generally, a CATV converter transmits an RF signal input thereto to a television receiver (hereinafter referred to as TV
It is converted into an RF signal corresponding to a receivable channel and output. This channel is 1 channel, 2
It is set to any one of the channels or the 13 channels of UHF.

As the above-mentioned channel conversion method, a channel conversion method is performed by directly converting an input RF signal, and a baseband video signal and a baseband audio signal are detected from the input RF signal. However, there is a method of converting channels by converting each video signal and audio signal into an RF signal again.

The reception band of a television signal handled by the CATV converter is a wide band of 90 to 450 MHz, and many CATV converters are provided with a unidirectional or bidirectional data communication function used for controlling them. ing.

In data communication using this data communication function, an RF-modulated data carrier is transmitted via a cable. As the frequency of this data carrier, a band of 70 MHz to 450 MHz is used for downlink data communication, and 10 MHz for uplink data communication.
The z-50 MHz band is used.

Next, a main part of the conventional CATV converter for processing an RF signal will be described with reference to the drawings. FIG. 2 is a block diagram showing a main part of a conventional CATV converter that processes an RF signal.

The CATV converter includes a distribution circuit 1 as shown in FIG. The distribution circuit 1 distributes an RF signal input from a main amplifier (not shown) to an input end 6 via a cable (not shown) to a television signal and a downlink data communication carrier, and also to an uplink direction. The data communication carrier is output from the input end 6 to the main line amplifier via the cable.

The television signal distributed by the distribution circuit 1 is given to the channel selection circuit 2. The channel selection circuit 2 selects a designated channel from the television signal and outputs the selected channel frequency to the IF detection circuit 3.

The IF detection circuit 3 converts the channel frequency into a constant intermediate frequency irrelevant thereto. The input to the IF detection circuit 3 is controlled by automatic gain control for the tuning circuit 2.

The downlink data communication carrier distributed by the distribution circuit 1 is given to the downlink data demodulation circuit 4, and the downlink demodulation circuit 4 performs demodulation processing on the downlink data communication carrier.

The upstream data communication carrier to the distribution circuit 1 is output from the upstream data modulation circuit 5. The upstream data demodulation circuit 5 performs a modulation process on the upstream communication data.

The level of the RF signal input to the distribution circuit 1 varies depending on the distance from the main amplifier provided in the middle of the main cable to the distribution circuit 1 or the distance from tap-off to the distribution circuit 1. However, since the output level of the main line amplifier is set to a constant value, there is a loss having a predetermined fluctuation range between the main line amplifier and the distribution circuit 1.

On the other hand, the sending level of the upstream data communication carrier from the distribution circuit 1 is set to be constant. Therefore, the level of the upstream communication carrier when reaching from the distribution circuit 1 to the trunk amplifier is different for each CATV converter, and the dynamic range of the trunk amplifier for the upstream communication data carrier is narrowed.

[0014]

As described above, in the conventional CATV converter having the bidirectional communication function, the dynamic range of the trunk amplifier for the upstream communication data carrier is narrowed.

An object of the present invention is to provide a CATV converter capable of widening the dynamic range of the trunk line amplifier for upstream communication data carriers.

[0016]

According to the present invention, an RF signal input from a main amplifier via a cable is distributed to a television signal and a downlink data communication carrier, and the uplink data communication carrier is described above. A CATV converter provided with a distribution means for outputting toward the main line amplifier via a cable, the level detection means detecting a level of the downlink data communication carrier distributed by the distribution means, A variable that takes in an RF signal and the upstream data communication carrier, and controls the level of the RF signal and the upstream communication data carrier according to the level of the downstream data communication carrier detected by the detection means. And gain means.

[0017]

[Operation] In the CATV converter of the present invention, the level of the downlink data communication carrier distributed by the distributing means is detected, and the RF signal of the RF signal is detected according to the detected level of the downlink data communication carrier. The level and the level of the upstream data communication carrier are controlled.

For example, when the level of the downlink data communication carrier is lower than a set value, that is, when the distance from the distribution circuit to the main amplifier is long, the variable gain means increases the level of the RF signal. Because of the control, the transmission level of the upstream data communication carrier becomes high. On the other hand, when the level of the downlink data communication carrier is higher than the set value, that is, when the distance from the distribution circuit to the main amplifier is short, the variable gain means controls to lower the level of the RF signal. Therefore, the sending level of the upstream data communication carrier becomes low. Therefore, the dynamic range of the trunk amplifier for the upstream communication data carrier can be widened.

Further, since there is a fixed relationship between the level of the downlink data communication carrier and the level of the television signal, the downlink RF is maintained.
The level of the television signal and the level of the downlink data communication carrier are controlled by controlling the level of the signal, and the output level of the television signal from the distribution circuit and the downlink data communication carrier are controlled. The output level from the distribution circuit can be held at a predetermined value.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a main part of an embodiment of a CATV converter of the present invention.

As shown in FIG. 1, the CATV converter includes a main amplifier (not shown) to a cable (not shown).
A variable gain circuit 11 is provided for taking in the RF signal input to the input terminal 6 via the and the upstream data communication carrier from the distribution circuit 1. The variable gain circuit 11 controls the level of the RF signal and the level of the upstream data communication carrier that are input with a control amount that matches the level indicated by the level detection signal from the downstream data demodulation circuit 4 described later and the set value. To do. The level-controlled RF signal is applied to the distribution circuit 1, and the level-controlled upstream data communication carrier is sent from the input end 6 to the trunk amplifier via the cable.

The distribution circuit 1 is the RF from the variable gain circuit 11.
The signal is distributed to a television signal and a downstream data communication carrier, and an upstream data communication carrier from an upstream data modulation circuit 5, which will be described later, is taken in and output to the variable gain circuit 11.

The television signal distributed by the distribution circuit 1 is given to the channel selection circuit 2, the channel selection circuit 2 selects a designated channel from the television signal, and the selected channel frequency is detected by the IF detection circuit 3 Output to.

The IF detection circuit 3 converts the channel frequency into a constant intermediate frequency irrelevant thereto. The input to the IF detection circuit 3 is controlled by automatic gain control for the tuning circuit 2.

The downlink data communication carrier distributed by the distribution circuit 1 is given to the downlink data demodulation circuit 4, and the downlink demodulation circuit 4 performs demodulation processing on the downlink data communication carrier and the downlink data communication. A level detection signal indicating the input level of the carrier is output.

An upstream data communication carrier to the distribution circuit 1 is output from the upstream data modulation circuit 5, and the upstream data modulation circuit 5 performs a modulation process on the upstream communication data.

Next, the operation of the CATV converter will be described.

CATV from main line amplifier via cable
The RF signal transmitted to the converter is taken into the variable gain circuit 11 from the input terminal 6, and the variable gain circuit 11 controls the level of the RF signal input to this.

R whose level is controlled by the variable gain circuit 11
The F signal is given to the distribution circuit 1, and the distribution circuit 1 distributes the signal input thereto to the television signal and the downstream data communication carrier.

The television signal is given to the channel selection circuit 2, and the channel selection circuit 2 selects the frequency of the designated channel from the television signal. The selected channel frequency is given to the IF detection circuit 3, and the IF detection circuit 3 converts the channel frequency into an intermediate frequency.

The downlink data communication carrier is given to the downlink data demodulation circuit 4. The downlink data demodulation circuit demodulates the downlink data communication carrier and outputs a level detection signal indicating the input level of the downlink data communication carrier.

The level detection signal from the downlink data demodulation circuit 4 is given to the variable gain circuit 11. Variable gain circuit 11
Controls the level of the RF signal input with a control amount for matching the level indicated by the level detection signal from the downlink data demodulation circuit 4 with the set value.

When the input level of the downlink data communication carrier to the downlink data demodulation circuit 4 is lower than the set value, that is, when the distance from the input end 6 to the main amplifier is long,
Since the variable gain circuit 11 performs control to increase the level of the RF signal input to it, the level of the downlink data communication carrier increases and the level of the television signal increases, and the downlink data communication increases. The input level of the carrier to the downlink data demodulation circuit 4 and the input level of the television signal to the channel selection circuit 2 can be controlled to appropriate values.

When the input level of the downlink data communication carrier to the downlink data demodulation circuit 4 is lower than the set value, when the uplink data communication carrier is transmitted toward the cable, the variable gain circuit 11 Controls the level of the upstream data communication carrier with the same control amount as the control amount for the RF signal input thereto, the level of the upstream data communication carrier becomes high and the input terminal of the upstream data communication carrier becomes high. The output level to 6 is controlled to an appropriate value for the long distance from the input terminal 6 to the main amplifier.

On the other hand, when the input level of the downlink data communication carrier to the downlink data demodulation circuit 4 is higher than the set value, that is, when the distance from the input end 6 to the main line amplifier is short, the variable gain circuit 11 operates as follows. RF input to
Since the control for lowering the signal level is performed, the level of the downlink data communication carrier is lowered and the level of the television signal is lowered, and the input level of the downlink data communication carrier to the downlink data demodulation circuit 4 is reduced. Also, the input level of the television signal to the tuning circuit 2 can be controlled to an appropriate value.

When the input level of the downlink data communication carrier to the downlink data demodulation circuit 4 is higher than the set value, when the uplink data communication carrier is transmitted to the cable, the variable gain circuit 11 Controls the level of the upstream data communication carrier with the same control amount as the control amount for the RF signal input to it, the level of the upstream data communication carrier becomes low and the level of the upstream data communication carrier becomes low. The output level to the input end 6 is controlled to an appropriate value for a short distance from the input end 6 to the main line amplifier.

As described above, the dynamic range of the trunk amplifier for the upstream communication data carrier can be widened regardless of the length of the distance from the input terminal 6 to the trunk amplifier.

[0039]

As described above, the CAT of the present invention
According to the V converter, the dynamic range of the trunk amplifier for the upstream communication data carrier can be widened.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of an embodiment of a CATV converter of the present invention.

FIG. 2 is a block diagram showing a main part that performs processing on an RF signal of a conventional CATV converter.

[Explanation of symbols]

 1 distribution circuit (distribution means) 2 channel selection circuit 3 IF detection circuit 4 downlink data demodulation circuit 5 upstream data modulation circuit 6 input terminal 11 variable gain circuit (variable gain means)

Claims (1)

[Claims] 1. An RF signal input from a main line amplifier via a cable is distributed to a television signal and a downstream data communication carrier, and an upstream data communication carrier is sent to the main line amplifier via the cable. In a CATV converter provided with a distributing means for outputting toward, a level detecting means for detecting a level of the downlink data communication carrier distributed by the distributing means, the RF signal and the uplink data communication carrier And a variable gain means for controlling the level of the RF signal and the level of the communication data carrier in the up direction according to the level of the data communication carrier in the down direction detected by the detecting means. CAT
V converter.