JPH08307298A - Tv signal processor for catv system - Google Patents

Abstract

PURPOSE: To provide a simple and inexpensive processor by providing a channel selection section to a 2nd frequency conversion section converting an amplified intermediate frequency signal into a TV signal of a prescribed channel so as to change an output channel. CONSTITUTION: A band pass filter 10 passes a TV signal of a predetermined channel only among signals received by an input terminal 11. The selected TV signal is converted into an intermediate frequency signal by a 1st frequency conversion section 1 and amplified to a prescribed level by an intermediate frequency amplifier section 2. The TV signal amplified by the amplifier 2 is frequency-converted into a TV signal of a desired channel by a 2nd frequency conversion section 3. A channel selection section 4 is connected to a local oscillator 15 of the conversion section 3 and a voltage applied to two terminals 16, 17 is varied to vary the frequency. The signal outputted from the conversion section 3 is selected by a filter 18 and outputted to an output terminal 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TV signal processor used in a CATV system,
For example, it is installed at the receiving point of the CATV system.

[0002]

2. Description of the Related Art One of the amplifiers used at the receiving point of a CATV system is called a TV signal processor. This is because a received TV signal is converted into an intermediate frequency signal by a first frequency conversion unit (also called a down converter) A, this intermediate frequency signal is amplified by an intermediate frequency amplification unit B, and the amplified intermediate frequency signal is converted into a second frequency signal. A conversion unit (also called an up-converter) C is configured to convert into a TV signal of a predetermined channel determined in advance and output the TV signal. In this case, the conversion frequencies of both the first and second frequency converters A and C are fixed, and the output channel of the TV signal cannot be changed.

In addition to the above, there is a conventional one called a universal TV signal processor. This is because the received TV signal is converted into an intermediate frequency signal by the first frequency converter, and the intermediate frequency signal is amplified by the intermediate frequency amplifier.
The amplified intermediate frequency signal is converted to 450 by the second frequency converter.
It is converted into a signal with a frequency of MHz or higher, and then this signal is converted into a desired channel (70 to 45) by the third frequency converter.
(0 MHz) TV signal is converted and output. In this TV signal processor, the frequency conversion by the third frequency conversion unit is variable, and the output channel of the TV signal can be arbitrarily changed.

[0004]

In the CATV system, since the broadcast channel is rarely changed after the operation, the TV signal processor having the configuration shown in FIG. 2 usually causes no problem, but radio interference such as intermodulation occurs. Or
Even if I wanted to change the channel due to the change of facilities, I could not change the output channel. Therefore, if you still want to change the output channel,
I had to replace or modify the processor.

In preparation for such a case, 7 output channels are provided.
If you install a universal TV signal processor that can change the frequency band from 0 to 450MHz, you can easily change the output channel. However, since this processor uses the double conversion system, frequency conversion is easier than that of Fig. 2. One extra section is required, and an expensive amplifier circuit that suppresses the generation of harmonic distortion, intermodulation distortion, beat distortion, and the like must be used, which is complicated and expensive. . Therefore, this universal TV signal processor is used in special applications where output channels are frequently changed, but is rarely used otherwise.

It is an object of the present invention to provide a TV signal processor for a CATV system which can change the output channel and has a simple structure and is inexpensive.

[0007]

As shown in FIG. 1, a TV signal processor for a CATV system according to the present invention includes a first frequency converter 1 for converting an input TV signal into an intermediate frequency signal, and the intermediate frequency. The intermediate frequency amplifier 2 for amplifying the signal, and the amplified intermediate frequency signal for the TV of the predetermined channel.
CATV equipped with a second frequency converter 3 for converting into a signal
In the system TV signal processor, the frequency of the local oscillation signal of the second frequency conversion unit 3 is changed to the second frequency conversion unit 3 so that the amplified intermediate frequency signal has a frequency at which harmonic distortion occurs. The present invention is characterized in that a channel selection unit 4 is provided which is capable of converting only channels in the frequency range below the band.

[0008]

In the TV signal processor for CATV system of the present invention, the first frequency converter 1 for converting the input TV signal into the intermediate frequency signal, the intermediate frequency amplifier 2 for amplifying the intermediate frequency signal, and the amplifier In the TV signal processor for CATV system, which includes the second frequency conversion unit 3 for converting the intermediate frequency signal into a TV signal of a predetermined channel, the second frequency conversion unit 3 includes a station of the second frequency conversion unit 3. Since the frequency of the outgoing signal is varied and the amplified intermediate frequency signal can be converted only into the channels in the frequency range lower than the frequency band in which harmonic distortion occurs, the channel selection unit 4 is provided. Although it is a limited channel that does not cause wave distortion, TV
It is possible to change the output channel of the signal, and it is possible to avoid radio interference due to cross modulation or the like.

[0009]

First Embodiment One embodiment of a TV signal processor for a CATV system according to the present invention will be described in detail with reference to FIG. Reference numeral 10 shown in FIG. 1 is a band pass filter (BP) which can selectively pass only a TV signal of a predetermined channel from a signal input to an input terminal 11.
F).

1 shown in FIG. 1 is a band pass filter 1.
It is a first frequency conversion unit that frequency-converts the TV signal of the channel selected by 0 into an intermediate frequency signal. The first frequency conversion unit 1 includes a mixer 12 and a local oscillator 13, and mixes a TV signal input to the mixer 12 with a local oscillation signal oscillated by the local oscillator 13 to produce the same TV signal.
The signal is converted to an intermediate frequency signal.

Reference numeral 2 shown in FIG. 1 denotes an intermediate frequency amplifying section (IF section) for amplifying the intermediate frequency signal to a predetermined level. As this intermediate frequency amplification unit, a conventional amplification unit (a non-high performance type amplification unit that suppresses distortion as much as possible) is used.

Reference numeral 3 shown in FIG. 1 is a second frequency converter for frequency-converting the TV signal amplified by the intermediate frequency amplifier 2 into a TV signal of a desired channel. The second frequency converter 3 includes a mixer 14 and a local oscillator 15, and mixes the intermediate frequency signal input to the mixer 14 with the local oscillation signal oscillated by the local oscillator 15 to generate the intermediate frequency signal. It is for converting into a TV signal of a desired channel.

Reference numeral 4 shown in FIG. 1 is a channel selector.
The channel selector 4 is connected to the local oscillator 15 of the second frequency converter 3. This channel selector 4
Includes a VCO (Voltage Controlled Variable Frequency Oscillator), which varies the frequency of the output signal by varying the voltage marked on the two terminals 16 and 17, and
The frequency of the local oscillator signal is variable. In this case, the voltage applied to the terminals 16 and 17 is appropriately changed by a dip switch or the like (not shown). However, this channel selector 4 is the second
The range in which the output channel of the frequency converter 3 can be changed is
The output channels that are not affected by harmonic distortion are limited to within a few channels.

Reference numeral 18 shown in FIG. 1 is a band pass filter. The band pass filter 18 allows the TV signal output from the second frequency converter 3 to pass through only a few channels before and after the input channel as a reference. TV which passed this band pass filter 18
The signal is output to the output terminal 19.

[0015]

The TV signal processor for CATV system of the present invention has the following effects. 1. Since only a few output channels can be changed, an expensive amplifier is not required. 2. Since it is converted into a band in which harmonic distortion or the like does not occur, it is possible to easily avoid radio interference such as cross modulation. 3. Since double conversion is not required, the circuit structure is simple and the price is relatively low. 4. CAT that rarely changes the broadcast channel
It can be easily adopted even in the V system.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a TV signal processor for a CATV system according to the present invention.

FIG. 2 is a block diagram showing an example of a conventional TV signal processor for a CATV system.

[Explanation of symbols]

 1 1st frequency conversion part 2 Intermediate frequency amplification part 3 2nd frequency conversion part 4 Channel selection part

Claims (1)

[Claims] 1. A first frequency converter (1) for converting an input TV signal into an intermediate frequency signal, an intermediate frequency amplifier (2) for amplifying the intermediate frequency signal, and a predetermined intermediate frequency signal. A TV signal for a CATV system, including a second frequency conversion unit (3) for converting a channel TV signal.
In the processor, the second frequency conversion unit (3),
The frequency of the local oscillation signal of the second frequency conversion unit (3) is varied so that the amplified intermediate frequency signal can be converted only into a channel in a frequency range lower than a frequency band in which harmonic distortion occurs. A TV signal processor for a CATV system, comprising a channel selection unit (4).