JPS6024627B2 - wired tv system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention receives television waves, performs level adjustment at the head end, frequency conversion from UHF band to VHF band, and independent broadcast mixing, etc., and sends them to each subscriber via a transmission path. Regarding the cable television system that transmits this.

In cable television (hereinafter referred to as CATV) systems used in difficult-to-view areas and large-scale housing complexes,
Although it is generally possible to transmit multiple channels, each subscriber's general television receiver has a limited number of channels to select from, and cannot receive television waves from more channels than are scheduled for the receiver.

Furthermore, when a CATV system is used in a high-power area, a leading ghost (hereinafter referred to as "direct pickup") occurs due to the TV signal sent from the system's transmission line and the TV fin wave that jumps directly into the TV receiver from the air. This was a big problem. Therefore, a home converter was developed, which allows you to select multiple channels using a general TV receiver, and also converts received TV radio waves into signals of vacant channels and inputs them to the TV receiver, so it can be used for direct pickup. It can also prevent double images. However, a home converter was attached to each subscriber's television receiver only to solve the direct pickup problem in areas with strong electric fields, or to receive multiple channels in areas with non-strong electric fields where direct pickup did not occur. So it becomes very expensive.

The present invention takes the above-mentioned problems into consideration and attempts to provide an inexpensive and high-performance CATV system by incorporating the home converter function as an element of the system in advance.

An embodiment of the cable television system according to the present invention will be described below with reference to the drawings.

First, to explain the configuration, in FIG. 1, 1 is an antenna for receiving TV radio waves, and 2 is an antenna for amplifying received TV radio waves and self-broadcast TV radio waves (hereinafter, these radio waves will be referred to as the first signal SI) to a predetermined level. 3 is a fixed frequency oscillator that constantly oscillates a signal (hereinafter referred to as second signal S2) of a constant frequency (selected as a frequency that does not cause interference with the first signal SI); 4 is a fixed frequency oscillator that sends the signal to the main line 9; 1st and 2nd
This is a sending unit that sends out signals SI and S2 to the main line 9. 5
A. 5B'ma is placed in the middle of the main line 9, and the main line cable
Broadband (e.g. 50-290
6A and 6B are tap-offs for extracting television signals, 7 is a channel remote control device, and 8 is a television receiver for each subscriber.

As shown in FIG. 2, the channel remote control device 7 includes a branching filter 11, a first mixer 12, an intermediate frequency filter 3, an intermediate frequency amplifier 14, a second mixer 15, an output amplifier 16, a buffer amplifier 17, and a variable frequency It includes an oscillator 18, a control section 19, and an intensity setting device 20.

This channel remote device 7 is installed in each subscriber's home, and in particular, the control unit 19 functions as a channel switch that remotely controls the television receiver 18 to select a channel, and a channel number is engraved on the scale plate. . The variable frequency oscillator 18 outputs a third signal S3 whose frequency is always higher than the frequency of the channel to be selected by the intermediate frequency fi. Further, the intensity setting device 20 makes the level of the second signal S2 constant on the terminal side. The intensity setting device 20 is an attenuator when the second signal S2 is strong;
If it is weak, an amplifier is sufficient.Next, CA with such a configuration
The operation of the TV system will be explained. The first signal SI received by the receiving antenna 1 is amplified to a predetermined level by the head end 2 and sent to the main line 9. This first signal SI has a wide frequency band including multiple channels (for example, 90 to 22
2MHz) signal. On the other hand, the fixed frequency oscillator 3 always oscillates a second signal S2 of a specific frequency, and these signals SI and S2 are inputted to the main line amplifiers 5A and 58 via the main line 9 via the sending unit 4, where they are It is amplified and transmission loss is compensated. These signals SI and S2 are branched out from the main line 9 to the subscriber's terminal side by tap-off, for example 6B, and inputted to the channel remote control device 7. The signals S1 and S2 input to the channel remote control device 7 are split by a splitter 11, and the first signal SI is split by a first mixer 12.
The second signal S2 is set to a predetermined output level by the intensity setting unit 20 and input to the second mixer 15.
On the other hand, the subscriber sets the channel selector of the television receiver 8 to a predetermined empty channel (for example, channel 2 in the Tokyo area) and operates the control unit 10 to select the channel.

The variable frequency oscillator 18 is remotely controlled by this channel selection, changes its oscillation frequency, and outputs a signal S3 of a frequency corresponding to the selected channel. This signal S3 is input to the first mixer 12 via the buffer amplifier 17, mixed with the signal SI, and the mixed signal is output. This output signal includes not only an intermediate frequency signal for the desired channel but also a difference frequency signal for other channels. intermediate frequency signal SI
only is output from the filter. The same applies when the control unit 19 selects another channel, and the intermediate frequency signal frequency for the other channel is output from the same machine filter 13 as in the above case. This intermediate frequency signal Si is amplified by an intermediate frequency amplifier 14, inputted to a second mixer 15, mixed with a signal S2 inputted from an intensity setting device 20, and converted to the frequency of an empty channel of the television receiver 8.

This converted constant frequency signal is amplified by the output amplifier 16 and input to the television receiver 8. In this way, when a desired channel is selected by the control unit 19, an intermediate frequency signal Si corresponding to this desired channel is obtained from the first signal SI received by the television radio wave receiving antenna 1, and furthermore, this intermediate frequency signal Si is converted into a signal with a center frequency corresponding to an empty channel set on the television receiver 8, so that it can be received by the television receiver 8.

Here, the operation will be described in detail based on the specific frequencies of each signal SI, S2, and S3.

. For example, the first signal SI is 1 for television broadcasting.
It is a signal in a frequency band from 9 MHz to 22 Mizukawa z corresponding to channels 12 to 12. The second signal S2 has a frequency of, for example, 148M. The frequency of the third signal S3 changes sequentially in the range from 142M to 1-leg cape Z in accordance with the channel specified by the control unit 19, and is set, for example, in the correspondence relationship shown in the following table for each channel. . The intermediate frequency filter 13 has a center frequency of 4
The pass frequency is set to allow only the intermediate frequency signal Si of the egg z to pass.

First, the first signal (frequency band 9 Sengawaz to 22 Xiaogoz) received by the TV radio wave receiving antenna 1 is SI.
The second signal S2 of about 148M outputted from the fixed frequency oscillator 3 passes through the sending section 4 and is sent to the main amplifiers 5A and 5B.
The first signal SI is supplied to the first mixer 12, and the second signal S2 is supplied to the intensity setting device 20.

Here, it is assumed that the subscriber has previously set the television receiver 8 to channel 2, which is an empty channel, and when channel 4 is selected by the control unit 19, for example, the variable frequency oscillator 18 is remotely controlled to Third signal S
This third signal S3 is supplied to the first mixer 12 via the buffer amplifier 17 and mixed with the first signal SI. Among the signals of the difference frequency components output from the first mixer 12, an intermediate frequency signal Si having a center frequency of 4 MHz is used.
only passes through the intermediate frequency filter 13, is amplified by the intermediate frequency amplifier 14, and is supplied to the second mixer 15. The second mixer 15 mixes the intermediate frequency signal Si and the second signal S2 from the intensity setting device 20, generates a television signal with a center frequency of 99M ratio, and sends it to each subscriber via the output amplifier 16. is supplied to the television receiver 8. Therefore, the four-channel television signal specified by the control unit 19 is converted into a television signal with a center frequency corresponding to the two channels of the television receiver 8, so that the television receiver 8 can receive the television signal. In addition, when the subscriber uses the 12
If the channel is selected, the variable frequency oscillator 18
The third signal S3 of the two-legged cape z is output from the first and second signals.
The second mixer 15 outputs a television signal with a center frequency of 9 mz that can be received on the two channels set in the television receiver 8 by the mixers 12 and 15, the intermediate frequency filter 13, and the like.

In this way, the variable frequency oscillator 18 generates the third signal S3 having the frequency corresponding to the channel selected by the control section 19, so that it can be received on two channels of the television receiver 8. Furthermore, as another embodiment, as shown by the dotted line in FIG. 2, instead of connecting the intensity setting device 20 and the second mixer 15, the output of the intensity setting device 20 can be connected to the first 1
2, and in place of the connection between the buffer amplifier 17 and the first mixer 12, the buffer amplifier 17
is connected to supply V to the second mixer 15, and the first mixer mixes the first signal SI and the second signal S of a constant frequency.
2, the first signal SI is converted into an intermediate frequency signal S'i whose frequency is reduced by the constant frequency, and this intermediate frequency signal S'i and the third signal S'i from the variable frequency oscillator 18 are mixed. The signal S3 may be mixed with the second mixer 15 and converted into a signal with a specific frequency that matches the free channel frequency.

However, in this case, the intermediate frequency signal S'i is the first signal SI
Similarly, since it has a wide frequency band spanning multiple channels, it is necessary to make the intermediate frequency filter 13 and amplifier 14 compatible with the wide frequency band. Here, the operation will be explained based on the specific frequencies of each signal SI, S2, and S3.

For example, the first signal SI is 90M to 108M corresponding to channels 1 to 3 for television broadcasting.
It is a signal in the frequency band up to MHz. second signal S2
is a signal with a frequency of 148 MHz. The intermediate frequency filter 13 is set to a passing frequency that allows only the intermediate frequency signal Si having a center frequency of 5 MHz to 43 MHz to pass therethrough. On the other hand, the frequency of the third signal S3 changes successively in accordance with the channels designated by the control unit 19, and is set, for example, in the correspondence relationship shown in the following table for each channel. for example,
When one channel is selected by the control section 19, a third signal S3 with a ratio of 234M is output from the variable frequency oscillator 18, and is supplied to the second mixer 15 via the buffer amplifier 17.

On the other hand, in the first mixer 12, the first signal SI and the second signal S2 of 14 Kōjiji z from the intensity setter 20 are mixed, and a signal with a difference frequency component is output. The intermediate frequency signal S'j of the law matrix z is supplied to the second mixer 15 via the intermediate frequency filter 13.

In the second mixer, the intermediate frequency signal S′i and the third signal S
3 and a difference frequency component signal is output and supplied to the television receiver 8 via the output amplifier 16. That is, since the center frequency is converted to a television signal with a center frequency of 17 M&, the television receiver 8 receives an empty channel 5.
You can receive it on the channel. Even if another channel is selected by the control unit 19 in this way, the TV receiver 8
It can be received on 5 channels. As is clear from the above description, according to the present invention, by simply adding a constant frequency oscillator on the head end side and a channel remote control device on the subscriber side, it is possible to replace the conventional TV receiver in an existing CATV system. Since the fixed frequency oscillator installed on the head end side can be used in common by each subscriber, double super one-way reception can be achieved by installing only one variable frequency oscillator on each subscriber side. This makes it possible to more reliably prevent interference and simplify the circuit configuration.

Furthermore, since the television signal is input to the television receiver using an empty channel, the direct pickup problem can be effectively solved. Furthermore, by appropriately setting the output frequency range of the variable frequency oscillator, any number of channels can be received. In addition, in a CATV system that has an automatic level control device that uses a pilot signal, by using the pilot signal instead of a fixed frequency oscillator signal, it is possible to reduce the cost without adding so many devices to the conventional CATV system. The present invention can be applied.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a CATV system according to the present invention, and FIG. 2 is a block diagram showing the configuration of a channel remote control device. In the figure, 2 is a head end, 3 is a fixed frequency oscillator, 9 is a transmission line, 1 is a branching filter, 12 is a first mixer, 1
5 is a second mixer, and 1 is a variable frequency oscillator. Figure 2 Figure 1

Claims (1)

[Claims] 1. In a cable television system that receives television broadcasts, adjusts the received radio waves at the head end, and transmits them to each subscriber's terminal side via a transmission line, the head end side:
A fixed frequency oscillator that emits a constant frequency, and a sending section that sends a first signal output from the head end and a second signal output from the fixed frequency oscillator to the transmission path, On the terminal side, there is a branching filter that separates the first and second signals sent from the transmission line, and a variable frequency divider that outputs a third signal of a desired frequency for tuning according to the subscriber's operation. An oscillator mixes one of the second signal split by the splitter or the third signal from the variable frequency oscillator with the first signal split by the splitter to generate an intermediate frequency signal. a first mixer for converting the signal into a signal, and a first mixer for mixing the other of the second or third signals with the intermediate frequency signal outputted by the first mixer and converting the signal to the frequency of an empty channel of the television receiver. A cable television system characterized by being equipped with two mixers.