JP2001339706A - Catv system, up converter and down converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a CATV system with low cost which can transmits satellite reception signals on low frequency with less transmission loss by using down/up converters. SOLUTION: In the CATV system which is equipped with a down converter 20 to convert the frequency from the satellite reception signal by BS antenna to the satellite transmitting signal in 400 MHz band on the head end, and an up converter 30 to convert the frequency from the satellite transmitting signal to the original satellite reception signal on a transmission line of each subscriber side, this system is equipped with a FM modulating circuit to generate FM waves as the reference signal for use in generating high frequency signals for frequency conversion in the down converter 20, thereby, this system is arranged to be able to generate high frequency signals for frequency conversion by using the common reference signal in each of the converters 20 and 30 through transmitting this standard signal to each terminal side. As the result, the satellite receiving signal can be restored correctly in the side of the up converter 30. The satellite transmitting signal can be set into a scramble condition to be unable to receive illegally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV system for transmitting a satellite reception signal from a satellite reception antenna to a terminal together with a terrestrial television broadcast signal, and to transmit a satellite reception signal to the terminal using the CATV system. Down converter and up converter that are suitable for

[0002]

2. Description of the Related Art Conventionally, a head-end is provided with a television receiving antenna for receiving a terrestrial television broadcast signal and a satellite receiving antenna for receiving a radio wave transmitted from an artificial satellite (broadcast satellite or communication satellite). There is known a CATV system configured to transmit a reception signal from a reception antenna to a terminal via a common transmission line (generally, a coaxial cable).

[0003] By the way, a receiving part of a satellite receiving antenna usually transmits a transmission wave in the tens of GHz band transmitted from an artificial satellite to about 1 GHz to 2 GHz so that a received signal can be transmitted using a coaxial cable or the like. Is provided with a converter for frequency conversion (down conversion),
The reception signal (satellite reception signal) from such a satellite reception antenna must be transmitted by an existing CATV system in which transmission equipment such as an amplifier installed on a transmission line is designed to transmit a terrestrial television broadcast signal. There was a problem that can not be.

Further, since a satellite reception signal has a higher frequency than a terrestrial television broadcast signal, even if a transmission device installed on the transmission line is capable of transmitting the satellite reception signal, the transmission line is used. There is also a problem that transmission loss caused by flowing through the antenna increases, and an expensive amplifier having high-level amplification characteristics is required to transmit a satellite reception signal at an appropriate level.

[0005] Therefore, in order to be able to transmit a satellite reception signal even with an existing CATV system designed to transmit a terrestrial television broadcast signal and to transmit the satellite reception signal with low loss, On the head end side, a down converter is provided to temporarily drop the satellite reception signal to the frequency band of the television broadcast signal, and the satellite reception signal (hereinafter referred to as a transmission satellite signal) frequency-converted by this down converter is transmitted to the terminal side. Transmission is considered.

Further, in the CATV system in which the down-converter is provided on the head end side to convert the frequency of the satellite reception signal from the satellite reception antenna into a transmission satellite signal having a lower frequency, , The satellite signal for transmission transmitted to the terminal side via the transmission line is directly input to the subscriber side terminal device (so-called BS tuner or CS tuner), and the terminal device demodulates the desired broadcast signal. Can not do it. For this reason, in this type of CATV system, an up-converter for converting the frequency of the transmission satellite signal into the original satellite reception signal (so-called up-conversion) is provided on the transmission line for guiding the transmission satellite signal to the subscriber terminal. There is a need.

By the way, the down converter and the up converter described above input a satellite reception signal or a transmission satellite signal to be subjected to frequency conversion and a high frequency signal for frequency conversion to a mixing circuit, thereby obtaining a satellite reception signal or a high frequency signal. The transmission satellite signal is converted into a desired frequency determined by a frequency difference (or a frequency sum) of input signals to the mixing circuit.

For this reason, the above-mentioned down converter and up converter usually include a local oscillator for generating a high frequency signal for frequency conversion, a reference oscillator for generating a reference signal of a constant frequency (a so-called reference clock), The reference signal from the oscillator and the high-frequency signal from the local oscillator are respectively divided (multiplied in some cases) and taken in, and the oscillation frequency of the local oscillator is controlled so that the phase difference becomes zero.
An LL circuit is incorporated, and by the operation of the PLL circuit, a high-frequency signal used for frequency conversion can always be controlled to a constant frequency.

[0009]

However, using such a conventional down / up converter, the CA
When a TV system is constructed, frequency conversion in each converter can be performed satisfactorily, but if the oscillation frequency of the reference oscillator incorporated in each converter deviates, the up-converter receives the transmission satellite signal from the original satellite. There is a problem that the frequency cannot be accurately converted to a signal.

In order to prevent this problem, a high-precision oscillator may be used as a reference oscillator provided in each converter to make the oscillation frequencies of the respective reference oscillators coincide with each other. There is a problem that the cost is increased. In this case, in particular, since the upconverter is provided for each subscriber,
The financial burden on the subscriber may increase, and the number of subscribers to the CATV system may decrease.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and realizes a low cost CATV system capable of transmitting a satellite reception signal at a low frequency with a small transmission loss by using a down converter and an up converter. The purpose is to be able to.

[0012]

Means for Solving the Problems and Effects of the Invention A CATV according to claim 1 has been made to achieve the above object.
In the system, on the head end side, the satellite reception signal from the satellite reception antenna is overlapped with the television broadcast signal flowing in the transmission line in the frequency domain from VHF band to UHF band allocated for the television broadcast signal. There is provided a down converter for converting the frequency of the transmission satellite signal into a predetermined frequency band which does not perform transmission, and an up converter for converting the frequency of the transmission satellite signal to the original satellite reception signal is provided on the transmission line of each subscriber. Is provided.

In the down converter, a reference signal generating means for generating a reference signal of a predetermined frequency band which can be transmitted in a downstream direction from the head end to the subscriber terminal via a transmission line, and this reference signal is stored in the down converter. Reference signal transmitting means for transmitting the signal on the transmission line is provided, and the up-converter is provided with reference signal extracting means for extracting the reference signal transmitted from the head end side.

Therefore, according to the CATV system of the present invention, a satellite reception signal from a satellite reception antenna is frequency-converted into a transmission satellite signal of a lower frequency than that of the satellite reception signal, and the satellite reception signal is transmitted. Not only can transmission be performed with low loss, but also the down converter and the up converter can use the common reference signal generated by the reference signal generation means in the down converter to perform frequency conversion on the satellite reception signal and the transmission satellite signal, respectively. In other words, the upconverter can restore the original satellite reception signal from the transmission satellite signal with extremely high accuracy.

Further, since it is not necessary to provide a reference signal generating means in the upconverter, it is possible to provide an inexpensive upconverter provided for each subscriber, thereby reducing the financial burden on the subscriber and extending the cost. Can increase the number of subscribers to the CATV system.

Here, the reference signal generated by the reference signal generating means may be a carrier having a constant frequency, but more preferably a modulated signal obtained by frequency-modulating or phase-modulating the carrier as described in claim 2. It is good to And
In this way, the transmission satellite signal frequency-converted by the down converter will periodically shift in frequency or phase in conjunction with the reference signal, and those who do not have an up converter will be Even if an attempt is made to illegally receive a satellite broadcast by frequency-converting a transmission satellite signal into a satellite reception signal using the converter described above, the satellite broadcast cannot be received. In other words, according to the CATV system according to the second aspect, the satellite signal for transmission is in a state in which the so-called scramble is applied to the satellite reception signal, and a person who tries to watch the satellite broadcast illegally is not allowed to take an illegal action. Can be stopped.

In the CATV system according to the second aspect, the frequency or phase of the transmission satellite signal is periodically shifted by the reference signal, but the up converter uses the same reference signal as the down converter to transmit. The received satellite signal is frequency-converted to the original satellite received signal, so that the subscriber having a regular up-converter can receive the normally restored satellite received signal, and the subscriber can receive the signal via the up-converter. By inputting the received satellite signal to a terminal device such as a satellite tuner, satellite broadcasting can be viewed without any problem.

Further, as described above, the CATV according to claim 2
According to the system, the downconverter can be used as a scrambler, so that it is not necessary to use an expensive scrambler generally used in the past to prevent unauthorized reception of satellite broadcasts, thereby preventing unauthorized reception of satellite broadcasts. A possible CATV system can be realized at low cost.

On the other hand, the frequency of the reference signal generated by the reference signal generation means is set to a frequency that can be transmitted in the transmission line in the downward direction, and that does not overlap with a transmission satellite signal or another television broadcast signal. Although there is no problem, it is more preferable to set the frequency to the lower frequency side within the frequency band that can be transmitted in the down direction via the transmission line, as described in claim 3. That is, if the frequency of the reference signal is made as low as possible, the transmission loss when the reference signal flows down the transmission line can be reduced, and the signal level of the reference signal generated by the reference signal generating means can be reduced. Thus, power consumption of the down converter can be suppressed.

Since the downstream transmission band of the CATV system is generally 70 MHz or more, the frequency of the reference signal is preferably about 70 MHz. It is preferable to set the frequency slightly lower to about 69 MHz to 69.5 MHz.

Next, a down converter according to a fourth aspect is the CATV according to any one of the first to third aspects.
A reference signal generating means for realizing a system, a local oscillation means for generating a high frequency signal for frequency conversion, and an oscillation frequency control means for controlling the oscillation frequency of the local oscillation means based on the reference signal Mixing means for mixing the high frequency signal from the local oscillation means and the satellite reception signal to convert the satellite reception signal into a transmission satellite signal and transmitting the signal on a transmission line; and a reference signal generated by the reference signal generation means. On the transmission line.

Therefore, according to this down converter,
In addition to the transmission satellite signal after the frequency conversion, a reference signal used for frequency conversion of the satellite reception signal into the transmission satellite signal can be transmitted to the terminal via the transmission line. The CATV system of the first to third aspects can be constructed.

In the down converter according to the fifth aspect of the present invention, the reference signal generating means is constituted by using an FM modulation circuit for frequency-shifting a carrier having a constant frequency by a predetermined amount in a predetermined period. From the signal generation means, FM
The FM modulation signal generated by the modulation circuit is output as a reference signal. For this reason, this downconverter has a function as a scrambler for scrambling the satellite reception signal, and it is possible to construct the CATV system according to the second aspect.

On the other hand, the upconverter according to claim 6 is a CATV according to any one of claims 1 to 3 described above.
A reference signal extracting means for extracting a reference signal transmitted via a transmission line, and a transmission satellite signal transmitted via a transmission line into an original satellite reception signal. Local oscillation means for generating a high-frequency signal for frequency conversion, oscillation frequency control means for controlling the oscillation frequency of the local oscillation means based on a reference signal, and mixing of the high-frequency signal from the local oscillation means and the satellite signal for transmission Mixing means for frequency-converting the transmission satellite signal into the original satellite reception signal and transmitting the signal to the subscriber terminal.

Therefore, according to this upconverter,
By the operation of the oscillation frequency control means, the oscillation frequency of the local oscillation means can be made to coincide with the frequency of the high-frequency signal used by the down-converter to convert the frequency of the satellite reception signal into the transmission satellite signal. In other words, the original satellite reception signal can be accurately restored from the transmission satellite signal. Therefore, if this upconverter is used, the CATV system of the present invention (claims 1 to 3) can be constructed.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of the entire CATV system according to the embodiment. As shown in FIG. 1, the CATV of this embodiment
At the head end 2 of the system,
A well-known VHF antenna 12 and a UHF antenna 14 for receiving a television broadcast signal transmitted from a terrestrial broadcast station;
A known satellite receiving antenna (hereinafter referred to as a BS antenna) 18 which receives a transmission radio wave from a broadcasting satellite (hereinafter simply referred to as a BS), converts it into a 1 GHz band intermediate frequency signal (hereinafter referred to as a satellite received signal), and outputs it; Is provided.

The signals (television broadcast signals) received from the VHF antenna 12 and the UHF antenna 14 are amplified or frequency-converted by the signal processing circuit 16,
The signal is transmitted via a mixer (MIX) 22 onto a transmission line 6 composed of a coaxial cable or the like. In addition, the satellite reception signal from the BS antenna 18 is converted by the down converter 20 at a frequency different from that of the television broadcast signal output from the signal processing circuit 16, and from the VHF band assigned to the terrestrial television broadcast signal to the UHF band. After the frequency conversion to a predetermined frequency band up to the band (in this embodiment, a 400 MHz band between 222 MHz and 470 MHz which is not used for television broadcasting between the VHF band and the UHF band),
The data is transmitted onto the transmission line 6 via the mixer 22.

The mixer 22 combines the television broadcast signal output from the signal processing circuit 16 with the frequency-converted transmission satellite signal output from the downconverter 20 as it is, and sends out the signal onto the transmission line 6. belongs to. Next, the signal transmitted from the head end 2 onto the transmission line 6 via the mixer 22 is transmitted to the transmission line 6 and an amplifier or a branch amplifier (not shown) provided on the transmission line 6 or a branch amplifier shown in FIG. Is transmitted to a number of subscriber-side facilities subscribing to the CATV system via a security device 8, and further, a security device 10 and a subscriber-side transmission line 6 are connected to the subscriber-side terminal device 4.
Is entered via

Also, among the subscribers of the CATV system, those who want to view the BS broadcast are provided with the subscriber side terminal device 4 in addition to the BS tuner 26 and the television receiver 28 for receiving the BS broadcast. And down converter 2
An up-converter 30 is provided for frequency-converting the transmission satellite signal frequency-converted at 0 to the original satellite reception signal output by the BS antenna 18.

The transmission satellite signal transmitted to the subscriber terminal device 4 via the transmission line 6 is transmitted to the up-converter 3 provided on the transmission line to the BS tuner 26.
At 0, the frequency is converted to the original satellite reception signal, and the satellite reception signal after the frequency conversion is input to the BS tuner 26. As a result, the BS antenna 1 is
The same signal as the satellite reception signal output from 8 is input, the BS broadcast signal is demodulated by the BS tuner 26, and the video and audio can be reproduced by the television receiver 28.

FIG. 2 is a block diagram showing the configuration of the down converter 20 and the up converter 30.
As shown in FIG.
An oscillation circuit (hereinafter referred to as VCO) 42 capable of controlling the oscillation frequency by a voltage is provided as the local oscillation means described in (1). The output from the VCO 42 (1.4 in this embodiment)
GHz-band high-frequency signal) and a 1-GHz band satellite reception signal output from the BS antenna 18 (BS-I shown in the figure).
F) is mixed with a mixing circuit 44 comprising a well-known double-balanced mixer, for example, to convert the satellite reception signal into a 400 MHz band transmission satellite signal (BS-IF2 shown in the figure) in a so-called upper local area. Frequency conversion. The mixing circuit 44 corresponds to the mixing means according to the fourth aspect.

The down converter 20 has a VCO
A frequency dividing circuit 46 for dividing the output (high-frequency signal) from the frequency divider 42 at a predetermined frequency dividing ratio, and a constant frequency (69.5 M in this embodiment)
(Hz), a reference oscillation circuit 48 composed of a crystal oscillator or the like for generating a reference signal, a frequency dividing circuit 50 for dividing the reference signal generated by the reference oscillation circuit 48 at a predetermined frequency dividing ratio,
6 and 50, a phase comparator 52 for generating a signal corresponding to the phase difference, and a loop filter 54 for integrating the output from the phase comparator 52 to generate a control voltage for the VCO 42. And are provided.

The frequency divider circuits 46 and 50, the phase comparator 52, and the loop filter 54 increase the oscillation frequency of the VCO 42 to a frequency obtained by multiplying the frequency of the reference signal by a predetermined value determined by the frequency division ratio of each of the frequency divider circuits 46 and 50. This is for controlling, and constitutes a so-called PLL circuit. Accordingly, the oscillation frequency of the VCO 42 becomes a constant frequency obtained by multiplying the reference signal by a predetermined value, and the satellite reception signal output from the BS antenna 18 becomes
Frequency conversion is always performed using a high-frequency signal having a constant frequency.

In this embodiment, the reference oscillation circuit 48
Is equivalent to the reference signal generating means according to claim 4, and PL
Frequency divider circuits 46 and 50 constituting the L circuit, phase comparator 5
2 and the loop filter 54 function as the oscillation frequency control means. In the downconverter 20, a directional coupler 56 for transmitting a reference signal output from the reference oscillation circuit 48 to the terminal side is provided on the transmission line 6 closer to the terminal side than the mixing circuit 44. . Therefore, the reference signal is transmitted to the terminal together with the frequency-converted transmission satellite signal that has passed through the mixing circuit 44. In addition, this directional coupler 56 is described in claim 4.
Corresponds to the reference signal transmitting means described in (1).

Here, the signal passing through the mixing circuit 44 includes 400M which is a difference component between a high frequency signal (1.4 GHz band) from the VCO 42 and a satellite reception signal (1 GHz band).
Not only the transmission satellite signals in the Hz band but also the signals in the 1.8 GHz band, which are the sum components of these signals, are included.

However, since this signal is higher than the frequency that can be transmitted by the CATV system, the signal is greatly attenuated by passing through the transmission line 6 and various transmission devices provided on the transmission line 6, and the transmission When the signal passes through an amplifier normally provided on the line 6, the signal is blocked by an internal filter circuit and is not transmitted to the terminal side.

However, in order to remove such unnecessary signals, a signal 400 is provided between the mixing circuit 44 and the directional coupler 56.
A band-pass filter that selectively allows only the transmission satellite signal in the MHz band may be provided. Next, the up-converter 30 serves as a local oscillating means according to claim 6, wherein the oscillation circuit (VC
O) 62 is provided. Then, similarly to the downconverter 20 described above, the output from the VCO 62 (the same high-frequency signal in the 1.4 GHz band as the VCO 42 on the downconverter 20 side) and the 400 MHz transmitted from the downconverter 20 via the transmission line 6. The transmission satellite signal is mixed with the transmission satellite signal of the band in a mixing circuit 64 including, for example, a well-known double-balanced mixer.
The frequency is converted into a 1 GHz band satellite reception signal in a so-called upper local area. The mixing circuit 64
This corresponds to the mixing means described in claim 6.

In the up converter 30, the transmission line 6 on the head end 2 side of the mixing circuit 64 is
A branch circuit 68 for branching a part of the signal transmitted from the head end 2 is provided. The transmission signal branched by the branching circuit 68 is input to a filter circuit (a band-pass filter having a center frequency of 69.5 MHz) 69 that allows only the reference signal transmitted from the down converter 20 to pass therethrough. By
A reference signal is extracted. The branch circuit 6
8 and the filter circuit 69 function as reference signal extracting means.

Similarly to the down converter 20, the up-converter 30 also functions as a PLL circuit (oscillation frequency control means according to claim 6) for controlling the oscillation frequency of the VCO 62 so that the high-frequency signal output from the VCO 62 A frequency dividing circuit 66 for dividing by a frequency ratio, and a filter circuit 69
Frequency dividing circuit 7 for dividing the reference signal passing through by a predetermined frequency dividing ratio
0 and the phase of the output signal from each of the frequency dividers 66 and 70, and a phase comparator 72 for generating a signal corresponding to the phase difference.
And a loop filter 74 for generating a second control voltage. The dividing ratio of the dividing circuits 66 and 70 is
Frequency divider circuits 46 and 50 on the down converter 20 side, respectively.
It is set to the same frequency division ratio as.

As a result, in the up-converter 30, the oscillation frequency of the VCO 62 is
Using the reference signal transmitted from the VCO 42, the oscillation frequency of the VCO 42 of the down converter 20 can be matched. Therefore, in the up-converter 30, the original satellite reception signal before frequency conversion by the down-converter 20 can be restored with high accuracy from the transmission satellite signal transmitted from the down-converter 20, and this restored satellite reception signal can be restored. By further outputting the signal to the BS tuner 26 on the terminal side, the desired B
S broadcast signals can be received.

As described above, the CATV of this embodiment is
In the system, a 1 GHz band satellite reception signal output from the BS antenna 18 is transmitted to the head end 2 side by 40
By providing a downconverter 20 for converting the frequency into a transmission satellite signal in the 0 MHz band and providing an upconverter 30 on the transmission line on the subscriber side for converting the frequency of the transmission satellite signal back to the original satellite reception signal, Is transmitted to the subscriber terminal device 4 with low loss.

Each of the converters 20 and 30 has VCOs 42 and 62 for generating high-frequency signals for frequency conversion,
A so-called PLL circuit for controlling the oscillation frequency is provided so that the oscillation frequency of the VCOs 42 and 62 can be controlled by the operation of the PLL circuit. However, the oscillation frequency of the VCOs 42 and 62 is controlled by each PLL circuit. Is generated by a reference oscillation circuit 48 provided in the down-converter 20, and the reference signal generated by the reference oscillation circuit 48 is transmitted to the up-converter 30 through the transmission line 6, thereby increasing the Converter 30
The side can share the reference signal.

Therefore, according to the CATV system of this embodiment, not only can the satellite reception signal be transmitted with low loss, but also the frequency of the high frequency signal used by each converter 20 and 30 for frequency conversion can be matched. Become
The upconverter 30 can restore the original satellite reception signal from the transmission satellite signal with extremely high accuracy.

Further, since it is not necessary to provide the reference oscillation circuit 48 in the up-converter 30, the up-converter 30 can be provided at a low cost, thereby reducing the financial burden on the subscriber and extending to the CATV system. Can be increased.

As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, and various embodiments can be adopted. For example, in the above embodiment,
Although one oscillation circuit (reference oscillation circuit 48) is used as the reference signal generation means provided in the down converter 20, the output from the reference oscillation circuit 48 is used as the reference signal generation means as shown in FIG. (69.5M
Hz) is used as a carrier wave, and is synchronized with an output from an oscillator 58 that generates a 1 kHz sine wave, and is configured using an FM modulation circuit 60 that performs frequency shift by a predetermined frequency shift amount (a so-called deviation: for example, 50 kHz). May be.

That is, the down converter 20 shown in FIG.
In, a modulation signal (FM wave) obtained by FM-modulating a 69.5 MHz carrier with a modulation frequency of 1 kHz and a deviation of 50 kHz is generated as a reference signal.
Since the oscillation frequency of the VCO 42 is input to the phase comparator 52 via the frequency dividing circuit 50, the oscillation frequency of the VCO 42 also fluctuates according to the frequency shift of the reference signal.
Thus, a transmission satellite signal obtained by frequency-converting the satellite reception signal with the FM wave is transmitted onto the transmission line 6.

In this case, the reference signal composed of the FM wave is sent out onto the transmission line 6 via the directional coupler 56 and transmitted to the up-converter 30 as it is, as in the above-described embodiment. Filter circuit 69 (bandpass filter) for extracting reference signal provided in converter 30
Is set in accordance with the frequency shift amount of the reference signal, the VCO 6
The oscillation frequency of the VCO 4 of the down converter 20 is also
It will fluctuate similarly to 2.

Therefore, as shown in FIG. 3, the oscillator 5 for setting the modulation frequency to the down converter 20 of the above embodiment is used.
8 and the FM modulation circuit 60, and the upconverter 3
By setting the signal pass bandwidth of the 0-side filter circuit 69 in accordance with the frequency shift of the reference signal, each of the converters 20 and 30 converts the high-frequency signal for frequency conversion using the reference signal composed of the FM wave. Even if it is generated, the same effect as the above embodiment can be obtained.

Further, by using the frequency-modulated FM wave as the reference signal, the down converter 2
The transmission satellite signal frequency-converted at 0 also shifts in frequency similarly to the reference signal. Therefore, the transmission satellite signal is in a state where a kind of scrambling is applied to the satellite reception signal, and a person who does not have an up-converter can convert the transmission satellite signal into a satellite reception signal using, for example, a commercially available converter. Thus, even if an attempt is made to illegally receive satellite broadcasts, satellite broadcasts cannot be received. If the down converter 20 shown in FIG. 3 is used, such illegal acts can be prevented.

As described above, since the down converter 20 shown in FIG. 3 functions as a scrambler, it is not necessary to use an expensive scrambler generally used in the past to prevent fraud.
A CATV system that can prevent unauthorized reception of satellite broadcasting can be realized at low cost.

When the frequency modulation signal is used as the reference signal as described above, the modulation frequency at the time of frequency modulation is cut off by the loop filters (low-pass filters) 54 and 74 constituting the PLL circuits in the converters 20 and 30. Must be lower than the frequency. This is because if the modulation frequency is higher than the cutoff frequencies of the loop filters 54 and 74, the oscillation frequency of the VCO 42 cannot be made to follow the reference signal, and so-called unlocking occurs.

The deviation may be set in consideration of the following points when the satellite receiving antenna receives a transmission radio wave from an artificial satellite that performs digital broadcasting. That is, since digital broadcasting is a kind of phase modulation system, depending on the capability of the demodulation digital chip, if the frequency (phase) component is disturbed, the bit error rate of data increases. Usually, as a desirable performance, the bit error rate is equal to or less than “10 ⁻⁹ ”. Therefore, if the bit error rate increases more than this, demodulation of video data becomes gradually difficult. , And cannot be demodulated.

Further, since the desirable standard of the residual FM of the satellite tuner for receiving the satellite broadcast is 1 kHz or less, the deviation of the reference signal composed of the FM wave is 1 kHz.
If the value is set to a value sufficiently higher than kHz, the above-described scramble effect can be obtained. It cannot be increased.

In consideration of this point, the optimum deviation with respect to the modulation frequency was experimentally obtained.
As shown in FIG. 4, the higher the modulation frequency, the smaller the deviation. For example, if the modulation frequency is set to about 4 kHz, the deviation can be set to a narrow range of about 12 kHz, but the modulation frequency is set to 500 kHz.
It has been found that when the frequency is set to about Hz, the deviation must be set to about 80 kHz or more. The non-reproducible line shown in FIG. 4 indicates a line where video data cannot be reproduced with an increase in the bit error rate of the data.

Therefore, in a CATV system that receives a transmission radio wave from an artificial satellite that performs digital broadcasting and transmits it to the terminal side, when using an FM wave as a reference signal, it uses the experimental data shown in FIG. , FM wave modulation frequency and deviation may be set.

Although the above description is for the case where an FM wave is used as a reference signal, the above-described scrambling effect can be obtained even when a PM wave obtained by phase-modulating a carrier wave is used for the reference signal. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a configuration of an entire CATV system according to an embodiment.

FIG. 2 is a block diagram illustrating a configuration of a down converter and an up converter according to the embodiment.

FIG. 3 is a block diagram illustrating another configuration example of a down converter and an up converter.

FIG. 4 is an explanatory diagram illustrating a method of setting FM wave characteristics when a frequency modulation signal (FM wave) is used as a reference signal.

[Explanation of symbols]

2 head end, 4 subscriber terminal device, 6 transmission line, 12 VHF antenna, 14 UHF antenna, 1
6 signal processing circuit, 18 BS antenna, 20 down converter, 22 mixer, 26 tuner, 28
... TV receiver, 30 ... Up converter, 42,62
... VCO, 44, 64 ... mixed circuit, 46, 50, 66,
70 frequency divider circuit, 48 reference oscillation circuit, 52, 72 phase comparator, 54, 74 loop filter, 56 directional coupler, 58 oscillator, 60 FM modulator circuit, 68 branch circuit, 69 ... Filter circuit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyotaka Oyama 80, Nojo, Asada-cho, Nisshin-shi, Aichi Pref. 72) Inventor Hiroyoshi Konishi 80 Nogami, Asada-cho, Nisshin-shi, Aichi F-term (reference) in Maspro Denko Corporation 5C025 AA04 AA06 5C056 FA02 FA05 FA11 HA01 HA04 HA13 5C064 BA01 BB05 BC11 BC16 BC21 BD08

Claims (6)

[Claims] A radio wave transmitted from an artificial satellite is received, and the received radio wave is transmitted at a predetermined frequency lower than an original frequency and higher than a broadcast frequency of a VHF band and a UHF band allocated to terrestrial television broadcasting. A head end is provided with a satellite receiving antenna that converts the frequency into a satellite receiving signal in a frequency band and outputs the signal. A plurality of satellite receiving signals from the satellite receiving antenna and other television broadcast signals are transmitted via a common transmission line. In the CATV system transmitting to the subscriber terminal of the above, on the head end side, the satellite reception signal from the satellite reception antenna, in the frequency domain from VHF band to UHF band assigned for the television broadcast signal, and,
A down-converter for converting the frequency into a transmission satellite signal in a predetermined frequency band that does not overlap with the television broadcast signal and transmitting the signal on the transmission line is provided, and transmitted from the head end to the transmission line on each subscriber side. By performing an up-converter for frequency-converting the transmitted satellite signal for transmission to an original satellite reception signal output from the satellite reception antenna and transmitting the signal to the subscriber terminal, the satellite reception signal A predetermined transmission that enables transmission with low loss from the head end to each subscriber side terminal and that can be transmitted in a down direction from the head end to the subscriber side terminal via the transmission line in the down converter. A reference signal generating means for generating a reference signal in a frequency band, and a reference signal transmitting means for transmitting the reference signal generated by the reference signal generating means onto the transmission line. By providing a stage and providing a reference signal extracting unit for extracting the reference signal transmitted from the head end side in the upconverter, the downconverter and the upconverter are provided, and the reference signal generating unit is provided. C. The frequency conversion of each of the satellite reception signal and the transmission satellite signal can be performed by using the generated common reference signal.
ATV system. 2. The CATV system according to claim 1, wherein the reference signal is a modulated signal obtained by frequency-modulating or phase-modulating a carrier having a predetermined frequency. 3. The frequency of the reference signal is set to a lower frequency in a frequency band that can be transmitted in a downstream direction via the transmission line. The CATV system as described. 4. The CAT according to claim 1, wherein:
In the V system, a down converter provided on the head end side, a reference for generating a reference signal of a predetermined frequency band that can be transmitted in a downstream direction from the head end to the subscriber side terminal via the transmission line. Signal generation means, local oscillation means for generating a high-frequency signal for frequency-converting the satellite reception signal into the transmission satellite signal, and an oscillation frequency of the local oscillation means based on a reference signal from the reference signal generation means. Oscillation frequency control means for controlling; mixing the high frequency signal from the local oscillation means with the satellite reception signal to convert the frequency of the satellite reception signal into the transmission satellite signal, and transmit the signal on the transmission line. Means, and reference signal sending means for sending a reference signal generated by the reference signal generating means onto the transmission line. Down converter that. 5. The reference signal generation means for frequency-shifting a carrier having a constant frequency by a predetermined amount by a predetermined amount in a predetermined period.
M modulation circuit, and FM generated by the FM modulation circuit
The down converter according to claim 4, wherein a modulated signal is output as the reference signal. 6. The CAT according to any one of claims 1 to 3,
In the V system, an upconverter provided on a transmission line on each subscriber side, a reference signal extracting means for extracting the reference signal transmitted from the downconverter via the transmission line; Local oscillation means for generating a high-frequency signal for frequency-converting the transmission satellite signal transmitted via the transmission line into an original satellite reception signal; extracting the oscillation frequency of the local oscillation means with the reference signal An oscillation frequency control means for controlling based on the reference signal extracted by the means, and the transmission satellite signal is converted into an original satellite reception signal by mixing the high frequency signal from the local oscillation means and the transmission satellite signal. Mixing means for converting the frequency and sending the converted signal to the subscriber terminal.