JPH1056347A - CATV amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent decrease in gain and decrease in C/N from being caused even when one kind of amplifier is used. SOLUTION: When a CATV system has a 1st frequency band, an equalizer circuit 41 which matches the frequency band is inserted and equalizer circuits 42 and 43 are passed through. When the CATV system has a 2nd frequency band, on the other hand, the equalizer circuit 42 matching the frequency band is inserted and the equalizer circuits 41 and 43 are passed through. Thus, an equalizer circuit matching the frequency band of the CATV system is selected to prevent the gain and C/N from decreasing. Amplifiers 45 and 47 are wide- band amplifiers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CA which has general versatility used for a terminal system of a CATV system.
It relates to a TV amplifier.

[0002]

2. Description of the Related Art A CATV system is roughly divided into a center system, a transmission system, and a terminal system. Among these, the center system is a part for transmitting a television broadcast program received by a plurality of antennas for receiving a plurality of broadcast waves or a television program independently produced from the center to the transmission system, and the transmission system is transmitted from the center to the transmission system. This is a part for efficiently transmitting the transmitted television broadcast program while suppressing the generation of transmission distortion and noise. The terminal system is a part that draws a television program sent from the transmission system into an apartment house or a detached house and distributes it to each house or each resident.

In a transmission system, a coaxial cable is mainly used, which is divided into a trunk line, a branch line, a branch line, a drop-in line, etc., and a line amplifier suitable for each line is used. It is inserted into the line to compensate for its transmission loss. The amplifier inserted into such a line adjusts the slope of the frequency characteristic of the transmission signal in accordance with the length of the transmission line so that the transmission signal has a flat frequency characteristic at the receiving end of the line, and transmits the signal. ing. As is well known, the transmission loss of a coaxial cable is Δf (f: frequency)
Therefore, the signal in the high frequency band is more attenuated due to the loss than the signal in the low frequency band. For this reason, the amplifier inserted in the line outputs a transmission signal having a frequency characteristic that rises to the right and has a high output level in the high frequency range and a low output level in the low frequency range.

[0004]

However, the coaxial cable may be drawn into the terminal system beyond the prescribed length of the coaxial cable. In such a case, the length of the coaxial cable is longer than the prescribed length. In this case, the attenuation in the high frequency band becomes large, and the frequency characteristic of the signal received by the terminal is not flat, but often becomes the frequency characteristic in which the high frequency band is attenuated. Therefore, in order to solve this problem, an equalizer is conventionally provided in a stage preceding the terminal system amplifier, and the frequency characteristic of the signal is adjusted to be flat by the equalizer. By the way, the transmission frequency band in the CATV system has been expanding more and more in recent years, and the transmission frequency band from the 70 MHz to 450 MHz band has been expanded to the 70 MHz to 550 MHz band and then to the 70 MHz to 770 MHz band.

[0005] Such CAT having different transmission frequency bands.
At present, V systems exist in a mixed state.
In this case, assuming that the operating frequency band of the equalizer is the widest frequency band, 70 MHz to 770 MHz,
It seems that the present invention can be applied to any frequency band of the CATV system. However, when the equalizer is used in a CATV system having a different transmission frequency band, the gain of the signal is reduced, and the C / C is reduced. N decreases. This will be described with reference to FIGS. FIG. 7 shows an example of frequency characteristics of an equalizer for equalizing a signal in a 70 MHz to 550 MHz band.
Naturally, when applied to a CATV system in the Hz to 550 MHz band, desired performance is exhibited.

However, when this equalizer is applied to a CATV system having a narrow transmission frequency band of 70 MHz to 450 MHz, the upper limit of the frequency is 450 MHz.
The level at MHz becomes lower by L1 [dB] as shown. That is, the signal gain is L1 [d
B], and the C / N also decreases accordingly. FIG. 8 shows an example of a frequency characteristic of an equalizer for equalizing a signal in a 70 MHz to 770 MHz band. This equalizer has a transmission frequency band of 70 MHz.
When applied to a CATV system in the z to 770 MHz band, it naturally exhibits the desired performance.

However, when this equalizer is applied to a CATV system having a transmission frequency band of 70 MHz to 450 MHz or a CATV system having a narrow transmission frequency band of 70 MHz to 550 MHz, the level at the upper limit frequency of 450 MHz is increased. Alternatively, the level at the upper limit frequency 550 MHz decreases by L2 [dB] or L3 [dB] as shown in the figure. That is, the gain of the signal is attenuated by L2 [dB] or L3 [dB], and the C / N is also reduced accordingly. In order to prevent such a decrease in gain and a decrease in C / N, it is necessary to prepare a plurality of types of CATV amplifiers in which equalizers suitable for different transmission frequency bands are installed in front of different frequency bands.

When a plurality of types of CATV amplifiers are prepared, there are problems in that the number of types of products increases, the cost increases, and a large storage space for storing the products is required. . Therefore, the present invention provides a CATV amplifier which can use only one kind of product and which does not cause a decrease in gain and C / N even when used in a CATV system of any transmission frequency band. It is intended to provide.

[0009]

In order to achieve the above object, a CATV amplifier according to the present invention is a CATV amplifier used for a terminal system of a CATV system in which various signals including at least a video signal and an audio signal are transmitted. , An equalizer comprising a plurality of equalizer circuits for individually equalizing a plurality of frequency bands having different bandwidths, a wideband amplifier for amplifying an equalized signal, and the CATV
Selecting means for selecting an optimum equalizer circuit from the plurality of equalizer circuits according to a frequency band set in the system. In the CATV amplifier, the operating frequency band of the wideband amplifier covers at least the widest frequency band in the CATV system.

According to the present invention, it is possible to select an optimum equalizer for the transmission frequency band according to the transmission frequency band of the CATV system.
Therefore, even with one type of CATV amplifier, it is possible to prevent a decrease in gain of a received signal and a decrease in C / N.

[0011]

FIG. 1 shows an example of an overall view of a CATV system to which a CATV amplifier according to the present invention is applied.
The CATV system shown in this figure is composed of a center system, a transmission system, and a terminal system of an apartment house or a detached house. In the center system, an in-area receiving antenna 1-1, an out-of-area receiving antenna 1-2, a BS receiving antenna 1-3, a CS receiving antenna 1-4, and the like for receiving various television broadcasts are installed. The television broadcast signal received by the plurality of antennas is input to the head end 2. In the center system, there is provided a studio 3 comprising a TV camera and a microphone, and a studio adjustment room for editing video signals, etc., and a signal of a program independently produced in the studio 3 is input to the head end 2. Have been.

The head end 2 is an amplifier that amplifies various input television signals to a level necessary for sending the signals to a transmission system. The head end 2 also has a function of rearranging channels of various input television signals to channels in the frequency band of the CATV system being constructed. The signal of the predetermined frequency band set to the predetermined level in this way is supplied to the coaxial line 7.
And a main line consisting of a main line amplifier inserted into the coaxial line 7 at a predetermined interval. The transmission signal is amplified to a predetermined level in the trunk distribution amplifier (TDA) 4 and distributed to a plurality of trunks. One distributed transmission signal propagates through the coaxial line 7 and is then distributed to a plurality of distribution lines by a branch amplifier (BA) 5.

Further, another distributed transmission signal propagates through a trunk composed of a coaxial line 7 and a trunk branch amplifier (TBA) 6 inserted into the coaxial line 7 at a predetermined interval. The transmission signal distributed to the distribution line 9 is input to the terminal apartment complex 30. Note that TBA, T
Power is supplied from a power supply 8 to an amplifier such as a DA via a main line. The signal transmitted from the head end 2 is converted into an optical signal by an optical transmitter (E / O) 20 and propagates through an optical fiber cable 21. The optical signal propagated through the optical fiber cable 21 is transmitted to an optical receiver (O /
E) The signal is received at 22 and converted into an electric signal.
3 and a main line composed of a main line amplifier inserted into the coaxial line 23 at a predetermined interval.

The T inserted in the coaxial line 23
The transmission signal branched by the BA is amplified to a predetermined level by the BA 24 inserted into the branch line, and is distributed to a plurality of distribution lines. A plurality of tap-offs 25 are cascade-connected to the distribution wiring.
The service line connected to 5 is drawn into the detached house 31 of the terminal system.

In the terminal apartment complex 30, the transmission signal pulled in via the protector 10 is the CAT of the present invention.
V is amplified to a predetermined level by a relay amplifier 11 provided with an amplifier for V, and the CATV of the present invention is further amplified.
The signal is amplified by the in-building distribution amplifier 13 provided with the power amplifier and transmitted to each resident through a plurality of wall terminals 14. Thereby, each resident of the apartment house 30 can receive the signal transmitted from the head end 2,
By supplying the received signal to a television or the like, desired video and audio can be enjoyed. In the terminal-based detached house 31, the transmission signal pulled in via the protector 26 is the CA of the present invention.
The signal is amplified to a predetermined level by a relay amplifier 27 provided with a TV amplifier, and
Is supplied to the TV 29 installed in each room via the. Thereby, in the detached house 31, the signal transmitted from the head end 2 can be received,
By supplying the received signal to the TV 29,
It is possible to enjoy desired video and audio.

According to the CATV amplifier of the present invention, the CA
Relay amplifier 1 used in terminal system of TV system
It is provided as a down-amplifier in the distribution amplifiers 1 and 27 and the in-building distribution amplifier 13. The downstream amplifiers in the relay amplifiers 11 and 27 have functions of amplifying the transmission signal so as to have a predetermined level and adjusting the frequency characteristics of the received transmission signal. The reason for adjusting the frequency characteristics is as follows. As described above, the frequency characteristics of the transmission signals output from TDA, TBA, and BA are adjusted so that the frequency characteristics of the transmission signals become flat at the receiving end. That is, the transmission signals output from TDA, TBA, and BA are
The level is inclined upward to the right so that the level increases toward the high frequency so that the high frequency is higher than the low frequency.
Thereby, the attenuation of the coaxial cables 7 and 23 whose attenuation amount exhibits the Δf characteristic can be compensated as described above.

Therefore, ideally, the frequency characteristic of the transmission signal received in the terminal system is flat at the receiving end. However, the distance between the BA or TBA and the terminal system differs depending on the location where the apartment house 30 or the detached house 31 is built, and the frequency of the transmission signal received by the terminal system is different because the length of the coaxial cable is different. In many cases, the characteristics do not become flat at the receiving end, but become inclined frequency characteristics. In this case, since the length of the coaxial cable of the terminal system is generally longer than the specified length, the attenuation in the high frequency band increases, and the frequency characteristic has a right-downward slope in which the level gradually decreases from the low frequency band to the high frequency band. Therefore, an equalizer is provided in the downstream amplifiers in the relay amplifiers 11 and 27 and the in-building distribution amplifier 13, and the received transmission signal is made to have required characteristics by the equalizer.

FIG. 2 shows a circuit example showing the configuration of the embodiment of the relay amplifiers 11 and 27, which are the CATV amplifiers of the present invention, and the down-amplifier of the in-building distribution amplifier 13.
In the downstream amplifier shown in FIG.
The transmission signal input via 1 is split by the splitter / mixer 40 to the equalizer EQ side. The split transmission signal is equalized by equalizer circuits 41, 42, and 43 by an equalizer EQ so that its frequency characteristic becomes substantially flat, or the low-frequency level has a frequency characteristic that is lower left than the high-frequency level. Adjusted. Then, the level is adjusted by an attenuator (ATT) 44, and the transmission signal is amplified to a predetermined level in an amplifying unit including a high-band amplifier (AMP) 45, a gain control 46, and a high-band amplifier (AMP) 47. In this manner, the transmission signal having a substantially flat frequency characteristic or a low-frequency level falling to the left from the high-frequency level and having a predetermined level is transmitted to the demultiplexer / mixer 4.
8, and output via the coupling capacitor 49-2.

Next, a detailed circuit example of the equalizer EQ is shown in FIG. The equalizer EQ shown in FIG.
An equalizer circuit 41 for adjusting a frequency characteristic of a transmission signal in a frequency band up to 450 MHz;
An equalizer circuit 42 for adjusting a frequency characteristic of a transmission signal in a frequency band up to MHz, and 70 MHz to 770 MHz.
And an equalizer circuit 43 for adjusting the frequency characteristic of the transmission signal in the frequency band up to the cascade.
The equalizer circuits 41, 42, and 43 are provided with switches SW1, SW2, and SW3, respectively. The switches SW1, SW2, and SW3 allow the equalizer circuits 41, 42, and 43 to pass through or to be inserted into the lines. You have to be able to choose.

For example, when the frequency band of the CATV system in which the relay amplifiers 11 and 27 and the in-building distribution amplifier 13 are installed is set to 70 MHz to 450 MHz, the switch SW1 is switched to the equalizer circuit 41 to switch the equalizer circuit 41. insert. And the switch S
W2 and the switch SW3 are set to the through side, and the equalizer circuits 42 and 43 are set to the through side. Thereby, CAT
70 MHz to 45, which is the frequency band of the V system
The frequency characteristic of the transmission signal set to 0 MHz is equalized by the equalizer 4.
1 can be adjusted. In this case, since the optimum equalizer circuit 41 has been selected, the gain is reduced and C
/ N does not decrease.

When the CATV system in which the relay amplifiers 11 and 27 and the in-building distribution amplifier 13 are installed has a frequency band of 70 MHz to 550 MHz, the switch SW2 is switched to the equalizer circuit 42 to switch the equalizer circuit 42. insert. The switches SW1 and SW3 are set to the through side, and the equalizer circuits 41 and 43 are set to the through side. With this, 70 MHz to 550 MHZ, which is the frequency band of the CATV system,
The frequency characteristic of the transmission signal represented by z can be adjusted by the equalizer 42. In this case, since the optimal equalizer circuit 42 is selected, there is no decrease in gain or C / N.

Further, when the frequency band of the CATV system in which the relay amplifiers 11 and 27 and the in-building distribution amplifier 13 are set is 70 MHz to 770 MHz,
The switch SW3 is switched to the equalizer circuit 43 side to insert the equalizer circuit 43. And the switch SW1
The switch SW2 is set to the through side, and the equalizer circuits 41 and 42 are set to the through side. As a result, the frequency band of 70 MHz to 770 M
The frequency characteristic of the transmission signal set to Hz can be adjusted by the equalizer 43. In this case, since the optimum equalizer circuit 43 is selected, the gain is reduced and the C / N ratio is reduced.
Does not occur. The operating frequency bands of the broadband amplifiers 45 and 47 provided after the equalizer EQ are as follows.
It can cover at least the frequency band of 70 MHz to 770 MHz.

The equalizer circuit 41 comprises coils L1 and L2, capacitors C1 and C2, and resistors R1 and R2, as shown in the figure. The frequency characteristics of the equalizer circuit 41 are shown in FIG. As shown in FIG. 4, the equalizer circuit 41 has a gain at a frequency of 70 MHz and a gain of about 4 dB at a frequency of 70 MHz.
The frequency characteristic is decreasing and rising to the right. The reason why the frequency characteristic is upwardly sloping is that the frequency characteristic of the received transmission signal has a downwardly sloping frequency characteristic that gradually decreases from a low band to a high band as described above. Then, at the upper limit frequency 450 MHz of the frequency band,
Since the loss of the equalizer circuit 41 is set to almost 0 dB, a decrease in the level of the transmission signal and a decrease in the C / N do not occur.

The equalizer circuit 42 includes a coil L3,
FIG. 5 shows the frequency characteristics of the equalizer circuit 42, which is composed of L4, capacitors C3 and C4, and resistors R3 and R4. As shown in FIG. 5, the equalizer circuit 42
For gain at frequency 550 MHz, frequency 7
The frequency characteristic is a right-up frequency in which the gain at 0 MHz is reduced by about 4 dB. The reason why the frequency characteristic is upwardly sloping is that the frequency characteristic of the received transmission signal has a downwardly sloping frequency characteristic that gradually decreases from a low band to a high band as described above. Then, at the upper limit frequency 550 MHz of the frequency band, the equalizer circuit 42
Is almost 0 dB, so that the transmission signal level does not decrease and the C / N does not decrease.

The equalizer circuit 43 includes a coil L5,
FIG. 6 shows the frequency characteristics of the equalizer circuit 43, which is composed of L6, capacitors C5 and C6, and resistors R5 and R6. As shown in FIG. 6, the equalizer circuit 43
For gain at frequency 770 MHz, frequency 7
The frequency characteristic is a right-up frequency in which the gain at 0 MHz is reduced by about 6 dB. The reason why the frequency characteristic is upwardly sloping is that the frequency characteristic of the received transmission signal has a downwardly sloping frequency characteristic that gradually decreases from a low band to a high band as described above. Then, at the upper limit frequency 770 MHz of the frequency band, the equalizer circuit 43
Is almost 0 dB, so that the transmission signal level does not decrease and the C / N does not decrease.

In the above description, three equalizer circuits are included in the equalizer EQ.
It may be configured by four or more equalizers according to the frequency band of the TV system. And when using such a relay amplifier and a ridge distribution amplifier,
An equalizer circuit according to the frequency band of the CATV system to be used may be selected when the relay amplifier is installed. In this case, even when the CATV frequency band is changed after the installation, it can be dealt with by switching the equalizer circuit. The frequency characteristics of the equalizer circuit described above are merely examples, and the present invention is not limited to this, and can be changed according to the mode of the CATV system.

[0027]

As described above, the present invention is configured as described above, so that even with one type of CATV amplifier, an optimum equalizer for the transmission frequency band can be selected according to the different transmission frequency bands of the CATV system. become. Therefore, it is possible to prevent a decrease in gain of a received signal and a decrease in C / N even with a single type of CATV amplifier.

[Brief description of the drawings]

FIG. 1 shows a CATV to which the CATV amplifier of the present invention is applied.
FIG. 1 is a diagram illustrating an example of an overall view of a system.

FIG. 2 is a diagram showing a circuit example of a configuration of an embodiment of a relay amplifier which is a CATV amplifier of the present invention and a downstream amplifying unit of a distribution amplifier in a building.

FIG. 3 is a diagram showing an example of a detailed circuit of an equalizer in the CATV amplifier of the present invention.

FIG. 4 is a diagram showing a frequency characteristic of an equalizer circuit 41 in the CATV amplifier according to the present invention.

FIG. 5 is a diagram showing a frequency characteristic of an equalizer circuit 42 in the CATV amplifier of the present invention.

FIG. 6 is a diagram showing a frequency characteristic of an equalizer circuit 43 in the CATV amplifier of the present invention.

FIG. 7 is a diagram for describing equalization using an equalizer that equalizes a signal in a 70 MHz to 550 MHz band.

FIG. 8 is a diagram for explaining equalization using an equalizer that equalizes a signal in a 70 MHz to 770 MHz band.

[Explanation of symbols]

 1-1 Receiving antenna in area 1-2 Receiving antenna outside area 1-3 BS receiving antenna 1-4 CS receiving antenna 2 Head end 3 Studio 4 Trunk distribution amplifier (TDA) 5, 24 Branch amplifier (BA) 6 Trunk branch amplifier (TBA) 7,23 Coaxial line 8 Power supply 9 Separate wiring 10,26 Protector 11,27 Relay amplifier 13 In-building distribution amplifier 14 Wall terminal 20 Optical transmitter 21 Optical fiber cable 22 Optical receiver 25 Tap-off 28 Home terminal 29 Television 30 Apartment house 31 Detached house 40,48 Demultiplexer / Mixer 41,42,43 Equalizer circuit 44 Attenuator 45,47 Broadband amplifier 46 Gain control 49-1,49-2 Capacitor

Claims (2)

[Claims] 1. A CATV amplifier used in a terminal system of a CATV system in which various signals including at least a video signal and an audio signal are transmitted, comprising: a plurality of equalizer circuits for individually equalizing a plurality of frequency bands having different bandwidths; An equalizer, a wideband amplifier for amplifying an equalized signal, and selecting means for selecting an optimum equalizer circuit from among the plurality of equalizer circuits according to a frequency band set in the CATV system. The amplifier for CATV characterized by the above-mentioned. 2. The CATV amplifier according to claim 1, wherein an operating frequency band of the wideband amplifier covers at least a widest frequency band in the CATV system.