JP2902282B2 - CATV level adjuster - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV level adjuster for adjusting a frequency characteristic and a level of a signal transmitted through a cable of a CATV system.

[0002]

2. Description of the Related Art A multi-channel signal such as a coaxial cable or the like is used to transmit signals over multiple channels, such as countermeasures against poor viewing in difficult-to-receive areas and provision of information by connection with a voluntary broadcast or a central processing unit (CPU). CATV (Cable Televi) that distributes transmitted television signals to subscriber terminals
sion) The installation of the system is underway.

An outline of the CATV system will be described with reference to FIG. In this figure, a plurality of trunk branch amplifiers (TBA) 101 are inserted into a trunk line 102 with a span a or a span b. This TBA101
Amplifies the CATV signal to a predetermined level and branches it to the branch trunk 103, and outputs the CATV signal to the succeeding trunk 102. In this figure, only the branch trunks 103 branched by the TBA 101 are shown, but a plurality of branch trunks are branched from each TBA 101.

[0004] The branch trunk line 103 is connected to a plurality of cascade-connected branch units 104, an extension amplifier (EA) 105 for amplifying a CATV signal, and a plurality of branch units 104 following the extension amplifier 105. I have. The CATV signals split by the plurality of splitters 104 are input to the receivers of each subscriber. This extension amplifier 105 is C
Amplification is performed so that the ATV signal becomes a predetermined level.
Incidentally, the trunk line 102 and the branch trunk line 103 are generally configured by laying a coaxial cable, and it is known that the cable loss of the coaxial cable is approximately proportional to the square root of the transmission frequency. Therefore, the signal transmitted through the coaxial cable has a frequency characteristic falling to the right as shown in FIG. However, in FIG. 8, the horizontal axis is frequency, and the vertical axis is loss.

Conventionally, the main branch amplifier 101 and the extension amplifier 105 are provided with a frequency characteristic rising to the right as shown in FIG. 9 and adjusted so that the frequency characteristic of a signal input to these amplifiers becomes a specified input level. I have. However, for example, the main branch amplifier 101 inserted into the main line 102 is set up with poles at predetermined distances. However, there are places where poles cannot be built depending on the location. Cannot always be a constant distance. For example, as shown in FIG. 7, the span of the main line 102 between the main branch amplifiers 101 is a or b.
And a different span.

However, the length of the trunk line 102 cannot be longer than a predetermined length determined by design, and is set shorter. This is because the maximum transmission distance is determined according to the maximum output level of the main branch amplifier 101, and the design length is determined according to this distance. This is because if set, an appropriate signal level cannot be guaranteed. Therefore, the input of the trunk branch amplifier 101 may exceed the prescribed level, but does not fall below the prescribed level. To adjust the input of the trunk branch amplifier 101 to the prescribed level, A BON (Building-out Network) circuit that simulates the frequency characteristics of a coaxial cable can be used as a level adjuster.

Next, an extension amplifier 1 using a BON circuit is used.
FIGS. 10 to 12 show how the frequency characteristics of FIG.
This will be described with reference to FIG. FIG. 10 shows a circuit portion for adjusting the frequency characteristics of the extension amplifier 105. In this figure, reference numeral 202 denotes an amplification unit in the extension amplifier 105,
In front of the amplifying unit 202, four BON circuits 201-1 to 201-4 that give different passing losses are connected. FIG. 11 shows the frequency characteristics of these BON circuits 201-1 to 201-4. A of this figure is the BON circuit 2
01-1, which is the frequency characteristic of the transmission band,
1 has a frequency characteristic of approximately -0.5 (accurately, -0.483) dB, and a frequency characteristic of a downward slope that attenuates by -1 dB at the high frequency band f2 of the transmission band.
, Which is approximately − at the low frequency f1 of the transmission band.
The frequency characteristic is 1 (accurately -0.966) dB, and a right-downward frequency characteristic attenuated by -2 dB at the high frequency f2 of the transmission band.

FIG. 3C shows a BON circuit 201-3.
, Which is approximately − at the low frequency f1 of the transmission band.
2 (accurately -1.932) dB, which is a frequency characteristic of the lower right which attenuates by -4 dB at the high frequency f2 of the transmission band. FIG. 4D shows the frequency characteristic of the BON circuit 201-4. About -4 (accurately -3.864) db at the low frequency f1 of the transmission band and -8 at the high frequency f2 of the transmission band.
The BON circuits 201-1 to 201-4 have a frequency characteristic of decreasing to the right and attenuating by dB.
A switch for connecting a through circuit to each BON circuit in parallel is provided. In this case, for example, the frequency f1 is set to 70 MHz and the frequency f2 is set to 300 MHz.

[0009] Here, it is assumed that the frequency characteristic of the branch output of the trunk branch amplifying unit 101 is a characteristic on the upper right as shown in FIG. 12A, and the cable loss of the branch trunk 103 is shown in FIG.
As shown in FIG.
If the loss of 4 is neglected, the input level characteristic of the extension amplifier 105 has a frequency characteristic that rises to the right as shown in FIG. At this time, the input level of the extension amplifier 105 is 80 dB.
Suppose that it is defined as flat, and +
Assume that the input has exceeded the input by +4 dB at 2 dB and frequency f2.

Therefore, only the BON circuit 201-3 of the BON circuit provided in front of the amplifying unit 202 is inserted, and the other BO
When the N circuit is passed through, approximately -2 at the low frequency f1.
Since the -4 dB signal is attenuated in dB and the high frequency band f2, 8 defined as shown in FIG.
It can be almost corrected to a flat frequency characteristic of 0 dB. As described above, by selecting and inserting one or a plurality of BON circuits 201-1 to 201-4 in front of the amplifying unit 202 using the switches, the attenuation from -1 dB to -15 dB at the frequency f2 is achieved. Can be given to the signal, and the frequency characteristic of the signal can be corrected flat even if the length of the branch trunk 103 is shortened.

[0011]

However, in a branch trunk system, the splitter 104 gives a flat loss to the signal, and the number of the splitters 104 is not always constant but varies depending on the number of subscribers. Is not always constant, and the span c of the branch trunk 103 that gives a signal a cable loss substantially proportional to the square root of the transmission frequency is also
Each is different depending on the installation mode. As described above, the frequency characteristics of the signal input to the extension amplifier 105 have different slopes depending on variables such as the number of the branching devices 104 and the length of the branch trunk 103. This situation will be described with reference to the example shown in FIG.

For example, the frequency characteristic of the branch output of the main branch amplifier 101 is a frequency characteristic that rises to the right as shown by a.
The cable loss of the branch trunk line 103 of the span up to 5 and the loss due to the branching device 104 are, as shown in FIG. It is assumed that the characteristic is 1. Then, the frequency characteristic of the signal input to the extension amplifier 105 is the input level characteristic NO. 1, the input level characteristic NO. Although 1 has a flat characteristic, its level is higher than a specified level, so that the extension amplifier 105 may be saturated and the signal may be distorted.

Further, the length of the branch trunk 103 between the trunk branch amplifier 101 and the extension amplifier 105 changes, and the number of the branching devices 104 increases. As shown in FIG. . 2, the frequency characteristic of the signal input to the extension amplifier 105 is the input level characteristic NO. As shown in FIG. Therefore, the input level characteristics NO. 1 and the input level characteristics NO. It is necessary to compensate the frequency characteristic of No. 2 with an equalizer to make it 80 dB flat which is a specified input. For this purpose, it is necessary to insert an attenuator having a flat frequency characteristic or an equalizer circuit having a frequency characteristic falling to the left. . However, in the configuration shown in FIG. 10, only the BON circuit having the frequency characteristic of the lower right is provided.
It cannot be corrected to a dB flat frequency characteristic.

In order to solve this, a circuit preceding the amplifying unit 202 is set as a plug-in system, and an attenuator, a BON
So-called reverse B having the reverse characteristics of the circuit or BON circuit
It is conceivable that the ON circuit is a plug-in unit, but in this case, it is necessary to change the base unit in order to use the plug-in system, and it is necessary to change the frequency characteristics and Since the amount of attenuation generally does not always match the calculation on the desk, it is necessary to prepare plug-in units of several types of frequency characteristics and the amount of attenuation in advance. For this reason, there arises a problem that the cost increases and the operation of adjusting the frequency characteristics becomes complicated. Accordingly, an object of the present invention is to provide a CATV level adjuster capable of continuously changing the frequency characteristics of the direction and level of the slope.

[0015]

In order to achieve the above object, according to the present invention, a low pass loss in a transmission band is fixed, and a slope of a frequency characteristic of the pass loss in the entire transmission band can be continuously varied. A first slope tilt circuit, a second slope tilt circuit in which a pass loss in a high band of a transmission band is fixed, and a slope of a frequency characteristic of the pass loss in the entire transmission band can be continuously varied, the first slope tilt circuit, and the first slope tilt circuit. A CATV level adjuster is constituted by selecting means for selecting any one of the second slope tilt circuit.

[0016]

According to the present invention, the slope of the selected first slope tilt circuit and the selected second slope tilt circuit is changed. In the first slope tilt circuit, the frequency characteristic of the entire level adjuster is decreased from the frequency characteristic rising right to the right. , And the second slope tilt circuit can continuously vary the frequency characteristic of the entire level adjuster from the frequency characteristic rising left to the frequency characteristic falling left. In addition, by adjusting the amount of attenuation, the level can be adjusted. For this reason, if a level adjuster is provided in front of the extension amplifier, the frequency characteristic and level of the CATV signal input to the extension amplifier can be set to a specified level and flat frequency characteristics.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A C provided with a CATV level adjuster of the present invention
An outline of the ATV system is shown in FIG. In this figure,
A plurality of trunk branch amplifiers (TBA) 1 are inserted in the trunk 2 at predetermined intervals. The amplifying unit of the TBA 1 amplifies the CATV signal to a predetermined level, branches the signal to the branch trunk 3, and outputs the CATV signal to the following trunk 2. In this figure, only the branch trunk line 3 branched by the TBA 1 is shown.
A plurality of branch trunks are branched from A1.

The branch trunk 3 has a plurality of cascade-connected branch units 4, an extension amplifier (EA) 6 for amplifying a CATV signal, a plurality of branch units 4 following the extension amplifier 6, and an extension amplifier. 6 is provided with a CATV level adjuster 5. The CATV level adjuster 5 adjusts the frequency characteristic of the signal input to the extension amplifier 5 flat by setting its frequency characteristic to a predetermined slope, and adjusts the level to a specified level. . The CATV signals split by the plurality of splitters 4 are input to the receivers of each subscriber.
The extension amplifier 5 performs amplification so that the CATV signal becomes a predetermined level.

Next, the CATV level adjuster 5 of the present invention.
2 is shown in FIG. 2, and the level adjuster 5 will be described with reference to FIG. In FIG. 2, reference numeral 11 denotes a first slope tilt circuit having a fixed transmission loss at a low frequency f1 of the transmission band and capable of continuously changing the slope of the frequency characteristic over the entire transmission band from upper right to lower right. Reference numeral 12 denotes a high frequency f2 of the transmission band.
Is a second slope tilt circuit in which the pass loss is fixed and the slope of the frequency characteristic over the entire transmission band can be continuously varied from the left up to the left down.
Slope tilt circuit 11 and second slope tilt circuit 12
And the input terminal 14 and the output terminal 1
5 is a slide switch connected to the switch.

Therefore, in the illustrated level adjuster 5, the CATV signal input to the input terminal 14 is supplied to the contact a of the slide switch 13 via the coupling capacitor C11. In this case, when the slide switch 13 is switched to the position shown in the figure, the CATV signal is output from the contact b.
Is input to the first slope tilt circuit 11 via the
The slope of the frequency characteristic of the slope tilt circuit 11 is CATV
Will be given to the signal. In this state, the slope of the frequency characteristic of the first slope tilt circuit 11 is changed so that the frequency characteristic of the CATV signal becomes flat. At this time, the frequency characteristic of the first slope tilt circuit 11 is adjusted while monitoring the frequency characteristic by connecting a monitor circuit to the monitor terminal 16 connected to the output line via the capacitor C13.

Next, by switching the slide switch 13 to connect the contacts a and c and connect the contacts d and f to select the second slope tilt circuit 12, a CATV signal is obtained. Is input to the second slope tilt circuit 12 via the contact c, so that the slope of the frequency characteristic of the second slope tilt circuit 12 is given to the CATV signal. Then, in this state, the slope of the frequency characteristic of the second slope tilt circuit 12 is varied so that the frequency characteristic of the CATV signal becomes flat. At this time,
A monitor circuit is connected to the monitor terminal 16 connected to the output line via the capacitor C13, and the frequency characteristic of the second slope tilt circuit 12 is adjusted while monitoring the frequency characteristic. The second slope tilt circuit 12 differs from the first slope tilt circuit 11 in that the high frequency f
Since the passage loss in 2 is fixed, a different level adjustment can be performed.

Next, detailed circuits of the first slope tilt circuit 11 and the second slope tilt circuit 12 will be described.
FIG. 3 is a circuit diagram of the first slope tilt circuit 11, in which a first inductor L1 connected between an input terminal 21 and an output terminal 22 and a first resistor R1 connected in parallel to the inductor L1 are shown. , A variable resistor R3 and a fourth resistor R4 connected in series between the output terminal 22 and the ground, a capacitor C1 connected between the input terminal 21 and the variable resistor terminal of the variable resistor R3, and the capacitor C1. , A second capacitor C2 connected between the input terminal 21 and the ground, a connection point between the input terminal 21, the variable resistor R3, and the fourth resistor R4. And an inductor L2 connected between them.

FIG. 4 shows the frequency characteristics of the first slope tilt circuit 11. As shown in this figure, the variable resistor R3
By sliding the variable resistance terminal of (a) to vary its resistance value, the flat frequency characteristic shown in (a) is centered on FIG.
Alternatively, it can be continuously changed in the vertical direction as shown in c. Therefore, by adjusting the variable resistor R3 according to the inclination characteristics of the frequency axis of the signal applied to the input terminal 21, the frequency characteristic of the signal can be adjusted flat.

The loss amount of the flat characteristic a and the variable amount of the inclination characteristic shown by b and c can be varied in a desired variable range by adjusting the first resistor R1, the second resistor R2, and the fourth resistor R4. Can be set to In this case, since the variable range changes in the vertical direction around the flat characteristic a, the variable range increases when the loss amount of the flat characteristic a increases, and when the loss amount of the flat characteristic a decreases, the variable range changes. The range can be reduced. Further, the attenuation of the frequency signal above the frequency (f2) in the high band of the transmission band can be increased by the second capacitor C2. In this example, the lower frequency f1 of the transmission band is 70 MHz,
Although the high frequency f2 is set to 300 MHz, the present invention is not limited to this, and a desired transmission band can be set.

Next, a circuit diagram of the second slope tilt circuit 12 is shown in FIG. In this figure, a third capacitor C3 connected between an input terminal 31 and an output terminal 32
And a fifth resistor R connected in parallel with the capacitor C3.
5, a variable resistor R7 and an eighth resistor R8 connected in series between the output terminal 32 and the ground, and a third inductor L3 connected between the input terminal 31 and the variable resistor terminal of the variable resistor R7. A sixth resistor R6 connected in parallel with the inductor L3, a fourth inductor L4 connected between the input terminal 31 and the ground, an input terminal 31, a variable resistor R7, and an eighth resistor R8. And a fourth capacitor C4 connected between the node and the connection point.

FIG. 6 shows the frequency characteristics of the second slope tilt circuit 12 configured as described above. As shown in this figure, the variable resistor terminal of the variable resistor R7 is slid to change its resistance value, thereby fixing the pass loss in the high band of the transmission band around the flat frequency characteristic shown in a. The transmission loss in the lower band of the transmission band can be continuously varied in the vertical direction as shown in FIG. Therefore,
By adjusting the variable resistor R7 in accordance with the tilt characteristics on the frequency axis of the signal input to the input terminal 31, the frequency characteristics of the signal can be adjusted flat.

The loss amount of the flat characteristic a and the variable amount of the inclination characteristic shown by b and c can be varied within a desired variable range by adjusting the fifth resistor R5, the sixth resistor R6, and the eighth resistor R8. Can be set to In this case, since the variable range changes in the vertical direction around the flat characteristic a, the variable range increases when the loss amount of the flat characteristic a increases, and when the loss amount of the flat characteristic a decreases, the variable range changes. The range can be reduced. Further, the fourth inductor L4 can increase the amount of attenuation of the frequency signal below the lower frequency (f1) of the transmission band as shown in the figure. In this example, the lower frequency f1 of the transmission band is used.
Is 70 MHz and the high frequency f2 is 300 MHz. However, the present invention is not limited to this, and a desired transmission band can be set.

Such a first slope tilt circuit 11
In order to adjust the frequency characteristic of the CATV signal using the second slope tilt circuit 12, for example, when the attenuation amount to be attenuated at the low frequency f1 of the CATV signal is set as a reference, the first slope tilt circuit Select 11 and
After adjusting the attenuation amount of the flat characteristic to the attenuation amount at which the CATV signal should be attenuated, the level and the frequency characteristic of the CATV signal can be adjusted by adjusting the variable resistor R3 so that the frequency characteristic of the CATV signal becomes flat. it can. When the amount of attenuation to be attenuated at the high frequency f2 is set as a reference, the second slope tilt circuit 12 is selected, and
After adjusting the attenuation of the flat characteristic to the attenuation at which the CATV signal should be attenuated, the level and frequency characteristics of the CATV signal can be adjusted by adjusting the variable resistor R7 so that the frequency characteristic of the CATV signal becomes flat. it can.

[0029]

Since the present invention is constructed as described above, the slope of the selected first slope tilt circuit and the second slope tilt circuit is set to the right, and the first slope tilt circuit sets the frequency characteristic of the entire level adjuster to the right. The frequency characteristics can be continuously varied from the rising frequency characteristics to the falling frequency characteristics. The second slope tilt circuit continuously varies the frequency characteristics of the entire level adjuster from the rising left frequency characteristics to the falling left frequency characteristics. can do. In addition, by adjusting the amount of attenuation, the level can be adjusted. For this reason, if a level adjuster is provided in front of the extension amplifier, the frequency characteristics and the level of the CATV signal input to the extension amplifier can be set to desired frequency characteristics of a specified level.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a CATV system using a level adjuster of the present invention.

FIG. 2 is a block diagram showing a level adjuster according to the present invention.

FIG. 3 is a circuit diagram of a first slope tilt circuit.

FIG. 4 is a frequency characteristic diagram of a first slope tilt circuit.

FIG. 5 is a circuit diagram of a second slope tilt circuit.

FIG. 6 is a frequency characteristic diagram of a second slope tilt circuit.

FIG. 7 is a schematic diagram of a conventional CATV system.

FIG. 8 is a frequency characteristic diagram of a coaxial cable.

FIG. 9 is a frequency characteristic diagram of the amplifier.

FIG. 10 is a block diagram for adjusting a conventional frequency characteristic.

FIG. 11 is a frequency characteristic diagram of the BON circuit.

FIG. 12 is a diagram illustrating a mode of adjusting a frequency characteristic.

FIG. 13 is a diagram illustrating a mode of adjusting a frequency characteristic.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1,101 Trunk branch amplifier 2,102 Trunk 3,103 Branch trunk 4,104 Branch 5 Level adjuster 6,105 Extension amplifier 11 First slope tilt circuit 12 Second slope tilt circuit 13 Slide switch 14,21,31 Input Terminal 15, 22, 32 Output terminal 16 Monitor terminal 201-1 to 201-4 BON circuit R1 to R8 Resistance C1 to C4, C11 to C13 Capacitor L1 to L4 Inductor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 7/10 H04N 7/16

Claims (2)

(57) [Claims] An input terminal, an output terminal, a first slope tilt circuit in which a low pass loss in a transmission band is fixed, and a slope of a frequency characteristic of a pass loss in the entire transmission band can be varied, and a high band in a transmission band. And a second slope tilt circuit, wherein the slope of the frequency characteristic of the pass loss in the entire transmission band is variable, and any one of the first slope tilt circuit and the second slope tilt circuit is provided. Switching means for selecting and connecting between the input terminal and the output terminal. 2. The CATV level adjuster according to claim 1, wherein a monitor terminal is connectable to a line connected to the output terminal.