JPH07131776A - Level adjustment device for catv - Google Patents

Abstract

PURPOSE:To obtain the CATV use level adjustment device by varying continuously a frequency characteristic of a level and a direction of a slope. CONSTITUTION:A 1st slope tilt circuit 11 in which a passing loss in a low frequency at a transmission band is fixed and a high frequency passing loss is varied in an increasing/decreasing way and a 2nd slope tilt circuit 12 in which a passing loss in a high frequency at a transmission band is fixed and a low frequency passing loss is varied in an increasing/decreasing way are provided to the adjustment device. Then a slide switch 13 is controlled to connect either of the 1st and 2nd slope tilt circuits 11,12 between an input terminal 14 and an output terminal 15 and the frequency characteristic of either of the selected 1st and 2nd slope tilt circuits 11,12 is varied to adjust the frequency characteristic of a received CATV signal.

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 the frequency characteristic and 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, for transmitting signals over multiple channels, such as measures for difficult-to-view in difficult-to-receive areas and for providing information through independent broadcasting or connection with a central processing unit (CPU) And distributes the transmitted television signals to subscriber terminals.
sion) system is being installed.

An outline of this CATV system will be described with reference to FIG. In this figure, a plurality of trunk line branch amplifiers (TBA) 101 are inserted in a trunk line 102 with a span a or a span b. This TBA101
The amplifying section of amplifies the CATV signal to a predetermined level and branches it to the branch main line 103, and outputs the CATV signal to the subsequent main line 102. However, although only the branch trunk line 103 branched by the TBA 101 is shown in this figure, each TBA 101 branches a plurality of branch trunk lines.

A plurality of branching units 104 connected in cascade, an extension amplifier (EA) 105 for amplifying a CATV signal, and a plurality of branching units 104 subsequent to the extension amplifier 105 are connected to the branch trunk line 103. There is. The CATV signal branched by the plurality of branching units 104 is input to the receiver of each subscriber. This extension amplifier 105 is C
Amplification is performed so that the ATV signal becomes a predetermined level.
By the way, the trunk line 102 and the branch trunk line 103 are generally constructed by laying coaxial cables, and it is known that the cable loss of the coaxial cables is approximately proportional to the square root of the transmission frequency. Therefore, the signal transmitted through the coaxial cable has a frequency characteristic of downward sloping as shown in FIG. However, in FIG. 8, the horizontal axis represents frequency and the vertical axis represents loss.

Conventionally, the trunk branch amplifier 101 and the extension amplifier 105 are provided with the upward-sloping frequency characteristics shown in FIG. 9, and the frequency characteristics of the signals input to these amplifiers are adjusted so as to reach a specified input level. There is. However, for example, the main branch amplifier 101 inserted into the main line 102 is installed with a pole set up at a predetermined distance, but the pole cannot be built in some places, so that the span between the main branch amplifiers 101 is large. Cannot always be a constant distance. For example, as shown in FIG. 7, the span of the trunk line 102 between the trunk line branch amplifiers 101 is a or b.
It may have a different span.

However, the length of the main line 102 cannot be longer than the predetermined length designed, and is set to be short. This is because the maximum transmission distance is determined according to the maximum output level of the trunk line branch amplifier 101, and the designed length is determined according to this distance, so the length of the trunk line 102 is exceeded beyond this length. This is because if set, it becomes impossible to guarantee an appropriate signal level. Therefore, the input of the main line branch amplifier 101 may exceed the predetermined level set in advance, but does not fall below the predetermined level. Therefore, in order to adjust the input of the main line branch amplifier 101 to the predetermined level, A BON (Building-out Network) circuit that simulates the frequency characteristics of the coaxial cable may be used as the level adjuster.

Next, using the BON circuit, the extension amplifier 1
FIG. 10 to FIG. 12 show how the frequency characteristics of 05 are adjusted.
Will be described with reference to. FIG. 10 shows a circuit portion for adjusting the frequency characteristic of the extension amplifier 105. In this figure, reference numeral 202 denotes an amplification unit in the extension amplifier 105,
Four BON circuits 201-1 to 201-4 that give different passage losses are connected in front of the amplification unit 202. FIG. 11 shows the frequency characteristics of these BON circuits 201-1 to 201-4. In this figure, a is the BON circuit 2
The frequency characteristic of 01-1 is the low frequency f of the transmission band.
1 has a frequency characteristic of about -0.5 (correctly -0.483) dB and a downward-sloping frequency characteristic of attenuating by -1 dB at the high frequency f2 of the transmission band.
Is a frequency characteristic of, and is substantially − at the low frequency f1 of the transmission band.
The frequency characteristic is 1 (correctly -0.966) dB, and the frequency characteristic is a downward-sloping frequency that is attenuated by -2 dB at the high frequency f2 of the transmission band.

Further, FIG. 3C shows a BON circuit 201-3.
Is a frequency characteristic of, and is substantially − at the low frequency f1 of the transmission band.
2 (accurately -1.932) dB, and the frequency characteristic is a downward sloping frequency that attenuates -4 dB at the high frequency f2 of the transmission band. FIG. 4D shows the frequency characteristic of the BON circuit 201-4. At the low frequency f1 of the transmission band, approximately -4 (correctly -3.864) db, and at the high frequency f2 of the transmission band -8.
The BON circuits 201-1 to 201-4 have the frequency characteristics of a right-downward direction in which they are attenuated by dB.
A switch for connecting a through circuit in parallel to each BON circuit is provided. In this case, for example, the frequency f1 is 70 MHz and the frequency f2 is 300 MHz.

Here, assuming that the frequency characteristic of the branch output of the main branch branch amplifier 101 is the upper right characteristic as shown in FIG. 12A, the cable loss of the branch main line 103 is shown in FIG.
Assuming that the characteristic is a downward sloping curve as shown in,
When the loss of 4 is neglected, the input level characteristic of the extension amplifier 105 becomes 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.
Assuming that the frequency is flat, + at frequency f1
It is assumed that the input exceeds +4 dB at 2 dB and the frequency f2.

Therefore, only the BON circuit 201-3 of the BON circuits placed in front of the amplification section 202 is inserted and the other BO
When the N circuit is passed through, it is approximately -2 at the low frequency f1.
Since the -4 dB signal is attenuated at the high frequency f2 in dB, the value of 8 is defined as shown in d of 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 switch, attenuation of -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 line 103 is shortened.

[0011]

However, in the branch trunk system, the branching device 104 gives a flat loss to the signal, and the number of the branching device 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 line 103 that gives a signal to the signal a cable loss approximately proportional to the square root of the transmission frequency,
They are made different depending on the installation mode. In this way, the frequency characteristics of the signal input to the extension amplifier 105 have different inclinations of the frequency characteristics according to variables such as the number of branching units 104 and the length of the branch trunk line 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 line branch amplifier 101 is a frequency characteristic that rises to the right as shown by a, and the main line branch amplifier 101 to the extension amplifier 10 are provided.
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. Although it has a flat characteristic as shown in FIG. 1, the input level characteristic NO. Although 1 has a flat characteristic, its level is higher than the specified level, so that the extension amplifier 105 may be saturated and the signal may be distorted.

Further, as the length of the branch trunk line 103 between the trunk line branch amplifier 101 and the extension amplifier 105 changes, the number of branching devices 104 increases, and the loss NO in the right downward direction is increased as shown in FIG. ． 2, the frequency characteristic of the signal input to the extension amplifier 105 has the input level characteristic NO. As shown in FIG. 2, the characteristic is downward sloping. Therefore, the input level characteristic NO. 1 and input level characteristic NO. It is necessary to compensate the frequency characteristic of No. 2 with an equalizer to make it a flat input of 80 dB 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 downward-sloping frequency characteristic. . However, since the configuration shown in FIG.
It cannot be corrected to the frequency characteristic of dB flat.

To solve this, the circuit in front of the amplification section 202 is a plug-in type, and an attenuator and a BON are used.
Circuit or so-called reverse B having the reverse characteristic of the BON circuit
It is considered that the ON circuit is used as a plug-in unit. However, if this is done, it is necessary to change the base unit in order to use the plug-in system, and the frequency characteristics of the plug-in unit required on site and Since the amount of attenuation does not always match the calculation on the desk, it is necessary to prepare in advance plug-in units of several types of frequency characteristics and amounts of attenuation. Therefore, there is a problem that the cost is increased and the work of adjusting the frequency characteristics becomes complicated. Therefore, an object of the present invention is to provide a CATV level adjuster capable of continuously varying the frequency characteristics of the slope direction and level.

[0015]

In order to achieve the above object, according to the present invention, the pass loss in the low band of the transmission band is fixed, and the slope of the 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 the pass loss in the high band of the transmission band is fixed, and the slope of the frequency characteristic of the pass loss in the entire transmission band can be continuously changed, the first slope tilt circuit, and the above The CATV level adjuster is configured by the selecting means that can select either the second slope tilt circuit or the second slope tilt circuit.

[0016]

According to the present invention, the slope between the selected first slope tilt circuit and the second slope tilt circuit is changed from the upward rising frequency characteristic to the right downward slope in the first slope tilt circuit. Can be continuously varied, and the second slope tilt circuit can continuously vary the frequency characteristic of the entire level adjuster from a frequency characteristic of rising to the left to a frequency characteristic of decreasing to the left. In addition, the level can be adjusted by adjusting the attenuation amount. Therefore, if a level adjuster is placed 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 a flat frequency characteristic.

[0017]

EXAMPLE A C provided with a level adjuster for CATV of the present invention
A schematic of the ATV system is shown in FIG. In this figure,
A plurality of trunk line branch amplifiers (TBA) 1 are inserted in the trunk line 2 with a predetermined span. The amplification unit of the TBA 1 amplifies the CATV signal to a predetermined level and branches it to the branch main line 3 and outputs the CATV signal to the subsequent main line 2. However, although only the branch trunk line 3 branched by the TBA 1 is shown in this figure, each TB
A plurality of branch trunks are branched from A1.

A plurality of branching devices 4 connected in cascade to the branch trunk line 3, an extension amplifier (EA) 6 for amplifying a CATV signal, and a plurality of branching devices 4 following the extension amplifier 6 and the extension amplifiers. A CATV level adjuster 5 is provided in front of 6. The CATV level adjuster 5 adjusts the frequency characteristic of a signal input to the extension amplifier 5 to be flat and adjusts the level to a prescribed level by setting the frequency characteristic to a predetermined slope. . Further, the CATV signal branched by the plurality of branching units 4 is input to the receiver of each subscriber.
The extension amplifier 5 amplifies the CATV signal so that it has a predetermined level.

Next, the CATV level adjuster 5 of the present invention.
The block diagram of FIG. 2 is shown in FIG. 2, and the level adjuster 5 will be described with reference to this figure. In FIG. 2, reference numeral 11 denotes a first slope tilt circuit in which the pass loss is fixed at a low frequency f1 of the transmission band and the slope of the frequency characteristic over the entire transmission band can be continuously changed from the upper right to the lower right. Further, 12 is the frequency f2 in the high band of the transmission band.
Is a second slope tilt circuit in which the passage loss is fixed, and the slope of the frequency characteristic over the entire transmission band can be continuously changed from the upper left to the lower left, and 13 is the first slope tilt circuit.
Slope tilt circuit 11 and second slope tilt circuit 12
Select either input terminal 14 and output terminal 1
5 is a slide switch connected to the switch 5.

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 transferred to the contact b.
Is input to the first slope tilt circuit 11 via
The slope of the frequency characteristic of the slope tilt circuit 11 is CATV.
Will be given to the signal. Then, 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, a monitor circuit is connected to the monitor terminal 16 connected to the output line via the capacitor C13 to adjust the frequency characteristic of the first slope tilt circuit 11 while monitoring the frequency characteristic.

Next, when the slide switch 13 is switched to connect the contact point a and the contact point c and the contact point d and the contact point f to select the second slope tilt circuit 12, the CATV signal is output. Is input to the second slope tilt circuit 12 via the contact point c, and 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 changed so that the frequency characteristic of the CATV signal becomes flat. This time,
A monitor circuit is connected to the monitor terminal 16 connected to the output line via the capacitor C13 to adjust the frequency characteristic of the second slope tilt circuit 12 while monitoring the frequency characteristic. The second slope tilt circuit 12 is different from the first slope tilt circuit 11 in that it has a high frequency f.
Since the passage loss in 2 is fixed, different levels of 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, showing a first inductor L1 connected between the input terminal 21 and the output terminal 22, and a first resistor R1 connected in parallel with the inductor L1. , 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 a variable resistor terminal of the variable resistor R3, and this capacitor C1. A second resistor R2 connected in parallel to the input terminal 21, a second capacitor C2 connected between the input terminal 21 and ground, and a connection point between the input terminal 21, the variable resistor R3, and the fourth resistor R4. And an inductor L2 connected between the two.

The frequency characteristic of the first slope tilt circuit 11 is shown in FIG. As shown in this figure, the variable resistor R3
By sliding the variable resistance terminal of No. 2 to change its resistance value, centering on the flat frequency characteristic shown in a,
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 characteristic of the frequency axis of the signal applied to the input terminal 21, the frequency characteristic of the signal can be adjusted to be flat.

The loss amount of the flat characteristic a and the variable amount of the inclination characteristic shown by b and c are set 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 as the loss amount of the flat characteristic a increases, and conversely the variable range decreases when the loss amount of the flat characteristic a decreases. The range can be reduced. Further, the second capacitor C2 can increase the amount of attenuation of the frequency signal above the high frequency (f2) in the transmission band. In this example, the frequency f1 in the low band of the transmission band is 70 MHz,
Although the high frequency f2 is set to 300 MHz, it is not limited to this and can be a desired transmission band.

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

FIG. 6 shows the frequency characteristic of the second slope tilt circuit 12 thus constructed. As shown in this figure, the variable resistance terminal of the variable resistor R7 is slid to vary its resistance value to fix the pass loss in the high band of the transmission band around the flat frequency characteristic shown in a. The pass loss in the low band of the transmission band can be continuously changed in the vertical direction as shown in FIG. Therefore,
By adjusting the variable resistor R7 in accordance with the inclination characteristic on the frequency axis of the signal input to the input terminal 31, the frequency characteristic of the signal can be adjusted to be flat.

The loss amount of the flat characteristic a and the variable amount of the inclination characteristic shown by b and c are set in 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 also increases if the loss amount of the flat characteristic a is increased, and conversely if the loss amount of the flat characteristic a is decreased. The range can be reduced. Further, the fourth inductor L4 can increase the amount of attenuation of the frequency signal below the low frequency (f1) of the transmission band as shown in the figure. In this example, the frequency f1 in the low band of the transmission band is
Is set to 70 MHz and the high frequency f2 is set to 300 MHz, but 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 used as a reference, the first slope tilt circuit is used. Select 11,
The level and frequency characteristics of the CATV signal can be adjusted by adjusting the attenuation amount of the flat characteristic to the attenuation amount that should attenuate the CATV signal and then adjusting the variable resistor R3 so that the frequency characteristic of the CATV signal becomes flat. it can. In addition, when the amount of attenuation to be attenuated at the high frequency f2 is used as a standard, the second slope tilt circuit 12 is selected,
The level and frequency characteristic of the CATV signal can be adjusted by adjusting the attenuation amount of the flat characteristic to the attenuation amount that should attenuate the CATV signal and then adjusting the variable resistor R7 so that the frequency characteristic of the CATV signal becomes flat. it can.

[0029]

Since the present invention is configured as described above, the inclination of the selected first slope tilt circuit and the second slope tilt circuit can be determined by the right slope characteristic of the level adjuster in the first slope tilt circuit. It is possible to change continuously from rising frequency characteristics to falling right frequency characteristics, and in the second slope tilt circuit, continuously change the frequency characteristics of the entire level adjuster from rising left frequency characteristics to falling left frequency characteristics. can do. In addition, the level can be adjusted by adjusting the attenuation amount. Therefore, 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 desired frequency characteristic of a specified level.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a block diagram of a level adjuster of 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 an amplifier.

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

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

FIG. 12 is a diagram showing an aspect of adjusting frequency characteristics.

FIG. 13 is a diagram showing an aspect of adjusting frequency characteristics.

[Explanation of symbols]

 1,101 Main line branch amplifier 2,102 Main line 3,103 Branch main line 4,104 Branch device 5 Level adjuster 6,105 Extension amplifier 11 First slope tilt circuit 12 Second slope tilt circuit 13 Slide switch 14, 21, 31 Input Terminals 15, 22, 32 Output terminals 16 Monitor terminals 201-1 to 201-4 BON circuits R1 to R8 Resistors C1 to C4, C11 to C13 Capacitors L1 to L4 Inductors

Claims (2)

[Claims] 1. An input terminal and an output terminal, a first slope tilt circuit in which a pass loss in a low 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 varied, and a high band of the transmission band. A second slope tilt circuit that has a fixed pass loss and that can change the slope of the frequency characteristic of the pass loss in the entire transmission band; and a slope tilt circuit of either the first slope tilt circuit or the second slope tilt circuit. A level adjuster for CATV, comprising a switching means which is selectively connected between the input terminal and the output terminal. 2. The level adjuster for CATV according to claim 1, wherein a monitor terminal is connectable to a line connected to the output terminal.