JPH0511686B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a trunk line equalizer that can obtain good equalization characteristics with simple adjustment, and a method of using the same.

(Conventional technology) Conventionally, radio, television broadcasting, etc.
NTT telephone lines are used as trunk lines for wideband voice transmission. The transmission frequency characteristics of trunk lines are such that attenuation increases as the frequency increases, and
The longer the transmission distance, the greater the overall loss.

In order to create and equalize an inverse frequency characteristic that matches the attenuation frequency characteristic of such a relay line, conventionally a 2-terminal equalizer, a 4-terminal equalizer, an equalizing amplifier, a combination thereof, or a graphic equalizer has been used. I was using it.

The 2-terminal and 4-terminal equalizers combined a coil L, capacitor C, and resistor R to form a resonant circuit as shown in Figure 2, and set the resonant frequency to the limit frequency for high frequency correction, for example 10kHz. . Actual equalization is performed by changing the inductance of the coil L, the capacitance of the capacitor C, and the resistance value of the resistor R.
This was done by changing the amount of equalization and the amount of equalization to create an inverse characteristic of the frequency characteristics of the relay line.

In addition, in long-distance transmission systems, wideband transmission systems, etc., bump equalizers having several equalization sections connected in series are used, as shown in Japanese Patent Application Laid-Open No. 48-98708. ing.

The bump equalizer is composed of a plurality of independent equalization units that employ equalization methods similar to the above-mentioned graphical equalizer.
Each equalization unit corresponds to a plurality of equalization sections obtained by dividing one transmission band, and can perform equalization within each amplitude range and narrow frequency range.

(Problems to be Solved by the Invention) In order to set the above characteristics, it is first necessary to measure the bare characteristics of the trunk line. Then, based on this data, measure the frequency, for example 1kHz, 5kHz, 8kHz.
The constants of the resonant circuit are changed as shown in FIG. 3 so that the equalizer output becomes flat at the three points, and an inverse characteristic of high-frequency attenuation is obtained.

However, this adjustment requires skill and time, and there are problems in that it is often difficult to obtain satisfactory equalization characteristics.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a trunk equalizer that eliminates the above-mentioned problems and provides good equalization characteristics with simple adjustment, and a method for using the same.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention uses a trunk equalizer that equalizes a single equalization section to reduce the loss in the low frequencies of the trunk. A wideband amplifier with adjustable gain for compensation and a time constant for the lower part of the equalization band of the trunk line.
A first high-frequency emphasizing amplifier with adjustable T1 and a time constant for the mid-range portion of the equalization band of the relay line.
a second high-frequency emphasizing amplifier as a characteristic complement of the time constant T1, which is adjustable in T2; Equipped with a third high-frequency emphasizing amplifier to complement the characteristics of T2, and a low-pass filter with an adjustable cutoff frequency to remove the emphasized noise components outside the equalization interval, these are expressed as follows: are connected in cascade in the order of T1>T2>T3 between each of the above time constants.
When using a trunk line equalizer characterized by the following relationship being established, a signal generator is connected to the transmitting end of the trunk line, and a trunk line equalizer is connected to the receiving end of the trunk line. and further connect a level measuring device to the output terminal of the trunk line equalizer,
A predetermined low frequency signal F1 is sent out from the signal generator at a specified sending level, and the gain of the wideband amplifier is adjusted to compensate for the transmission loss of the trunk line so that the detection level at this time becomes the predetermined equalization reference level. 1 in the low frequency range of the transmission band of the trunk line from the signal generator.
Send out two sine wave signals F2 at the specified sending level,
In order to make the detection level at this time equal to the equalization reference level, the time constant T1 of the first high-frequency emphasizing amplifier is adjusted so that the high-frequency emphasizing curve with a constant slope is moved from the higher frequency side to the lower frequency axis on the frequency axis. Then, the signal generator sends out one sine wave signal F3 within the middle range of the transmission band of the trunk line at the specified sending level, and the detection level at this time becomes the equalization reference level. So, the time constant T2 of the second high-frequency emphasis amplifier
is adjusted by moving a high-frequency emphasis curve with a constant slope in parallel on the frequency axis from high to low frequencies to complement the characteristics of the time constant T1, and then adjust the transmission band of the relay line from the signal generator. One sine wave signal F4 within the high range of is sent out at the specified sending level, so that the detection level at this time becomes the equalization reference level.
The time constant T3 of the third high-frequency emphasizing amplifier is changed to the time constant T1
To complement the characteristics of T2, adjust the high-frequency emphasis curve with a constant slope by moving it in parallel on the frequency axis from high to low frequencies, and then terminate the transmitting end of the relay line with a predetermined resistance value. , the SN obtained from the detection level at this time and the equalization reference level
The low-pass filter is cut off so that the ratio reaches the standard value required for operation in advance, and in order to widen the frequency band as much as possible by removing unnecessary noise components outside the band emphasized by the high-frequency boost amplifier. Now you can set the frequency.

(Function) According to the trunk line equalizer of the present invention, the signal level at the receiving end of the trunk line is adjusted by the wideband amplifier, and furthermore, the signal level at the receiving end of the trunk line is adjusted by the first high-frequency emphasizing amplifier, and the low frequency part of the frequency band of the trunk line is adjusted by the first high-frequency emphasizing amplifier. The second high-frequency emphasizing amplifier equalizes the mid-range portion of the relay line, the third high-frequency emphasizing amplifier equalizes the high-frequency portion of the relay line, and the low-pass filter According to the method of using the trunk line equalizer of the present invention, the noise components are blocked and the desired equalization characteristics are obtained. A desired equalization characteristic can be set by adjusting the time constant for the band emphasis amplifier and switching the cutoff frequency for the low pass filter at least five times.

(Example) First, the principle of the trunk line equalizer of the present invention will be explained.

Figure 4 shows an example of the attenuation frequency characteristics of NTT's telephone line.If we organize this data based on the 100Hz level, classify the 5kHz attenuation using a 5dB resin, and perform statistical processing for each frequency. ,
The graph shown in FIG. 5 is obtained.

In FIG. 5, the vertical axis shows the deviation and the horizontal axis shows the frequency. If one curve is selected from a group of these curves and moved in the frequency direction (left and right), all the curves can be superimposed. Therefore, the attenuation curve can be approximated by a single line, and can also be expressed by an attenuation characteristic of 6 dB/octave.

From this, by making the time constant of the 6 dB/octave high frequency emphasis time constant circuit (amplifier) variable and moving one curve in the frequency direction (left and right), the inverse characteristic of the attenuation frequency characteristic of the telephone line can be achieved. It can be seen that equalization can be achieved.

FIG. 1 shows an embodiment of the trunk line equalizer of the present invention, in which 1 is a wideband amplifier, 2 is a first high-frequency emphasizing amplifier, 3 is a second high-frequency emphasizing amplifier, and 4 is a high-frequency emphasizing amplifier.
5 is a third high-frequency emphasizing amplifier (hereinafter referred to as a first amplifier, a second amplifier, and a third amplifier, respectively), and 5 is a low-pass filter.

The wideband amplifier 1 is composed of a well-known gain-adjustable amplifier, and adjusts the voltage level of the audio signal transmitted through the trunk line to a predetermined level.

First amplifier 2 is 6dB/octave, 0~500μs
It has a variable time constant T1 range of , and mainly corrects the frequency characteristics of 1 kHz or less for the signal output from the wideband amplifier 1. The second amplifier 3 is 6dB/
It has a variable time constant T2 range of octave and 0 to 200 μs, and mainly corrects the frequency characteristics of 3 kHz or less for the signal output from the first amplifier 2. Third
The amplifier 4 has a variable time constant T3 range of 6 dB/octave and 0 to 100 μs, and mainly corrects the frequency characteristics of 7 kHz or less for the signal output from the second amplifier 3.

The low-pass filter 5 is capable of switching its cutoff frequency to several arbitrary values, for example, 10 kHz, 7 kHz, and 5 kHz, and has a signal-to-noise ratio (SN ratio) at the output of the third amplifier 4. The frequency to be cut off is changed according to the frequency, and the band is narrowed to maintain a predetermined SN ratio.

Next, a method for adjusting equalization characteristics using the present equalizer will be explained with reference to FIGS. 6 and 7.

FIG. 6 shows the connection state during measurement, in which a well-known low frequency signal generator 7 is connected to the sending end of the trunk line 6, and the input end of the trunk line equalizer mentioned above is connected to the receiving end, i.e., a broadband signal generator. The input terminal of the amplifier 1 is connected, and the level measuring device 8 is connected to the output terminal of the trunk line equalizer, that is, the output terminal of the low-pass filter 5.

Next, the adjustment operation will be described.

First, the signal generator 7 sends out a sine wave signal F1 with a frequency of 100Hz at a specified level (for example, 0dBm).
Send with . At this time, the level of the level measuring device 8 reaches a predetermined equalization reference level (for example,
Adjust the level of wideband amplifier 1 so that it becomes 0dBm). In FIG. 7, reference numeral 11 indicates the frequency characteristic of the output of the trunk line equalizer before level adjustment, and by increasing the gain of amplifier 1 by level α, the characteristic shown by reference numeral 12 can be obtained.

Next, from the signal generator 7, 1kHz from 800 to 1kHz
a sinusoidal signal F2 of one frequency (e.g. 1kHz)
is transmitted at the specified transmission level. At this time,
The time constant T1 of the first amplifier 2 is adjusted so that the level of the level measuring device 8 becomes the equalization reference level. At this time, the frequency characteristic of the first amplifier 2 becomes as shown by reference numeral 13 in FIG. 7, and the overall frequency characteristic of the output of the first amplifier 2 becomes as shown by reference numeral 14.

Subsequently, the signal generator 7 sends out a sine wave signal F3 of one frequency (for example, 3 kHz) from 2 kHz to 4 kHz at a specified sending level. At this time, the time constant T2 of the second amplifier 3 is adjusted so that the level of the level measuring device 8 becomes the equalization reference level.
Adjust. At this time, the frequency characteristic of the second amplifier 3 becomes as shown by reference numeral 15 in FIG.
The overall frequency characteristic of the output of amplifier 3 is sign 1
6.

Furthermore, the signal generator 7 sends out a sine wave signal F4 of one frequency (for example, 7 kHz) from 6 kHz to 8 kHz at a specified sending level. At this time, the time constant T3 of the third amplifier 4 is adjusted so that the level of the level measuring device 8 becomes the equalization reference level.
Adjust. At this time, the frequency characteristics of the third amplifier 4 become as shown by reference numeral 17 in FIG.
The overall frequency characteristic of the output of amplifier 4 is sign 1
8.

A desired flat frequency characteristic can be obtained by repeating the above adjustments 2 to 3 times as necessary.

Finally, terminate the transmitting end of trunk line 6 with 600Ω,
At this time, check the level of the level measuring device 8. This represents the noise level of the trunk line 6, and the SN ratio can be determined from the ratio with the equalization reference level. If this S/N ratio is lower than the S/N ratio reference value (for example, 50 db), the cutoff frequency of the low-pass wave filter 5 is sequentially switched to, for example, 7 kHz and 5 kHz, so that the transmission satisfies the S/N ratio reference value. Narrow the frequency band.

FIG. 8 shows an example of frequency characteristics when a trunk line is actually equalized. In the figure, 20 is the characteristic of the trunk line itself, 21 is the characteristic of a conventional equalizer, and 22
shows the characteristics of the trunk line equalizer of the present invention, and it can be seen that according to the present invention, flat characteristics are obtained at a high level over almost the entire frequency band.

FIGS. 9a and 9b show specific examples of circuits of the high-frequency emphasizing amplifier in the equalizer of the present invention.

In Figure 9a, OP1 is an operational amplifier, C1
is a capacitor, and R1 and R2 are resistors. Here, resistors R1 and R2 are variable resistors, and resistor R1
By changing , the time constant with the capacitor C1 is changed, and its equalization characteristic is changed. Further, at this time, the gain can be kept constant by changing the resistance R2 so as to keep the ratio with the resistance R1 constant. Gain A1 between input and output of the circuit
is as shown in the following equation.

A1=(−R2/R1)・{1+(2πC1R1) ² } ^1/2 (However, is frequency) In Figure 9b, OP2 is an operational amplifier, C2
is a capacitor, and R3 and R4 are resistors. Here, the capacitor C2 is a variable capacitor, and by changing the capacitor C2, the resistance R
3, and its equalization characteristics are changed. Note that in this case, the ratio between resistors R3 and R4 does not change, so the gain can be kept constant. The gain A2 between the input and output of the circuit is given by the following equation.

A2=(−R4/R3)·{1+(2πC2R3) ² } ^1/2 (Effects of the Invention) As explained above, the present invention has the following effects.

1. It can also handle the correction of relay lines that exhibit complex attenuation characteristics.

2. There is no need to measure the bare characteristics of the relay line, and corrections can be made immediately.

3. No skill is required for correction, and adjustment time for correction can be shortened (about 1/10th compared to conventional methods).

4. Can easily be connected to a control device for automatic correction.

5. There are no extreme peaks or valleys in the correction results, and smooth equalization can be obtained.

6. By repeating fine tuning, the deviation from 1kHz can be reduced (normally, a deviation of ±0.5dB can be easily obtained).

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure is a circuit diagram showing an example of a conventional equalizer, Figure 3 is a diagram showing the frequency characteristics of the equalizer in Figure 2, and Figure 4 is a diagram showing the frequency characteristics of the equalizer in Figure 2.
A diagram showing an example of the attenuation frequency characteristics of NTT's telephone line, FIG. 5 is a statistical processing diagram of the frequency characteristics of FIG. 4, and FIG. 6 is a connection diagram showing the state of use of the trunk line equalizer of the present invention. FIG. 7 is a diagram showing the state of equalization in each circuit, FIG. 8 is a frequency characteristic diagram showing an example of equalization, and FIGS. 9a and 9b are diagrams showing an example of a circuit of a high frequency emphasizing amplifier. 1... Wideband amplifier, 2... First high frequency emphasizing amplifier, 3... Second high frequency emphasizing amplifier, 4... Third
5...low-pass filter.

Claims (1)

[Scope of Claims] 1. A trunk line equalizer that equalizes a single equalization section, comprising: a wideband amplifier with adjustable gain for compensating for losses in low frequencies of the trunk line; a first high-frequency emphasizing amplifier capable of adjusting a time constant T1 for a low-frequency portion of the equalization band of the relay line; a second high-frequency emphasizing amplifier as a characteristic complement of the constant T1; and a third high-frequency emphasizing amplifier as a characteristic complement of the time constants T1 and T2, capable of adjusting the time constant T3 for the high-frequency portion of the equalization band of the relay line. It is equipped with a high-frequency emphasizing amplifier, and a low-pass filter whose cut-off frequency is adjustable to remove the emphasized noise components outside the equalization interval. These are connected in cascade in the order shown, and each of the above A trunk line equalizer characterized in that the relationship T1>T2>T3 holds between time constants. 2 Connect a signal generator to the transmitting end of the trunk line, connect the input terminal of the trunk line equalizer to the receiving end of the trunk line, and further connect a level measuring device to the output terminal of the trunk line equalizer. , A predetermined low frequency signal F1 is sent out from the signal generator at a specified sending level, and the gain of the wideband amplifier is adjusted to compensate for the transmission loss of the trunk line so that the detection level at this time becomes the predetermined equalization reference level. Next, one sine wave signal F2 in the low frequency band of the transmission band of the trunk line is sent out from the signal generator at the specified sending level, and the first The time constant T1 of the high-frequency emphasis amplifier is
The high-frequency emphasis curve with a constant slope is adjusted by moving parallel on the frequency axis from high to low frequencies, and then the signal generator generates one sine wave signal within the middle range of the transmission band of the trunk line. F3 is sent out at the specified sending level, and the time constant T2 of the second high-frequency emphasis amplifier is set so that the detection level at this time becomes the equalization reference level.
To complement the characteristics of the time constant T1, a high-frequency emphasis curve with a constant slope is adjusted by moving parallel on the frequency axis from high to low frequencies, and then the signal generator One sine wave signal F4 within the range is sent out at the specified sending level, and the time constant T3 of the third high frequency emphasizing amplifier is set so that the detection level at this time becomes the equalization reference level.
To complement the characteristics of time constants T1 and T2, a high-frequency emphasis curve with a constant slope is adjusted by moving parallel on the frequency axis from high to low frequencies, and the transmitting end of the relay line is adjusted to a predetermined resistance value. The terminal is terminated at a high frequency amplifier so that the SN ratio obtained from the detection level at this time and the equalization reference level reaches the reference value required for operation in advance, and unnecessary noise components outside the band emphasized by the high-frequency amplifier are removed. A method of using a trunk line equalizer, characterized in that the cut-off frequency of a low-pass filter is set so as to widen the frequency band as much as possible.