JP2585203B2 - Transmission line characteristic measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission line characteristic measuring device for measuring transmission line characteristics of a radio line and a wired system.
More specifically, the present invention relates to a transmission line characteristic measuring device for measuring transmission line characteristics for CATV, high-definition television, information communication systems, and the like.

[0002]

2. Description of the Related Art As a conventional transmission line characteristic measuring apparatus, a closed circuit is formed between a measuring apparatus 9a such as a network analyzer and a device under test 10 as shown in FIG. While transmitting, the signal transmitted from the device under test is received, and the transmission line characteristics are measured based on the change in the signal.

However, when measuring transmission path characteristics of a large-scale system such as CATV, several km to several tens km are required.
Alternatively, it is practically impossible to form such a closed circuit for a transmission line having more transmission lines. In addition, satellite broadcasting has been developed as such high-quality video broadcasting, and it has become necessary to measure transmission path characteristics in such a satellite broadcasting system.

[0004]

In order to solve such a problem, various types of measuring devices in which a transmitting device and a receiving device for measuring signals are separated from each other have been developed as measuring devices for measuring transmission characteristics in an open circuit. However, there is only one communication channel that can be measured at a time, and the measurement accuracy is low, so the performance is not sufficient to measure the characteristics of the transmission path for high-quality video broadcasting and information communication. CAT
There has not yet been a measuring device capable of efficiently measuring the characteristics of a transmission path such as a V system, a high-definition television system, and a satellite broadcasting system.

[0005] The present invention has been made in view of such a point,
The purpose is to measure the transmission characteristics of the device under test without forming a closed circuit, and also to be able to handle a large number of channels with high accuracy and to measure the transmission line efficiently. It is to provide a measuring device.

[0006]

SUMMARY OF THE INVENTION The present invention is to solve the above problems, first or second transmission frequency f _A, the timing generating section 14 to select the f _B, the first or the second transmission frequency an FM modulator 11 that performs FM modulation by f _A and f _B to generate a carrier f ₀ having a predetermined frequency, a local oscillator 13 that changes the oscillation frequency in steps of predetermined frequency steps, mixing section 1 for synthesizing a measurement signal f ₀ + f ₁ ~f _n by mixing the bandwidth setting signal f ₁ ~f _n supplied with carrier f ₀ from the local oscillation section 13
2, a control unit 15 for controlling these operations, and a display unit 16 connected to the control unit 15 for inputting and outputting information.
And an input unit 17. The control unit 15 changes the oscillation frequency of the local oscillation unit 13 in accordance with the frequency bandwidth of the device under test using the first transmission frequency f _A , and the measurement signal f ₀ + F _{1 to} f _n , and at this time, the transmitting device 1 that synchronizes with the receiving device 2 using the second transmission frequency f _B , and the frequency component of the carrier f ₀ according to an instruction from the control unit 32. A local oscillation unit 27 that oscillates a frequency corresponding to the difference between the frequency components corresponding to the band setting signals f _{1 to} f _n in a stepwise manner, and a measurement signal f ₀ + f _{1 to} f _n received from the local oscillation unit. A mixing unit 22 that mixes the signals f ₀ -f _{1 to} f _n to generate a signal under test f ₀ ′ having a predetermined frequency, and an amplitude data extraction unit 36 that extracts amplitude data from the obtained signal under test f ₀ ′. And FM detection of the signal from the mixing unit 22 to perform the first
Or FM for extracting the second transmission frequency components f _A and f _B
The detection unit 23 and the obtained first transmission frequency components f _A , f
A phase data extraction unit 37 for extracting phase data from _B ;
A timing generator 29 for generating a timing signal for receiving the resulting second transmit frequency component f signal to be measured from the _B, the amplitude data, the control unit that receives the measurement data, such as phase data to control them 32, a display unit 34 and an input unit 33 connected to the control unit 32 for inputting and outputting information, and a communication unit 35 for connecting the external analysis computer 3 and the control unit 32. ,
It synchronizes the reception timing of the measurement signal f ₀ + f ₁ ~f _n by receiving the second transmission frequency f _B, which is transmitted from the transmitting apparatus 1, depending on the frequency of the measurement signal f ₀ + f ₁ ~f _n The frequency of the signal under test f ₀ ′ is kept constant by changing the oscillation frequency of the local oscillation unit 27, and the obtained measurement data such as amplitude data and phase data is transmitted to the communication unit 3.
Receiving device 2 for sending to analysis computer 3 via computer 5
It was decided to be constituted by.

[0007] The measurement data includes an FM detector 23.
Differential gain data obtained via differential gain data extraction unit 39 from the first transmission frequency component f _A obtained from was also comprise.

[0008]

A carrier signal is FM-modulated at a transmission frequency of a predetermined frequency to obtain a measurement signal for measuring the transmission characteristics of a transmission line. At this time, a signal having a frequency corresponding to the channel of the transmission line is oscillated from the local oscillator 12 separately from the measurement signal, and this signal is superimposed on the carrier wave as a band setting signal to form a measurement signal. The transmission characteristic of the transmission line having the above can be continuously measured by one measuring device.

Further, in order to receive the measurement signal transmitted at that time, it is necessary for the receiving device 2 to synchronize with the transmission timing of the transmitting device 1. Therefore, two types of the transmission frequencies are prepared, the first transmission frequency is a transmission frequency for superimposing a band setting signal to form a measurement signal, and the second transmission frequency is a transmission frequency between the transmission device 1 and the reception device 2. The transmitting device 1 transmits a second transmission frequency for a certain period of time by the timing generator 14 when transmitting the measurement signal, and the timing generator 29 of the receiving device 2 transmits the second transmission frequency. By detecting the second transmission frequency, it becomes possible to take timing for receiving the measurement signal transmitted thereafter.

Further, the receiving apparatus 2 receives the measurement signal transmitted in accordance with the channel set on the transmission path, and oscillates a signal having a frequency of a difference between the band setting signal for channel setting and the carrier from the local oscillator 27. By superimposing this signal on the measurement signal, a measurement signal composed of various frequencies is set as a signal to be measured having a constant frequency by channel setting, and the subsequent processing is performed.
A circuit configuration corresponding to only a certain frequency is sufficient, and the signal under measurement can be efficiently and accurately processed.

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings. 1 to 4 are block diagrams showing a configuration of a measuring apparatus according to an embodiment of the present invention. FIG. 1 is a block diagram showing a principle of a transmitting apparatus according to the present invention. FIG. 3 shows a detailed configuration thereof. FIG. 2 is a block diagram showing the principle of the receiving apparatus according to the present invention, and FIG. 4 is a block diagram showing the detailed configuration thereof.

1 and 3, reference numeral 1 denotes a transmitting device, 11 denotes an FM modulator, and an FM modulator 42 for applying FM modulation to a predetermined carrier using a first transmission frequency oscillated by an OSC 41, and stabilizing this frequency. The output of the FM modulator 42 is input and a predetermined output is applied to the FM modulator 42. The APC 43 and the attenuation rate is adjusted based on the signal input from the output terminal 18 via the amplifier 51 and the AM detector 52. And the AGC 44. In addition, the OS
C41 is connected to the FM modulator 42 by a changeover switch, and is switched to the OSC 14 as a timing generation unit by a signal from the control unit 15 as necessary, and the second transmission frequency is supplied to the FM modulator 42. It has become so.

The carrier f ₀ transmitted from the FM modulator 11
After the unnecessary frequency components are removed through the bandpass filter 45 and the amplifier 46 and adjusted to a signal of a predetermined level, the signal is input to the mixing unit 12, and the mixing unit 12 is connected to the control unit 15. The output of the local oscillation unit 13 composed of the PLL 50 and the VCO 49 that oscillates upon receiving the output of the PLL 50 is input. The local oscillator 13 transmits the band setting signals f _{1 to} f _n by changing the oscillation frequency stepwise according to the setting channel of the transmission path to be measured in accordance with an instruction from the controller 15. The setting signals f _{1 to} f _n are superimposed on the carrier f ₀ by the mixing unit 12 and sequentially transmitted from the output terminal 18 as individual measurement signals f ₀ + f _{1 to} f _n corresponding to each channel of the transmission path to be measured. .

The control unit 15 controls the transmission operation and the like of the transmission device in accordance with a predetermined program, and comprises a CPU, a storage element such as a ROM and a RAM connected to the CPU, and other peripheral parts. , The display unit 16
And the input unit 17 are connected. The display unit 16 displays necessary information such as data input to the control unit 15 and a control procedure. In this embodiment, an LED display is used. The input unit 17 inputs the oscillation frequency of the local oscillation unit 13, the transmission procedure of the measurement signals f ₀ + f _{1 to} f _n , and other necessary data in accordance with the above-described transmission channel setting channel. You are using a keyboard.

In FIGS. 2 and 4, reference numeral 2 denotes a receiving device. The measuring signal input through an input terminal 38 is adjusted to a predetermined level by an attenuator 40 to remove unnecessary high-frequency components. The output of the AM detector of the amplitude data extractor, which will be described later, is input to the AGC 61 that automatically adjusts the attenuation so that the signal level becomes constant through the filter 21, and is further input to the mixer 22. Have been.

A signal from a local oscillator 27 composed of a PLL 69 connected to the controller 32 and a VCO 70 oscillating upon receiving the output of the PLL 69 is input to the mixer 22. This local oscillation unit 27 includes the control unit 3
2, the oscillation frequency is changed stepwise according to the set channel of the transmission path to be measured, and the individual measurement signals f ₀ + f ₁ corresponding to each channel of the transmission path to be measured.
Oscillates a signal f ₀ −f _{1 to} f _n having a frequency of a difference between the band setting signals f _{1 to} f _n and the carrier f _0, which are set so as to be f _n −f _n. Are mixed and output as a signal under test f ₀ ′ having a predetermined frequency.

The control section 32 controls the receiving operation of the receiving apparatus 2 and the like, and has the same configuration as the control section 15 of the transmitting apparatus 1. The input unit 33 and the display unit 34 connected to the control unit 32 correspond to the above-described measurement signals f ₀ + f _{1 to} f _n from the transmission device 1 and receive a frequency channel or a reception procedure. And the like, and the input data and other necessary information are displayed. The configuration is almost the same as that of the transmission device 1.

Further, the control unit 32 is connected to communication means 35 for communication with the analysis computer 3 which is connected to the outside, and this communication means 35 uses an interface for serial communication in this embodiment. , Parallel communication or the like. In this case, the analysis computer 3 is a general personal computer system. The measurement data transmitted from the control unit 32 by the communication unit 35 by the predetermined analysis software by the communication unit 35 is used for analysis means such as FFT analysis. By using them, an amplitude frequency characteristic, a group delay frequency characteristic, a distance between a reflected wave delay time and a generation point, a reflected wave D / U ratio, and the like, which are transfer characteristics of a transmission path, are calculated.

The signal under test f output from the mixing section 22
₀ ′ is amplified to a predetermined level by an amplifier 63 after unnecessary frequency components are removed by a bandpass filter 62,
The signal is input to the FM detector 23 and the amplitude data extractor 36.
The amplitude data extraction unit 36 amplifies the signal under test f ₀ ′ to a predetermined level by the amplifier 64 of the AM detection unit 25, performs AM detection with the AM detector 65, extracts the amplitude component, and then performs a low-pass filter. Remove unnecessary high frequency components at 79,
After being amplified to a predetermined level by the amplifier 80 of the A / D converter 28, the A / D converter 81 performs A / D conversion.
The obtained amplitude data is sent to the control unit 32.

The output of the AM detector 25 is input to a level meter 56 and the above-mentioned AGC 61, so that the signal level of the signal under test f ₀ ′ input by the level meter 56 can be visually checked. I have.

The FM detector 23 adjusts the signal under test f ₀ ′ to a predetermined amplitude level or less by a limiter 67,
FM detection is performed by the detector 68, and the transmission frequency components f _A ^′ , f
Extract _B '.

The transmission frequency components f _A ^′ and f _B ′ obtained are converted by a band-pass filter 71 into first transmission frequency components f _A ^′.
Are input to the phase data extraction unit 37. The limiter 72 in the phase detector 24 of the phase data extractor 37
After being adjusted to a predetermined amplitude level by the phase detector 73
, And is subjected to phase detection to output a phase difference from the reference signal. Then, after unnecessary high-frequency components are removed by the low-pass filter 74, the signal is input to the A / D converter 30 as a phase output. Further, a part of the output of the low-pass filter is input to the VCO 76 after being amplified by the amplifier 75, and the signal oscillated by the VCO 76 is input to the phase detector 73 as a reference signal.

In the A / D converter 30, the phase output is amplified to a predetermined level by an amplifier 77, A / D converted by an A / D converter 78, and the obtained phase data is sent to a controller 32. .

The transmission frequency components f _A ^′ , f _B ′
Of the second transmission frequency component f _B ′
9 and sent to the control unit 32 as a predetermined timing signal. Although this timing generator 29 is omitted in FIG. 4, the second transmission frequency component f _B ′
And a signal converting means by a well-known method, and has an operation of detecting the transmission frequency component f _B ′ and converting it into a predetermined digital signal.

Further, a part of the first transmission frequency component f _A ^′ selected by the band pass filter 71 is amplified to a predetermined level by an amplifier 82 in the AM detector 26,
After being subjected to AM detection by the AM detector 83 to extract distortion components such as harmonic distortion, unnecessary low-frequency components are removed by the low-pass filter 84, and then input to the A / D converter 31. The A / D converter 31 outputs the differential gain output to the amplifier 8
5, and is amplified to a predetermined level by the A / D converter 86.
A / D conversion is performed, and the obtained differential gain data is sent to the control unit 32.

Next, the operation of the measuring apparatus having such a configuration will be described. FIG. 6 shows an example of a configuration for measuring transmission path characteristics of a CATV (cable television) network using the measuring apparatus according to the present invention.

In the figure, reference numeral 4 denotes a television signal processor for receiving television signals of respective channels, adjusting the levels of image signals and audio signals, and synthesizing signals, and 5 denotes a signal from each television signal processor 4 on a transmission line. , A mixer for maintaining the signal on the transmission line at a predetermined level, and a divider 7 for distributing the signal to each terminal.

Then, the transmitting apparatus 1 is connected to a mixer 5 to which a plurality of television signal processors 4 in a broadcasting station called a head end are connected, and the mixer 5 is connected to one of the distributors 7 on the terminal side of the transmission path to be measured. Connect the receiving device.

For example, if there are 1 to 60 channels used in the CATV network to be measured, the number and frequency of the channels or the channels not to be measured are provided from the input units 16 and 33 of the transmitter 1 and the receiver 2. In this case, an instruction to skip that part is input.

The control unit 15 of the transmitting device 1 performs the first to the 60th channel on the basis of the input data.
The oscillation frequency of the local oscillation unit 13 is sequentially stepped up at regular intervals in order to transmit a measurement signal using the transmission frequency f _A of.

In the receiving apparatus 2 as well, the control section 32 sequentially steps down the oscillation frequency of the local oscillation section 27 in order to receive measurement signals of channels 1 to 60 based on the input data.

At this time, in order to synchronize the transmitting apparatus 1 and the receiving apparatus 2, the measurement signals f ₀ + f _{1 to} f ₁ for each channel are set.
before sending _n, and sends the predetermined time (ta) a second transmission frequency f _B as the transmission frequency from the transmitter 1. Then, after a lapse of a predetermined time (tb), measurement signals f ₀ + f _{1 to} f _n for each channel are transmitted.

After detecting the second transmission frequency f _B , the receiving apparatus 2 starts receiving the measurement signal of each channel after a lapse of a predetermined time (tc) after switching to the first transmission frequency f _A.

FIG. 5 shows the transmission / reception timing. In the figure, (a) shows the timing of the transmitting device 1, and (b) shows the timing of the receiving device. In this way, the transmission device and the reception device 2 can be synchronized by using the first or second transmission frequency properly.

The receiving apparatus 2 changes the oscillation frequency of the local oscillation section 27 in accordance with the frequency of the measurement signal transmitted from the transmission apparatus 1 so that the received measurement signal and the local oscillation section 2
Since the frequency of the signal under measurement synthesized with the signal from the signal 7 is kept constant, the sensitivity and accuracy of the receiving circuit can be easily adjusted by always using a single frequency signal. It can be measured with high accuracy even with a low-cost device.

It should be noted that if the transmitter 1 and the receiver 2 are connected in a through manner before measurement, and both the devices 1 and 2 are calibrated by performing transmission and reception, the best results are obtained without being affected by the environment or aging. Measurement accuracy can be maintained.

Next, an example of the appearance of the apparatus according to the present invention will be described with reference to the drawings. FIGS. 7A and 7B are external views of the transmitting device 1, wherein FIG. 7A is a front view and FIG. 8B is a rear view, and FIG. 8 is an external view of the receiving device, FIG. 7A is a front view, and FIG. .

In the figure, reference numerals 1a and 2a denote main bodies of a transmitting device or a receiving device, 101 and 111 denote power switches, 1
02, 112 are AUT switches for automatic measurement,
Reference numerals 103 and 113 denote RUN switches for starting measurement, and reference numerals 16a and 34a denote displays constituting the display units 16 and 34, which are constituted by 7-segment LEDs or the like. 1
Numerals 7a and 33a denote keyholes constituting the input sections 17 and 33, and 16-point keys are used.

Reference numerals 40a and 44a are used for adjusting the output or input level by an attenuator. 66a constitutes the level meter 56, which is of an analog type here, but may be of a digital type using an LED or the like.

Reference numerals 104 and 114 denote ground terminals, 18a an output terminal, 38a an input terminal, 105 and 115 fuses, and 106 and 116 power connectors.

As described above, the transmitting device 1 and the receiving device 2 both have a compact structure, and are easy to carry and install when measuring various transmission paths.

[0042]

As described above, according to the present invention, since the transmitting device and the receiving device are synchronized by using the first or second transmission frequency f _A or f _B properly, a closed circuit is formed. Without this, it is possible to measure transmission paths, and it is possible to measure transmission paths in long-distance transmission systems and satellite broadcasting systems.

Further, the transmitting device has a local oscillator, and the frequency of the measurement signal is changed stepwise by the local oscillator, and the local oscillator of the receiving device is changed according to the frequency of the measurement signal transmitted from the transmitting device. Since the frequency of the section is changed and only a signal of a single frequency is handled, measurement of a transmission line having a plurality of channels can be performed easily and efficiently, and highly accurate measurement can be performed with a device having a relatively simple configuration. Is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the principle of a transmission device according to the present invention.

FIG. 2 is a block diagram showing a detailed configuration of the transmission device of FIG.

FIG. 3 is a block diagram showing the principle of a receiving device according to the present invention.

FIG. 4 is a block diagram showing a detailed configuration of the receiving device of FIG. 2;

5A and 5B are diagrams illustrating timings of operations of a transmission device and a reception device, wherein FIG. 5A illustrates operations of the transmission device, and FIG. 5B illustrates timings of operations of the reception device.

FIG. 6 is a diagram showing an example of a configuration for measuring the characteristics of a CATV network using the measuring device according to the present invention.

FIGS. 7A and 7B are views showing an example of the appearance of the transmission device 1 according to the present invention, wherein FIG. 7A is a front view, and FIG.

FIGS. 8A and 8B are diagrams showing an example of the external appearance of the receiving apparatus 1 according to the present invention, wherein FIG. 8A is a front view and FIG. 8B is a rear view.

FIG. 9 is a diagram showing an example of transmission line measurement by a conventional measurement device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transmitter 2 receiver 3 analysis computer 4 television signal processor 5 mixer 6 amplifier 7 distributor 11 FM modulator 12 mixer 13 local oscillator 14 timing generator 15 controller 16 display unit 17 input unit 18 output terminal 21 filter Unit 22 mixing unit 23 FM detection unit 24 phase detection unit 25 AM detection unit 26 AM detection unit 27 local oscillation unit 28 A / D conversion unit 29 timing generation unit 30 A / D conversion unit 31 A / D conversion unit 32 control unit 33 Input unit 34 Display unit 35 Communication means 36 Amplitude data extraction unit 37 Phase data extraction unit 38 Output terminal 39 Differential gain data extraction unit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Minoru Honda, 2-2-1 Jinnan, Shibuya-ku, Tokyo Japan Broadcasting Corporation Broadcasting Center (72) Toshihiro Kubo 2-2-1 Jinnan, Shibuya-ku, Tokyo Japan Broadcasting Corporation Broadcasting Center (56) References JP-A-52-123116 (JP, A) JP-A-6-284451 (JP, A)

Claims (2)

(57) [Claims] A timing generator for selecting a first or second transmission frequency; an FM modulator for performing FM modulation with the first or second transmission frequency to generate a carrier having a predetermined frequency; A local oscillating unit that changes the oscillation frequency stepwise in frequency steps, a mixing unit that combines a carrier wave of the predetermined frequency and a band setting signal supplied from the local oscillating unit to synthesize a measurement signal, A control unit for controlling the operation, a display unit connected to the control unit for inputting and outputting information, and an input unit, wherein the control unit controls the first transmission frequency according to the frequency bandwidth of the device under test. A transmitting device that changes the oscillation frequency of the local oscillation unit according to an instruction from the unit, transmits a measurement signal, and synchronizes with the receiving device using the second transmission frequency at that time, and according to an instruction from the control unit. Said carrying A local oscillation unit that oscillates a frequency corresponding to a difference between a frequency component of a wave and a frequency component corresponding to the band setting signal in a stepwise manner, and mixes a received measurement signal and a signal from the local oscillation unit with a predetermined frequency. , An amplitude data extractor for extracting amplitude data from the obtained signal to be measured, and FM detection of the signal from the mixer to extract the first or second transmission frequency component. An FM detector, a phase data extractor for extracting phase data from the obtained first transmission frequency component, and a timing for generating a timing signal for receiving the signal under measurement from the obtained second transmission frequency component A generation unit, a control unit that controls these and receives the measurement data such as the amplitude data and the phase data, a display unit and an input unit connected to the control unit for inputting and outputting information, and an external unit. A communication unit for connecting the analysis computer and the control unit; receiving the second transmission frequency transmitted from the transmission device to synchronize the reception timing of the measurement signal; A receiving device that keeps the frequency of the signal under measurement constant by changing the oscillation frequency of the local oscillation unit in accordance with the frequency, and sends the obtained measurement data such as amplitude data and phase data to an analysis computer via communication means. And a transmission line characteristic measuring device. 2. The measurement data according to claim 1, wherein the measurement data includes differential gain data obtained through a differential gain data extraction unit from a first transmission frequency component obtained from an FM detection unit. Transmission line characteristic measuring device.