JPH01296170A - Frequency characteristic measuring method of transmission path - Google Patents

Abstract

PURPOSE:To obtain the characteristic of ripples, by AM-detecting a signal detected at a measuring terminal of a transmission path to be measured when a transmission signal is inputted to an input terminal thereby to obtain the maximum level, and adding mathematic operations to the logarithmic difference between the maximum level and a presumptive level. CONSTITUTION:For example, a BS-IF signal is preliminarily inputted in a calibrating transmission path which is different from a transmission path to be measured, and the signal is AM detected in a narrow band by frequencies at a predetermined interval. Thus, the level of the inputted transmission signal is presumed. Then, in measuring terminals 28-32 of the transmission path to be measured, the level of an outputted transmission signal is obtained through the AM detection in a narrow band by frequencies at a predetermined interval. The difference of logarithmic values between the obtained level of the transmission signal and the preliminarily presumed level is subjected to an operation by Fourier conversion etc., so that the frequency and amplitude of ripples in the transmitting frequency and amplitude characteristic in the transmission path to be measured are obtained. Accordingly, the characteristic of ripples of the transmission path can be known without interrupting signals which are being transmitted.

Description

[Detailed Description of the Invention] [Industrial Application Tn] The present invention relates to a method for measuring frequency characteristics of a transmission line, for example, B
The present invention relates to a measurement method suitable for ripple analysis of frequency amplitude characteristics in an S-IF transmission line.

[Summary of the Invention] The present invention provides a method for measuring transmission frequency characteristics of a transmission path (for example, a cable transmission path in the BS-IF band) by transmitting data to a calibration transmission path with known frequency characteristics that is separate from the transmission path under test. After inputting a signal (for example, a BS-IF signal) and performing narrowband AM detection at frequencies at regular intervals, the maximum level for each frequency of the transmission signal at the input end of the transmission line under test is estimated in advance. When the transmission signal is input, the detection signal at the measurement terminal of the transmission line under test is subjected to narrowband AM detection at the same fixed interval frequency as the former, and the maximum level of each is determined, and the logarithmic difference from the above level estimated in advance is calculated. This method calculates the ripple frequency and ripple amplitude in the transmission frequency and amplitude characteristics of the transmission line under test by performing calculations such as Fourier analysis. In this way, since measurements are performed using signals such as transmitted broadcast waves, there is no need to insert measurement signals such as sweep signals into the head end, and therefore ripples on the transmission line under test can be eliminated without interrupting the transmission line under test. You can know the characteristics.

[Prior art] Conventionally, in this type of measurement method, a sweep signal is inserted by a signal sweeper or the like at the head end of the transmission line under test, and the frequency amplitude characteristics are observed at the measurement terminal of the transmission line under test using a spectrum analyzer or the like. However, it is mainly used to analyze ripples.

Particularly when receiving satellite broadcasting, disturbances are caused to the received image due to disturbances in frequency and amplitude characteristics caused by poor connection of the cable connected to the output end of the BS converter.
In order to understand the extent of this, it is necessary to mainly pay attention to the ripple characteristics within the band for one channel of satellite broadcasting.

[Problems to be Solved by the Invention] However, in the conventional measurement method, by making the frequency and frequency bias of the sweep signal variable, it is possible to measure any frequency or frequency.
Although the frequency amplitude characteristics can be observed using the bandwidth, it is necessary to interrupt the broadcast wave and insert a sweep signal, and especially in the case of joint reception, it is impossible to receive the broadcast at all terminals on the transmission path during the measurement. .

These drawbacks are due to satellite broadcasting and joint transmission channels.
The same problem occurs when receiving HF broadcasting or other transmission signals.

Therefore, in view of the above-mentioned points, an object of the present invention is to provide a method capable of measuring frequency amplitude characteristics without interrupting the transmission path of a transmission signal.

[Means for Solving the Problems] In order to achieve the above object, the present invention uses F
To measure the frequency amplitude characteristics of a transmission signal such as an M-modulated high-frequency signal on a transmission path, the transmission signal is input for a certain period of time to a calibration transmission path having known frequency characteristics, and the transmission signal is measured at regular intervals. Narrowband AM detection is performed for each frequency to determine each maximum test level during the certain period, and by correcting each maximum test level based on the known frequency characteristics, After estimating the maximum level for each frequency of the transmission signal and storing the logarithm value of the level as comparison data, inputting the transmission signal to the transmission line under test for a period equivalent to the certain period, Narrowband AM detection is performed for each frequency at regular intervals to determine each maximum measurement level, the difference between the comparison data and the logarithm value of each maximum measurement level is determined, and Fourier transform processing is performed. This method measures the ripple frequency and ripple amplitude in the frequency and amplitude characteristics of the transmission line under test.

[Function] The present invention is applicable to the measurement of the transmission frequency characteristics of a transmission line (for example, a transmission line in the BS-IF band) of a transmission signal such as a high frequency signal that is FM modulated with an image signal. The transmission signal (
For example, after estimating each level of the input transmission signal in advance by inputting a BS-IF flaw signal and performing narrowband AM detection at frequencies at regular intervals, the output transmission signal at the measurement terminal of the transmission path under test is detected at the regular intervals. By performing narrowband AM detection at a frequency of Since the ripple amplitude can be found,
By using a transmission signal (for example, a BS-IF signal) instead of a sweep signal, it is possible to know the ripple characteristics within the channel band. Frequency amplitude characteristic measurements can be performed.

Note that the modulation method is not limited to FM as long as the measurement method according to the present invention is effective for obtaining suitable data corresponding to the above-mentioned comparison data. Furthermore, as long as the transmission signal is concerned with frequency amplitude characteristics within the transmission band, the modulation signal does not need to be limited to an image signal, and as long as the transmission path is similar, it does not need to be limited to a wired system.

[Example] Hereinafter, the present invention will be described in detail based on an example of a cable transmission path during joint reception of 85-IF flaw signals.

FIG. 1 is a wiring diagram showing the procedure to be performed prior to measuring the frequency amplitude characteristics of the transmission line under test.

In this figure, 2 is an 85 for receiving satellite broadcasting radio waves.
Antenna, 4 is a BS converter for converting BS-IF flaw signals, 6 is a coaxial cable, 8 is a power supply unit for supplying DC 15V to the BS converter in 4, IO is a narrow band A
M detector, 12 is a logarithmic converter. The measurement procedure using this diagram will be described in detail later with reference to FIGS. 3 and 4.

FIG. 2 shows a system diagram of a community reception system connected to the BS converter 4. In this figure, 20 is a BS booster (including a DC power supply for the OS converter), 22 and 24 are mixers, 26 is a distributor, 28 to 34 are terminals of the series unit, and R is a terminating resistor.

As shown in this figure, the transmission line under test in this example is
This is a path from the output end of the BS converter 4 to any terminal of the series unit.

FIG. 3 shows signal waveforms obtained at each part of FIGS. 1 and 2.

First, when the output signal of the BS converter 4 is input to the coaxial cable 6 (see FIG. 1), the signal shown in FIG. 3(a) is obtained at the B terminal via the coaxial cable 6. In addition, FIG. 3(b) shows two terminals A and 8 including the coaxial cable 6.
It can be obtained, for example, by inputting the output of a sweep oscillator to the A terminal and detecting its level at the B terminal.

The waveform shown in FIG. 3(C) is the signal waveform obtained from any of the terminals 28 to 32 of the series unit when the output end of the OS converter 4 is reconnected to the BS booster 20 (see FIG. 2). It is.

Figure 4 shows the measurement procedure.
Before performing this, preliminary work (step SO) is required to generate comparison data and store it in a memory or the like. When analyzing the frequency amplitude characteristics, as will be explained in detail later, the difference between the data (logarithmic value) obtained from the broadcast wave transmitted to the transmission line under test and the comparison data (logarithmic value) is determined, and a series of By performing numerical analysis, the ripple characteristics are determined and the results are output.

Here, the frequency range to be measured is a bandwidth of 25 MI (about z) with a good CN ratio out of 27 MHz for one channel. Although it affects the resolution of the components, the bandwidth can be increased by 25%.
If it is n-30 or more in MHz, it will be practical for analysis of ripples that cause interference.

Prior to actual measurement, the following preliminary work is required.

First, make the connections shown in Figure 1, and detect the broadcast wave in a narrow band (300kHz = IMI (approximately z)) 3M at the B terminal.
The logarithm value x, + (+-0 to n-1) of the maximum value within a certain period of time (for example, 5 to 6 seconds) is stored. A constant frequency interval between samples is determined by the number of samples within the 25 MHz band to be measured, and the frequency f I (i-0 to n-1) at the sampling points of this constant frequency interval is the frequency to be detected (the (See Figure 3(a)).

Further, the frequency amplitude characteristic between the AB terminals is measured as described above, and the voltage logarithm x,'' (i-0 to n-1) at fI (i-0 to low 1) is measured. Figure 3 (
a).

(b).

Next, X-41-x, 'x1'' for fl is obtained and stored in a memory or the like as data for comparison.The operations so far are the preliminary work (step S) shown in FIG.

Here, we know from experience that if r is measured using the same procedure, it will be a constant value regardless of the measurement time, so this preliminary work is! You only need to do this once per channel.

Next, the actual measurement procedure will be explained. When measuring the characteristics of the transmission line under test shown in FIG. 2, assuming that broadcast waves as shown in FIG. 3(c) are obtained at the measurement terminals 28 to 32, f, (i-0 to n- 1) Narrow band (approximately 300 kHz to IMHz) AM detection is performed at the frequency of 1), and the logarithm xl of the maximum value within a certain period of time (e.g., 5 to 6 seconds) is detected.
"' (i-0~n-1). Here, x1"'
is unrelated to the time of measurement if it is measured using the same procedure as I .

Next, xl ``Xl''' - xl (41), which is the difference between , (<), x, and IH in fl, is obtained (step s+), and the Kono m loss data x becomes data for ripple analysis of the M frequency amplitude characteristic.

Thereafter, using a well-known numerical analysis method, first the column number data Xi
(Step S2) to remove the low frequency component (DC component) from Next, the ripple amplitude at each ripple frequency is calculated (step Ss). The calculation results are output by an appropriate method such as display (step Ss).

Although it is possible to use a dedicated circuit for AM detection, a spectrum analyzer or the like can also be used as a detector. Furthermore, it is also possible to perform automatic measurements by connecting a microcomputer to the wave detector.

[Effects of the Invention] The number of satellite broadcast receivers using communal reception, such as apartment complexes, is currently increasing, and there are many facilities where deterioration in received image quality is observed due to ripples in frequency characteristics in wired transmission lines for communal reception. Therefore, in a situation where the number of receivers will further increase in the near future, it will be desirable to be able to measure characteristics without interrupting the broadcast wave, but with conventional measurement methods, the broadcast wave has no choice but to be interrupted.

In contrast, in the present invention, since the broadcast wave itself is used as the measurement signal, measurement can be performed without interrupting the broadcast wave at terminals other than the measurement terminal.

The main cause of the ripple is the impedance mismatch that occurs at the joints between cables, connectors, distributors, and other equipment, and by clarifying the ripple characteristics, the location of the mismatch can be estimated. The present invention is extremely effective as a practical measure for improving reception.

[Brief explanation of the drawing]

Figure 1 shows a block diagram for generating comparison data, Figure 2 shows an example of a transmission line under test, and Figure 3 shows data obtained at each measurement point in Figures 1 and 2. FIG. 4, which is a diagram showing the relationship between frequencies, is a diagram showing an example of the processing procedure according to the present invention. 2... BS antenna, 4... BS converter, 6... Coaxial cable, 8... Power supply section, 10... Narrowband AM detector, 12... Logarithmic converter, 20... BS booster, 22.24...Mixer, 26...Distributor, 28-34...Each terminal of series unit, R...Terminal resistor.

Claims (1)

[Claims] 1) In measuring the frequency amplitude characteristics of a high-frequency transmission signal on a transmission path, the transmission signal is input over a certain period of time to a calibration transmission path having known frequency characteristics, and the transmission signal is transmitted at certain intervals. Narrowband AM detection is performed for each frequency of , to determine each maximum test level during the certain period, and by correcting each maximum test level based on the known frequency characteristics, the calibration transmission line is Find the maximum level for each frequency of the input transmission signal, store the logarithmic value of the level as comparison data, input the transmission signal to the transmission line under test for a period equivalent to the certain period, and As in the case of the calibration transmission line, perform narrowband AM detection to find the maximum measurement level for each frequency, find the difference between the comparison data and the logarithm value of each maximum measurement level, and perform numerical calculation processing. A measuring method characterized in that the ripple frequency and ripple amplitude in the frequency amplitude characteristic of the transmission path are measured by performing the following steps.