JPS5841473B2 - How to use this service - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency characteristic measuring device that sweeps the frequency characteristic of the amplitude or delay of a communication line using a sine wave or a cosine wave, and displays the frequency characteristic using an oscilloscope.

The overall amplitude and delay characteristics of a communication line are a combination of the amplitude and delay of each part of the line, and generally have first-order and higher-order slope distortions, which degrade the transmission characteristics of the line.

Particularly in digital communication systems, deterioration in transmission characteristics due to distortion of the first-order slope of amplitude and delay is greater than deterioration due to other higher-order distortions.

For this reason, an equalizer for -order gradient distortion is provided to compensate for distortion and reduce deterioration.

Conventional frequency characteristic devices cannot measure the first-order slope and the higher-order slope of distortion separately, so it takes a long time to adjust the equalizer.

In order to eliminate such drawbacks, the present invention provides a filter whose passband is a sweep frequency and a changeover switch for inserting or removing this filter in the vertical axis manual section of the oscilloscope in the receiving section of the frequency characteristic measuring device. , the total frequency characteristic and the next slope of the total frequency characteristic can be selected and displayed, and its purpose is to facilitate the evaluation of the frequency characteristic of the transmission path and the adjustment of the equalizer.

The principle of measuring only the first-order inclination amount from characteristics having -order and higher-order distortions will be described.

Since the amplitude and delay are exactly the same, only the delay characteristics will be described below.

The sweep width of the angular frequency is 2jω. The sweep period is T, and the center frequency is ω.

Then, the angular frequency ω at time t is given by equation (1).

The delay frequency characteristic τ(O)) within the measurement band is expressed by the general formula (2
) can be expressed as a polynomial.

Here, τi is the coefficient of the i-th delay.

Also, i=0 is an O-order delay, that is, a term that does not have frequency characteristics, so it will be omitted.

From equations (1) and (2), equation (3) is obtained. Formula (3)
The power of the cosine function in %os (2π; 7) 1 't-JfRIC constant 9.8 period"゛7 cosine wave゛080
Represented by harmonics.

Sweep frequency components with a period of ↑ are generated from odd-order terms in equation (3), but the higher the order, the smaller the absolute value.

Therefore, if we ignore what arises from terms of order three or higher, we get
The sweep frequency components are only those generated from the - next term in equation (3), resulting in equation (4).

Therefore, by extracting only the sweep frequency component from the measured value and adding this to the vertical axis of the oscilloscope and the cosine wave of the sweep frequency to the horizontal axis, we can draw a Lissajous figure, thereby creating a first-order delay corresponding to the first-order slope amount. The coefficient τ1 can be measured.

The operation will be explained below using the drawings.

. FIG. 1 shows an embodiment of the present invention, in which 1 is a frequency characteristic measuring device transmitting section, 2 is a transmitting section, 3 is a frequency characteristic measuring device receiving section, 4 is an amplitude or delay characteristic detector, 5 is a filter, 6
is an indicator.

Figure 2 shows the conventional characteristics without inserting a filter;
The figure shows the amount of primary slope measured by inserting a filter.

To measure the frequency characteristics of the transmission line 2, the transmitter 1 transmits a frequency-swept signal to the transmission line 2.

In the receiving section 3, the amplitude or delay characteristic detector 4 detects the signal and adds it to the vertical axis (■) of the oscilloscope on the display 6.

A sine wave of a swept frequency obtained by an amplitude or delay characteristic detector 4 is added to the horizontal axis H.

The frequency characteristics of the transmission line will be displayed on the display 6 if the filter 5 is not inserted due to ripples and dispersion characteristics caused by mismatching of various parts.
The characteristic shown in Figure 2 is displayed on the cathode ray tube of the oscilloscope1.As mentioned above, the primary slope of the characteristic shown in Figure 2 is required for equalizer adjustment, so the passband is When a filter 5 with a sweep frequency is included, only the primary slope amount can be measured as shown in FIG.

Note that when it is desired to display the amount of secondary slope, the passband frequency of the filter may be made twice the sweep frequency, and when only ripples are desired to be displayed, a filter with a frequency corresponding to the ripples may be used.

Note that it is desirable that the phase characteristics of the filter be in phase at the input end and the output end in the pass band so that the phases of the vertical and horizontal axes of the oscillogram do not change when the changeover switch is changed.

As described above, the present invention has the advantage of being able to select and measure the necessary information, making it extremely easy to evaluate characteristics and quickly adjusting the distortion equalizer.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, in which 1 is a transmitting section of a frequency characteristic measuring device, 2 is a transmission line, 3 is a receiving section of a frequency characteristic measuring device, 4 is an amplitude or delay characteristic detector, 5 is a filter, 6 is an indicator. Figure 2 shows the conventional characteristics without inserting a filter;
The figure shows the amount of primary slope measured by inserting a filter.

Claims (1)

[Claims] 1. In a frequency characteristic measuring device that sweeps the frequency with a sine wave or a cosine wave and displays the frequency characteristics with an oscilloscope, the sweep frequency of the measuring device is set as a passband in the vertical axis input section of the oscilloscope of the measuring device, A filter whose phase characteristics at the sweep frequency are in the same phase at the input end and the output end, and a switch for inserting or removing the filter in the circuit are provided, and the total frequency characteristic and the primary slope of the total frequency characteristic of the line under test are controlled by the switch. A frequency characteristic measuring device characterized in that the frequency characteristics are selected and displayed by switching.