The mapping of the test curve of the transformation--EMC of the linear coordinate system to the logarithmic coordinate system

The core function of drawing a test curve is Cemcview::D rawframecurve () function. The function can draw the test curve according to the test frequency band and the test data of the band in the corresponding position of the logarithmic coordinate system. The Drawframecurve () function draws a flowchart of the curve as shown in Figure 1:


Figure 1 Test flowchart

Figure 2 r3131a screen display of linear coordinate system

Each test, the Advantest r3131a spectrometer will sample the measured band 501 points, each point corresponding to the test value is not less than 512, as shown in Figure 3-29. A value greater than 3392 is not displayed on the Spectrometer screen, but it is recorded because the value is also valid. The default longitudinal axis of the Advantest r3131a spectrometer represents 10dB, so the test value of the spectrometer 3392-512=2880 corresponds to 80dB. For a logarithmic coordinate system drawn on a computer, if the longitudinal axis represents 0~m DB, the spectral value corresponding to the maximum value of the logarithmic coordinate system coordinates is:

Set Ytop to the ordinate value on the computer screen corresponding to the upper-left corner of the logarithmic coordinate system, Ybot represents the ordinate value on the computer screen corresponding to the lower-left corner of the logarithmic coordinate system, and y represents the ordinate value on the computer screen corresponding to a test point in the logarithmic coordinate system, and D represents the corresponding spectrometer test value for that test point. The logarithmic coordinate system ordinate starts from 0, then:

So

(3-1)

For the horizontal axis, if the starting frequency of the known test is Fstart, the computer's horizontal axis corresponding to the starting frequency is xstart, the test termination frequency is fstop, the computer horizontal axis of the test termination frequency corresponds to the xstop, and the frequency of the frequency band is Ffrmstart. In conjunction with FIG. 3-16, the corresponding computer coordinates for the starting frequency of the band are:

So

If there are n sampling points in each test band, and there are n test data, then the frequency of the first I data in this band is Fi, and

In the ffrmstop--, the termination frequency of the test frequency band.

The computer axis of the first data corresponds to:

(3-2)

If the test value for the first data in a test band is D, then the computer screen coordinates for that point correspond to (Xi,yi), and Xi and Yi can be calculated separately according to the formula (3-1) and the formula (3-2).

Ps:

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