4.3 Java1484-spectrum analysis using java, complex spectrum and  (Page 2/14)

• ForwardRealToComplex01 - Class that implements the DFT algorithm for spectral analysis.
• Graph03 - Used to display various types of data. (The concepts were explained in an earlier module.)
• Graph06 - Also used to display various types of data in a somewhat different format. (The concepts were also explained in an earlier module.)

Discussion and sample code

The program named Dsp034 , when run in conjunction with either Graph03 or Graph06 computes and plots the amplitude, real, imaginary, and phase angle spectrum for a pulsethat is read from a file named Dsp034.txt . If that file doesn't exist in the current directory, the program uses a set of defaultparameters that describe a damped sinusoidal pulse. The program also plots the pulse itself in addition to the spectral analysis results listed above.

The order of the plotted results

When the data is plotted (see Figure 2 ) using the programs Graph03 or Graph06 , the order of the plots from top to bottom in the display is:

• The pulse
• The amplitude spectrum
• The real spectrum
• The imaginary spectrum
• The phase angle in degrees

Parameter file format

Each parameter value must be stored as characters on a separate line in the file named Dsp034.txt . The required parameters and their order and type are as follows:

• Data length as type int
• Pulse length as type int
• Sample number representing zero time as type int
• Low frequency bound as type double
• High frequency bound as type double
• Sample values for the pulse as type double or int (they are automatically converted to type double if they are provided as type int )

The number of sample values for the pulse must match the value for the pulselength.

Format for frequency specifications

All frequency values are specified as a double representing a fractional part of the sampling frequency. For example, a value of 0.5specifies a frequency that is half the sampling frequency.

Sample parameters for testing

Figure 1 provides a set of sample parameter values that can be used to test the program. This sample data describes a triangular pulse. Be careful when youcreate the file containing these values. Don't allow blank lines at the end of the data in the file.

The plotting programs

The plotting program that is used to plot the output data from this program requires that the program implement GraphIntfc01 .

(I explained the plotting programs and this interface in earlier modules.)

For example, the plotting program named Graph03 can be used to plot the data produced by this program. When it is used, the following shouldbe entered at the command-line prompt:

Spectral analysis

A static method named transform belonging to the class named ForwardRealToComplex01 is used to perform the actual spectral analysis.

(I explained this class and the transform method in the earlier module titled Spectrum Analysis using Java, Sampling Frequency, Folding Frequency, and the FFT Algorithm . However, I skipped over that portion of the method that computes the phase angle. I will explain that portion of the transform method in this module.)