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SPECTRUM ANALYSIS SOFTWARE The programs in this package were written by: Victor DePinto 2627-148th ave. S.E. Apt. 10 Bellevue, Washington 98007 (206) 641-7591 The last revision date was January 27, 1982. These programs provide the capability to perform the FFT and inverse FFT and to perform various arithmetical manipulations on signals as well as to display the results. The data processed by these programs is contained in disk files. Data is also output to disk files except when displayed on CRT or printer. The data is in the form of a sequence of 1024 complex numbers representing 1024 data points in either the time or frequency domain. INSTRUCTIONS FOR USE OF THE FFT PROGRAM This program performs the FFT or inverse FFT on files containing a sequence of 1024 complex values. The user specifies the input and output filenames. Filetypes are .DAT. Enter only the filename, not the filetype. It is necessary that the file FFT.COM be on the disk. To operate this program, type "FFT". The program will ask for source and destination filenames and then will ask for a number specifying FFT or inverse FFT. The program will then perform a 1024 point FFT on the source file and write the result to the destination file. INSTRUCTIONS FOR USE OF THE UTILITY PROGRAM This is a general utility program which allows examination and plotting of file data and performs certain arithmetic operations on the data, such as summing, multiplication, and windowing. In the event that other arithmetic manipulations are required, the user may write FORTRAN programs which operate on 1024 point complex arrays read and written to unformatted disk files. It is necessary that the files UTIL.COM and ARIT.COM be on the disk. To run the utility program, type "UTIL". The program will respond with a menu. Following is a list of the menu items with a brief description of each: -1- 1 WRITE FILE TO CRT Write real and imaginary parts of all values in file to CRT. The user first enters the filename then the first point to be displayed, and types "Q" to quit. Three points are displayed on each line. Each point consists of a real and imaginary part. The first number is the index of the first point displayed. 2 CREATE REAL PULSE FILE Creates a file containing a real constant in a user- specified range of points. All other points are zero, and all imaginary parts are zero. 3 WINDOW FUNCTIONS This will bring up another menu offering to multiply a range of points by any one of a number of popular window functions. 4 ARITHMETIC FUNCTIONS This brings up a menu offering to add, subtract, multiply, or divide two files and place the result in a third file. It will also multply a file by a constant and find the conjugates or magnitude squared of a file. 5 PRINT FILE ON PRINTER Prints real and imaginary parts of of a file on the system list device. 6 RMS VALUE OF REAL PARTS OF A FILE Computes the root mean square of he real parts of a file and writes this value to the CRT. 7 MODIFY FILE This allows the user to enter or modify the data points on a point by point basis. 8 TRANSLATE This rotates (shifts) all data points in a file by user- specified amount. I must apologize for the slowness of this routine. No doubt a clever programmer could make it faster. 9 PLOT FUNCTIONS This brings up a menu offering to make graphic plots of time or frequency domain files. The exact nature of the functions depends on the type of plotting device used. A version is supplied which will make plots on any printer. Another version will make high resolution plots on the Houston Instruments DMP2 plotter. 10 RETURN TO OPERATING SYSTEM Return to CPM. -2- THE PLOTTER INTERFACE The TTY version of UTIL.COM makes character plots on any standard printer. The DMP2 version plots on the Houston Instruments DMP2 plotter. The plotter should be wired for .005 inch per step and 9600 baud serial RS-232C interface. Lower baud rates are permissible, but will slow the pen motion. The plotter serial port must be interfaced to the CP/M BIOS as the PUNCH device. NOTES ON UTILIZATION Certain types of data to be processed by this software may be generated by the utility program itself. (ie. pulses, double pulses, truncated spectra, etc.) Other data will be in files written by user-generated programs or possibly acquired from the real world. A lot of things can be done with a little imagination. Here are some possibilities: To truncate a spectrum, multiply by a real pulse. To filter a signal, multiply it's FFT by the frequency domain filter function. This may be the FFT of the impulse response of the filter. A double pulse may be created by summing two single pulses. Signals may be added and subtracted in either the time or frequency domain. The program may be used to examine the spectra of waveforms in contemplated circuit design, to determine design suitability without lab measurements. The inverse FFT may be used as a tool in the design of FIR filters. One version of my software had a provision for uniform rate data acquisition from an analog to digital converter. This is not provided in the package because of it's hardware- dependent nature, but it could easily be implemented by the user. In order to get the ADC data into a format compatible with this software, write a Microsoft FORTRAN program which defines both an integer array and a floating point array. An assembly language subroutine is linked with the FORTRAN program. By means of data area declared COMMON, the assembly language routine routine fills the integer array with 1024 samples from the ADC. The FORTRAN program will then transfer the data from the integer array to the real parts of the floating point array and write it to disk. The integer numbers will automatically be converted to floating point. The data would then be processed by this software. Thus, with the addition of an analog to digital converter, the computer becomes a Fourier Transform spectrum analyzer. -3- FILE STRUCTURE This software processes data in arrays consisting of 1024 complex data points. Each complex data point consists of two floating point numbers, the real part and the imaginary part. When in memory, these numbers are stored in the following sequence: real part of point 0, imaginary part of point 0, real part of point 1, imaginary part of point 1, and so on. Since each floating point number occupies four bytes, a complex data point occupies 8 bytes. These arrays, or signal vectors, are stored in disk files in internal machine format (not ASCII). This permits much faster access and more compact storage. In general a program will get a 1024 point signal vector to be processed from such an unformatted disk file, and then write the processed data to a similar file. Each disk file occupies 8 kilobytes. Disk filenames are specified by the user. The filetypes are always DAT. If the user writes programs generating data to be processed by this software, it should be stored in memory in a 2 by 1024 array. Element (1,N) is real; element (2,N) is imaginary. The data should then be written to disk using the FORTRAN unformatted write statement. DISK I/O WITH BASIC Compatible data files can be also be read and written to disk using Microsoft BASIC. Since the data must be stored in internal binary form, you must use only random access files. A file must contain 1024 complex values. A file called DISKIO.BAS is included in this package, as an example. COMPILING AND LINKING In order to produce executable object programs, compile the FOR files with the Microsoft FORTRAN-80 compiler and assemble the MAC files with the MACRO-80 assembler. The resulting REL files must then be linked using the L80 linking loader. The final developement work on this package was done with FORTRAN-80 version 3.4. The objective is to produce three COM files: UTIL.COM ARIT.COM FFT.COM FFT.COM performs the 1024 point FFT and inverse FFT by means of a radix-2 Cooley-Tukey algorithm. UTIL.COM is a program which performs various computation and display functions. ARIT.COM is -4- not intended to be run by itself, but is chained by UTIL.COM. A note of explaination is needed with regard to the plotting capabilities of this package. It is possible to make two different versions of UTIL.COM. They are identical except for their plotting functions. The TTY version will make plots on any printer. The DMP2 version produces high resolution plots on the Houston Instruments DMP2 plotter. You will be able to modify the plotting modules of this software to accomodate other types of plotting devices. The chart below shows which source files are needed to produce each COM file. TASK SOURCE FILE MODULE NAMES IN FILE ------------------------------------------------------------- (DMP2 version) UTIL.COM UTIL.FOR UTIL NAME.FOR READ, NAME WIND.FOR WIND, RECTAN, COSBEL, HAFSIN TRIANG, HANNIN, HFSIN3 HAMMIN, COSSQR, PARZEN QCHEK.MAC QCHEK PLOT.FOR PLOT HI.FOR DRAW, HOME, VECTOR GRID, BORDER, SPEED HIA.MAC PRINT, STTIM, PENUP PENDN (TTY version) UTIL.COM UTIL.FOR UTIL NAME.FOR READ, NAME WIND.FOR WIND QCHEK.MAC QCHEK TTYPLOT.FOR PLOT, TTDRAW ARIT.COM ARIT.FOR ARIT NAME.FOR READ, NAME FFT.COM FFT.FOR FFT1K NAME.FOR NAME -5- To facilitate linking of the runtime tasks, four submit files are provided. Before these submit files are used, the FOR and MAC files must be compiled and assembled. To link Type UTIL.COM (TTY vers.) SUBMIT UTIL#T UTIL.COM (DMP2 vers.) SUBMIT UTIL#H ARIT.COM SUBMIT ARIT# FFT.COM SUBMIT FFT# THE TWIDDLE PROGRAM For speed, the FFT program has the needed sine and cosine values initialized in data memory. These values were generated by a FORTRAN program which wrote them to disk in ASCII form. The sines and cosines were then edited into the DATA statement in the FFT.FOR program. The twiddle factor generator program is provided in a file named TWIDDLE.FOR for those who wish to use it to make other FFT programs. -6- FILES SUPPLIED Following is a list of files supplied in this package. Two versions of the executable utility program are supplied. UTIL- TTY.COM plots on any standard printer. UTIL-HI.COM plots on the Houston Instruments DMP2 plotter. Rename the one you want to use as UTIL.COM. FILENAME COMMENTS ARIT.FOR Arithmetic functions. ARIT.COM Executable arithmetic functions. ARIT#.SUB Submit file. DISKIO.BAS Disk file I/O in BASIC. FFT.FOR 1024 point FFT. FFT.COM Executable FFT program. FFT#.SUB Submit file. HI.FOR DMP2 driver. HIA.MAC DMP2 driver. NAME.FOR Filename getter. PLOT.FOR Plotter plot routine. QCHEK.MAC Checks for abort command. SPECTRUM.DOC This documentation. SPECTRUM.TEX TEX input file. TTYPLOT.FOR Printer plot routine. TWIDDLE.FOR Generates twiddle factor table. UTIL.FOR Utility program. UTIL#H.SUB Submit file. UTIL#T.SUB Submit file. UTIL-HI.COM DMP2 version of UTIL.COM. UTIL-TTY.COM TTY version of UTIL.COM. WIND.FOR Window functions. -7-