finding time domain of an excel FFT data

I have an Excel file of a signal FFT including frequency, amplitude and phase.

How can I find the Time domain (Time series) of this signal?

Answer 1

[Shaik mohammed ghouse basha]

Hi @Amirhossein Fathi,

I understand that you have an exceel sheet which has Amplitude and Phase of set of frequency components and from this frequency data you want to get the time series data of the signal.

I took first 10 samples and tried at my end. This code works fine:

T = readtable('FrequencyData.xlsx');  %read the excel file as a table of data

numSamples = size(T,1);               %returns number of rows i.e. number of differency frequencies 

frequencyCoefficients = [numSamples]; %Convert polar form of each frequency component into complex number notation

for i=1:numSamples                    %iterate over each frequency sample
   
    amp = table2array(T(i,2));        %access amplitude and angle of a particular frequency   
    ang = table2array(T(i,3));        %T(i,j) of a table returns data type table so type cast it into array for using it as a number 
    
    frequencyCoefficients(i) = amp*cos(ang) + 1i*amp*sin(ang);  %A costheta + j A sintheta notation 

end

%Now you have all frequency Coefficients, so apply inverse fast fourier
%transform function on this data to get time series plot.

timeSeries = ifft(frequencyCoefficients, numSamples)

For better understanding of applying inverse fourier transform you can go through ifft .