% Program to Calculate the FFT of a Single Channel of Data

% Change Directories
cd 'C:\Data'

% Load the Recorded Data into Matlab
load Model.txt

% Read the First Column of the Data File and Store as the Time Array
time = Model(:,1);

% Read the Second Column of the Data File and Store as an Array of Recorded Data
ch1 = Model(:,2);

%Remove Linear Offset from Time History by Detrending
ch1 = detrend(ch1);

% Calculate the Fast Fourier Transform (FFT) of the Data
ch1_f = fft(ch1);

% Determine the Length of the FFT
N = length(ch1_f);

%Calculate delta t by Subtracting Point 2 from Point 1 in the Time Array
deltat=time(2)-time(1)

% Determine the Number of Time Steps in the Data Array
n=length(ch1)

% Calculate the Frequency Increment of the FFT
deltaf=1/n/deltat

%Calculate the Nyquist Frequency
nyq=1/deltat/2

% Build a Frequency Array
f=0:deltaf:nyq-deltaf;

% Go From Complex Form, to Determine the Magnitude of the FFT
% Convert to a Single-Sided FFT - Ignore All Data from i = N/2+1 Through N in the FFT
mag_1 = abs(ch1_f(1:N/2));

% Go From Complex Form, to Determine the Phase Angle of the FFT
angl_ch1 = angle(ch1_f(1:N/2));

% Plot the Single-Sided FFT Magnitude Versus Frequency
plot (f,mag_1)
xlabel('Frequency (Hz)') % X-axis Label
ylabel('Fourier Amplitude') % Y-axis Label
title('FFT of Channel 1 Acceleration Data') % Plot Title