function [t,w,f,W]=myspectrum(in_file)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%This function is a spectrum analyzer
%for tab delimited time-amplitude data
%in an ASCII text file.
%
%S. Mandayam, Rowan University, ECOMMS S'03
%
%Function Input: Filename
%Function Outputs:
%t=time sequence
%w=time domain amplitude
%f=frequency sequence
%W=spectral amplitude
%
%The function assumes that you have
%satisfied the sampling theorem;  i.e.
%fs >= 2 * f_max
%
%Usage: [t,w,f,W]=myspectrum('filename.txt');
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
close all;

%loading input file; separating into time and amplitude
in_signal=load(in_file);
t=in_signal(:,1);
w=in_signal(:,2);
subplot(2,1,1);
plot(t,w);
xlabel('time in seconds');
ylabel('amplitude in volts');
title('Time domain signal');

%calculating parameters for finding spectrum
N=length(t);
T=t(N)-t(1);
dt=T/N;
fs=1/dt;
n=0:N-1;
%setting the frequency axis
f=n/T;
%calculating fft
W=dt*fft(w);
subplot(2,1,2);
plot(f(1:round(N/2)),abs(W(1:round(N/2))));
xlabel(['frequency in Hz; Sampling Frequency = ', num2str(fs), ' Hz']);
ylabel('amplitude in volts');
title('Amplitude Spectrum: My Low Cost Spectrum Analyzer');