## ifft one side spectrum to get a real signal

### Tsuwei Tan (view profile)

on 8 Oct 2019
Latest activity Answered by Samatha Aleti

on 16 Oct 2019

### Samatha Aleti (view profile)

Dear Matlab Profession,
I have a code to generate a one side spectrum in frequency domain, I am not sure it is postive frequency or negative frequency.
But I do know the energetic portion of signal in time domain aftfter ifft must starts after 3.33 sec as either Figure (1) or (2).
The issue is based on Fourier transform theory, I should get a "real" signal, but I still get a complex signal in time domain.
May I ask how to fix it or use ifftshift? Thank you!
clear;clc;close all;
%% This is the time and frequency steps used to generate signals
sig_end=7; % in sec, r/cw=5000/1500=3.33 sec arrival already covered
Fs=400; % Sampling Freq, Fs/2 is the folding freq
dt=1/Fs; % Time Step
L=Fs*sig_end; % Signal Length: Fs* a number
t=(0:L-1)*dt; % physical time (s)
df=Fs/L; % frequency step
%% Load one side spectrum generated from software
Pr_other_side=conj(Pr);
Pr_two_sides_1=cat(1,Pr_other_side(2:end-1),flip(Pr));
Pr_two_sides_2=cat(1,Pr_other_side,flip(Pr(2:end-1)));
pr_two_sides_1=ifft(Pr_two_sides_1);
pr_two_sides_2=ifft(Pr_two_sides_2);
figure(1)
plot(t,pr_two_sides_1);
xlabel('Time (sec)');ylabel('Arbitrary magnitude')
figure(2)
plot(t,pr_two_sides_2)
xlabel('Time (sec)');ylabel('Arbitrary magnitude')

R2018b