Plotting frequency with different vector error

I am trying to plot a frequency graph with the center at the origin but I keep getting the error that the two vectors are different lengths. Is there anyway to fix this?

[Walter Roberson]

What is size() of your independent variable? What is size() of your dependent variable? Which plotting routine are you using?

[Jack Song]

This is the Code Im using, im not sure what the sizes are. I tried to use the 'origin' function and the limits but it still didnt work. If you could look at it it would be great thank you.

fs =48000; %sampling frequency
Ts= 1/fs; %sampling duration
symbolrate = 1000; %transmitted pulses/second should be an integer divisor of fs
symbol_length = fs/symbolrate; %number of samples in one symbol

pulse = ones(1,symbol_length); %1 pulse hamm/hann delete 1
textin = input('Enter ASCII text for transmission: ' , 's'); % textin can be anything
data_input = dec2bin(double(textin)); %change txtin which is 10# to 2#
[number,length_data] = size(data_input);
data0 = reshape(data_input' , 1,number*length_data); %change the data of matrix to row vector
[number,length_data] = size(data0);

for i = 1:length_data %change 1 bit to 2bit for 4pam 
    data(i) = bin2dec(data0(i));
end


[number, length0] = size(data);
symbol = 2*data-1; % process of 2PAM need to change for OOK and for 4PAM

for i = 1: length0
    for j=1:symbol_length
        signal((i-1)*symbol_length + j) = symbol(i) * pulse(j);
    end
end
index = -Ts/2: Ts: ((length0*symbol_length)-1)*Ts; %Change length of data
 
%  spectrum_index = -fs/2:fs/2; ((length0*symbol_length)-1)*fs
% index = -Ts/2: symbol_length
freq=fft(signal);
freq=fftshift(freq);


figure(1);
% graph= zeros 
plot(index, signal); %time delay in front of line 39

axis([0 1.5*length0*symbol_length*Ts -2 2]);
xlabel('time');


ylabel('amplitude');
title('basband transmission signal of 2PAM');

figure(2);
plot(abs(freq));
hold on
 grid on
 x=linspace(-200,200) ;
 y=linspace(0,0) ;
 plot(x,y,'k-') ;
 plot(y,x,'k-') ;
ax = gca;
ax.XAxisLocation = 'origin';
ax.YAxisLocation = 'origin';
% PlotAxisAtorigin(index,signal)
xlabel('frequency');
% xlim([-10, 600])
ylabel('magnitude');
title('spectrum of 2PAM signal');

[Walter Roberson]

What input are you using? When I tried in R2020a on Mac and used 'hello' as the ASCII input, I had no problem.

Answer 1

[Amrtanshu Raj]

Hi,

To get the desired shift so that the graph is symmetric about the origin, you can make the following changes in your code where you plot the ‘freq’ variable:

sz = length(freq)/2; 
k = [-sz:-1,1:sz]; 
plot(k,abs(freq));