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How to adjust time scale so that when this code is executed ,in frequency domain plot the frequency axis gives value like 2*10^6 ,3*10^6 not simple 2,3

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M =8; %here we initialize the number of constellation point of qam
no_of_data_points = 128;
data_source= abs(round(randn(1,10)));%here we take random normal function
figure(1);
stem(data_source);
grid on;
xlabel('Data Points');
ylabel('transmitted data phase representation');
title('Transmitted Data'); %here we plot that transmitted data
qam_modulated_data = qammod(data_source, M); %here we perform 8bit qam on the random normal function
scatterplot(qam_modulated_data);
title('MODULATED TRANSMITTED DATA');%here we plot those constellation point
qam_modulated_data1(1:(M/2))=qam_modulated_data(1:(M/2)); %here we introduce another array named qam_modulated_data1 where first four element is first four constellation point
qam_modulated_data1(((M/2)+1):M)=-qam_modulated_data(1:(M/2));% in my qam_modulated_data1 array last four point is Hermitian of first four point
y=fft(qam_modulated_data1); %here we apply fast Fourier transform on the data of qam_modulated_data1 array
figure(3);
stem(y); %here we plot that fft result
grid on;
xlabel('frequency');
ylabel('amplitude');
title('odd frequency suppressed output');
yc=conj(y);
real_y=y.*yc ;
figure(4);
stem(real_y);
grid on;
xlabel('frequency');
ylabel('amplitude of real values of fft');
title('real value of fft');
1.how to make amplitudes positive?
2.what the changes should be done so that freq axis we get 1*10^6,2*10^6 not just 1,2.
please help.
  2 Comments
Dipsikha Roy
Dipsikha Roy on 15 Dec 2020
What command should be used to get a graph like this..i want to see the path as well not only points..scatterplot gives me the point only..can u help me please..🙏

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