How to plot the spectrum of a high frequency sine wave of above 1GHz

Question

Praveen kumar 2014-2-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/115995-how-to-plot-the-spectrum-of-a-high-frequency-sine-wave-of-above-1ghz

评论： Praveen kumar 2014-2-17

采纳的回答： Wayne King

Please help me with the matlab code

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Answer 1

Wayne King 2014-2-13

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https://ww2.mathworks.cn/matlabcentral/answers/115995-how-to-plot-the-spectrum-of-a-high-frequency-sine-wave-of-above-1ghz#answer_124235

在 MATLAB Online 中打开

Do you have the Signal Processing Toolbox:

Fs = 4e9;
t = 0:1/Fs:0.001-(1/Fs);
x = cos(2*pi*1.5e9*t);
[Pxx,F] = periodogram(x,[],length(x),Fs,'power');
plot(F,Pxx)

If you do not, you can use fft()

xdft = fft(x);
xdft = xdft(1:length(x)/2+1); % works for even length x
deltaf = Fs/length(x);
freqvec = 0:deltaf:Fs/2;
plot(freqvec,abs(xdft))

Note that latter is not scaled.

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Praveen kumar 2014-2-14

After performing autocorrelation to sinusoidal signal, i'm not getting the spectrum at high frequencies.

Praveen kumar 2014-2-17

在 MATLAB Online 中打开

I have written the following code inorder to determine the Spectrum of autocorrelated noisy sine signal. But, I'm not able to get the spectrum for higher frequencies above 1MHz. Please inform where i have to change the code... close all; clear all; clc; %% Time specifications: Fs = 1e4; % samples per second dt = 1/Fs; % seconds per sample StopTime = 1; % seconds t = (0:dt:StopTime-dt)'; N = size(t,1);

   %%Sine wave:
   Fc = 1e3;                       % hertz
   x = sin(2*pi*Fc*t);
   noisy_x = x + 0.5*randn(size(x));
   y = xcorr(noisy_x,5e3,'biased');
   display(size(y));
   subplot(2,1,1);
   plot(t,x);
   title('Sine signal');
   subplot(2,1,2);
   plot(t,noisy_x);
   title('Noisy signal');
   %%Fourier Transform:
   X = fftshift(fft(y));
   %%Frequency specifications:
   dF = Fs/N;                      % hertz
   f = -Fs/2:dF:Fs/2;           % hertz
   display(size(f));
   display(size(X));
   %%Plot the spectrum:
   figure;
   plot(f,abs(X)/N);
   xlabel('Frequency (in hertz)');
   title('Autocorrelation spectrum');