Getting two components for one frequency in FFT

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632541 2021-4-21

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https://ww2.mathworks.cn/matlabcentral/answers/808470-getting-two-components-for-one-frequency-in-fft

评论： Bjorn Gustavsson 2021-4-21

采纳的回答： Bjorn Gustavsson

Hi,

I'm getting 2 freq in fft .

But I have signal at 1MHz. Getting peak at 999000 and next is at 1MHz.(other frequencies are also there , 10k, 50k, 500k. For these peak is same as signal frequency.)

Sampling freq is 5MPs.

What is happening at 1MHz ?

Any reason for this?

Please clarify this.

Thank you..

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632541 2021-4-21

Here is the code i have written .

Number of samples= 50000 samples.

fs=50000000; %Sampling frequency

nfft=length(m);

%nfft=2^nextpow2(nfft);

X=fft(m,nfft); %FFT of the signal

X=X(1:nfft/2);

%take magniutde

mx=abs(X);

f=(0:(nfft/2)-1)*fs/nfft; %Frequency range

figure(1);

n=50000;

t=0:1:(n-1);

plot(t,m);

title('Multisine')

xlabel('Samples')

ylabel('Amplitude');

figure(2)

plot(f,mx);

title('FFT of signal')

xlabel('Frequency')

ylabel('Amplitude');

632541 2021-4-21

Any code alterations needed?

Or other solution?

Please provide your suggestions...

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采纳的回答

Bjorn Gustavsson 2021-4-21

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/808470-getting-two-components-for-one-frequency-in-fft#answer_680525

The fft is a circular Fourier transform, there will always be some spectral leakage from frequencies that are not exactly periodic over your data-sample-array. That is what you see here.

HTH