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I am currently operating in vhf band AND trying to detect frequencies using Fast Fourier transform thresholding method. While detection of multiple frequencies , i received spurs(May not appropriate word) in addition with original frequencies, Such as in case of f1,f2 that are incoming frequencies i also receive their sum f1+f2 and difference f1-f2.

i am trying to eliminate these using thresholding method but i can't differentiate them with real real frequency magnitudes. Please suggest me some method, or methodology to eliminate this problem

Input frequencies F1, F2 Expected frequencies F1,F2 Receive frequencies ,F1,F2,F1-F2,F1+F2

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    $\begingroup$ Sounds like you are experiencing intermodulation, which are usually due to nonlinearities of your system. No easy way to avoid them, what you are going to need to estimate their severity is calibration to estimate a nonlinear model of your system, e.g., coefficients of a polynomial (NB: they might be frequency-dependent). $\endgroup$ – Florian Jul 19 '19 at 12:31
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    $\begingroup$ try a lower gain $\endgroup$ – user28715 Jul 19 '19 at 13:17

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