Hi, My signal is 50Hz and 175Hz (about 20% of 50Hz), Sampling 25600 samples/Sec. Implemented with 4096 pointFFT. I am getting 50Hz spectrum @8th location and expecting 175Hz at 28th location. but it is distributed to 24 & 30. other spectrum shows zero

UA.1 · ‎2021-03-26

Can any one help me on this. thanks in advance

gregstm · ‎2021-03-26

In this situation I would capture a snapshot of the sampled input data and the corresponding output of the FFT (into arrays) and then send them to a PC (I use RS232). Then I would use spreadsheets or online FFT tools or MatLab (or even write your own FFT routine) to look at the input data and see what these other FFT routines produce with the same data. Another alternative, record the input signal and plug it into Wavosaur - it's a free audio editing which has a spectrum tool (FFT) where you can easily control all the parameters and see the results. The 24th value corresponds to a frequency of 150Hz, which could be a harmonic of the 50 Hz (depends on whether your signal is a pure sine wave or other).

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gregstm · ‎2021-03-26

In this situation I would capture a snapshot of the sampled input data and the corresponding output of the FFT (into arrays) and then send them to a PC (I use RS232). Then I would use spreadsheets or online FFT tools or MatLab (or even write your own FFT routine) to look at the input data and see what these other FFT routines produce with the same data. Another alternative, record the input signal and plug it into Wavosaur - it's a free audio editing which has a spectrum tool (FFT) where you can easily control all the parameters and see the results. The 24th value corresponds to a frequency of 150Hz, which could be a harmonic of the 50 Hz (depends on whether your signal is a pure sine wave or other).

UA.1 · ‎2021-03-28

Thanks you so much for the feedback. i tried the same. Looks like I am missing some samples