 The spectrum says there is 5Hz sine wave, too. Where does this come from??
See the spectrum before decimation (Fs=400Hz) again. That has 95Hz in itself.
In case you make x1/4 Down Sampling, this frequency moves to 5Hz, that
is symmetry with respect to new Nyquist frequency (50Hz). That's because
95Hz exceeds the new Nyquist frequency.
Frequencies exceeding Nyquist frequency need to be removed before decimation.
We put RMZLPF(U_8), that is FIR Low Pass Filter designed by Remez Algorithm.
Let's open a monitor window.
The characteristics shows up. This eliminates frequencies more than 50Hz,
i.e. new Nyquist frequency.
Please open a monitor for another FFTMON(U_12) to see filtered spectrum.
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