Even-Order Harmonics: Why Standard APFs Miss Them & How Full-Spectrum Active Filters Stop DC Magnetization Quick Answer: Standard Active Power Filters (APF/AHF) miss even-order harmonics (2nd, 4th, 6th) because their internal Discrete Fourier Transform (DFT) algorithms assume half-wave waveform symmetry ($f(t) = -f(t + T/2)$) to optimize digital signal processor (DSP) cycle throughput, activel...