EASA Module 4 · Filters

RC Filter

An RC network passes some frequencies and blocks others. A low-pass filter passes low frequencies; a high-pass passes high ones. The cut-off is where the output falls to 70.7% (−3 dB): f_c = 1 ÷ (2πRC).

Resistance R 1.6 kΩ

Capacitance C 0.10 µF

Cut-off f_c

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Type

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Roll-off

−6 dB/oct

The cut-off frequency depends only on R and C. Below (low-pass) or above (high-pass) the cut-off the signal passes with little loss; on the far side it is attenuated at −6 dB per octave. These simple filters remove noise, split audio and shape signals throughout avionics.