This is the resonant frequency. The correct size capacitor is one where the frequency we wish to bypass is the same or less than the resonant frequency. Typically, an alternator filter uses a .5 to 50 microfarad capacitor. Cessna has a 5.72 microfarad capacitor filter available as part number S1915-1. The best types of capacitors for filtering are ceramic and tantalum capacitors, ceramic for the picofarad range and tantalum for the microfarad range.
Electrolytic capacitors are relatively poor noise filters, and also have a short life.
Notice that lead length has a significant effect on the capacitor's resonant frequency. But with 1 inch leads, it resonates at 50 MHz. So capacitor lead lengths used in filter circuits should be kept as short as possible. Inductive filters The other way to filter radio noise is to block the ripple with a series inductor. The most common style of inductor for noise filtering is a ferrite core.