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. These come in many different styles but typically the wire with the noise currents is wrapped around the core, creating an inductor in series with the circuit. DC current passes through the core but high frequency currents induce a magnetic field in the ferromagnetic material of the core. This magnetic field raises the impedance and effectively blocks noise currents.
Ferrites are effective on radio power input leads and strobe power input leads.
In the first case they prevent noise currents from entering the radio, and in the second case they prevent noise currents from exiting the strobe. To be effective, ferrite impedance must be larger than circuit impedance. To filter the output of an alternator would required an impractically huge ferrite core. So alternator voltage ripple is usually bypassed to ground by use of a capacitor. However, ferrites are simple to use and have an amazing filtering ability.