[Ronbo]

Actually the best filter would be a combination of a choke (coil) in series and a capacitor in paralell. Chokes work much better at blocking the pulses than caps do.

If you have a 2-way radio shop near you stop by and see if they have any of the Motorola filter kits. The car battery is basically like a huge capacitor and provides most filtering in your electrical system but high frequency spikes can still ride on the system. The choke filters by magnetic fields as opposed to static fields like caps.

The secondary (low voltage) winding on a power transformer will also work.