Question 3-50F2

Automotive ignition systems generate significant broadband radio frequency (RF) noise due to the rapid voltage changes and high-current sparks. The primary ignition leads carry pulsed DC to the coils, and the secondary leads carry very high voltage to the spark plugs, creating arcs. These fast transitions and arcs are potent sources of RF interference. Ferrite beads are effective RF chokes. When slipped over the primary and secondary ignition leads, they introduce a high impedance to RF currents while allowing the necessary DC and low-frequency ignition pulses to pass through. This impedance absorbs and dissipates the RF noise energy directly at its source, preventing it from radiating and interfering with radio receivers. * **A) In the resistive high voltage cable every 2 years:** While resistive cables help, adding ferrites on them is less direct than on the primary/secondary leads. The "every 2 years" is an arbitrary maintenance schedule and not relevant to the theoretical function of ferrites. * **B) Between the starter solenoid and the starter motor:** This location addresses noise generated by the starter motor itself (e.g., brush arcing), which is a different noise source than ignition noise. * **D) In the antenna lead:** Ferrites on the antenna lead can help prevent common-mode currents on the feedline or filter noise *already picked up* by the antenna. However, it does not suppress the *source* of the ignition noise, which is always the most effective approach.