Question
How can conducted noise from an automobile battery charging system be suppressed?
Answer Options
- A) By installing filter capacitors in series with the alternator leads
- B) By installing a noise suppression resistor and a blocking capacitor at the battery
- C) By installing a high-pass filter in series with the radio’s power lead and a low-pass filter in parallel with the antenna feed line
- D) By installing ferrite chokes on the charging system leads
Correct Answer: D
Explanation
Conducted noise from an automotive charging system (alternator, voltage regulator) is high-frequency noise that travels along the vehicle’s electrical wiring, including the power leads to the radio. This noise must be blocked from traveling along the power cables to the receiver. A common and effective method involves increasing the impedance of the electrical leads at the noise frequencies.
The most practical and effective method is to install ferrite chokes on the charging system leads (both positive and ground). Ferrite material provides high impedance to RF energy, effectively choking off the unwanted high-frequency noise and preventing it from propagating along the electrical system into the radio’s power input. Ferrites are typically used in conjunction with bypass capacitors.
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