Question T7B04
From subelement T7 - T7B
Which of the following could you use to cure distorted audio caused by RF current on the shield of a microphone cable?
Why is this correct?
A ferrite choke is correct because it specifically blocks RF currents that flow on cable shields. When RF energy couples onto the microphone cable's shield during transmission, it causes audio distortion. The ferrite choke acts as a high impedance to these unwanted RF currents while allowing normal audio signals to pass through unaffected. Band-pass and low-pass filters work on transmitted signals, not cable shield currents, while a preamplifier would actually amplify the problem.
Memory tip
Remember the key pattern: when RF problems involve cables picking up stray energy, think 'choke' solutions. Filters address frequency content of signals, but chokes address unwanted currents on conductors. This distinction helps across many interference questions.
Learn more
Ferrite chokes are essential RFI suppression tools in amateur stations. They create high impedance at RF frequencies while presenting low impedance to desired signals. Install them on power cords, audio cables, and feedlines near equipment to prevent common-mode currents. The ferrite material's magnetic properties make RF currents 'work harder' to flow through the choke, effectively blocking them. This is different from filtering, which addresses signal content rather than unwanted current paths.
Think about it
Why do you think a ferrite choke works on the shield but doesn't interfere with the audio signal flowing through the center conductor of the microphone cable?