When using a spectrum analyzer to look for non-Wi-Fi interference sources, you notice significant interference across the entire 2.4 GHz band (not on a few select frequencies) within the desktop area of a users workspace, but the interference disappears quickly after just 2 meters. What is the most likely cause of this interference?
The most likely cause of significant interference across the entire 2.4 GHz band within a limited range (disappearing quickly after 2 meters) is a USB 3 device in the user’s work area. USB 3.0 devices are known to emit broadband noise in the 2.4 GHz band, which can cause significant interference to Wi-Fi signals. The interference is typically localized around the device and diminishes quickly with distance, consistent with the observation described in the question.
Option A is the correct answer, as USB 3.0 devices can create significant RF interference in the 2.4GHz band. (See CWNA-107 study guide, page 270) Option B is wrong because while Bluetooth devices are a source of non-WiFi interference, their range goes beyond 2 metres, thus whatever interference they might have caused would go far beyond the user's workspace and not disappear after just 2 metres away from his desktop area. Option C is wrong in the sense that RF energy coming from an AP, though possibly an interference source, cannot be regarded as a non-WiFi interference as the AP is a WiFi device. As for Option D, I'd like to think that the concept of unintentional radiation is related to antennas and similar devices, and has no connection to Electric power supply.
I think all of them could fit as potential answers.