Given: Before installing a Wi-Fi network, ABC Company performed a spectrum analysis looking for
problems. The 2.4 GHz RF spectrum looked like Image-A. After installing an ERP WLAN, ABC Company
performed another spectrum analysis during business hours. The 2.4 GHz RF spectrum then
looked likeImage-B close to an AP on channel 1.
Now the 2.4 GHz RF spectrum looks like Image-C and access points and clients can no longer
communicate on channel 1. What is happening on channel 1?

A.
The access point’s antenna connectors have been tampered with, causing “spike and shear” RF
transmissions that are not compatible with the OFDM PHY format. For that reason, client devices
cannot receive the AP’s transmissions without error.

B.
A high-power, narrowband RF interference source on channel 1 is causing the CCA energydetects(ED)
function on 802.11 devices to indicate a busy medium because the signal source is above the ED
threshold.

C.
Stronger transmissions from licensed 2.4 GHz users, such as HAM operators, are compressing the
transmissions from the channel 1 access points into the lower portion of the band.

D.
The shape of the signals in images B and C indicates that a licensed user in this frequency range has
enabled the “guard bands” in an effort to restrict local interference with other systems.

E.
Detection of a DFS radar event has discontinued 802.11 operation on channel 1, but the access point’s
Channel Switch Announcement frame cannot be sent due to the presence of radar.