CWS CWS Basic RF Principles 5

Question 1

In the 2.4 GHz band (802.11b/g/n), how many non-overlapping 20 MHz channels are available in the US?

Accepted Answer

3

Answer

In the US, the 2.4 GHz band has only 3 non-overlapping 20 MHz channels: 1, 6, and 11.

Question 2

What is the primary advantage of OFDM (Orthogonal Frequency Division Multiplexing) over single-carrier modulation?

Accepted Answer

Robustness against multipath interference due to long symbol duration

Answer

OFDM uses many narrow subcarriers with long symbol durations, making it far less susceptible to multipath-induced intersymbol interference.

Question 3

Which unit is used to express absolute RF power levels referenced to 1 milliwatt?

Accepted Answer

dBm

Answer

dBm expresses power relative to 1 mW; 0 dBm = 1 mW, positive values are greater than 1 mW, negative values are less.

Question 4

A signal loses 6 dB passing through a wall. If the original signal is 20 dBm, what is the power after the wall?

Accepted Answer

14 dBm

Answer

Power after the wall = 20 dBm − 6 dB = 14 dBm; dB losses are subtracted directly in the log domain.

Question 5

Co-channel interference (CCI) in a wireless LAN is best reduced by:

Accepted Answer

Assigning non-overlapping channels to adjacent access points

Answer

Using non-overlapping channels on neighboring APs eliminates the co-channel interference caused by APs sharing the same frequency.

CWS Exam Practice Test