CWS Basic RF Principles Flashcards

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

Answer: 3

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

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

Answer: Robustness against multipath interference due to long symbol duration

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

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

Answer: dBm

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

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

Answer: 14 dBm

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

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

Answer: Assigning non-overlapping channels to adjacent access points

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

What is the effect of increasing antenna cable length on an RF link?

Answer: Increases insertion loss, reducing effective transmit power

Longer cables have more resistive and dielectric losses, reducing the power delivered from the radio to the antenna.

Which RF phenomenon is primarily responsible for indoor 'dead spots' where signal strength drops sharply despite short distances from the AP?

Answer: Multipath destructive interference

Indoor dead spots are typically caused by multipath signals arriving out of phase and canceling each other through destructive interference.