ACMA RF Principles 4 — Questions and Answers
Question 1: What type of RF interference occurs when two APs operate on overlapping channels in the same area?
- Co-channel interference
- Adjacent channel interference (Correct answer)
- Multipath interference
- Intermodulation distortion
Correct answer: Adjacent channel interference
Adjacent channel interference occurs when two APs operate on channels whose frequency ranges partially overlap, causing cross-channel signal degradation.
Question 2: What is the primary advantage of using a directional antenna over an omnidirectional antenna?
- Directional antennas support more simultaneous client connections
- Directional antennas focus RF energy in a specific direction, providing greater range and gain (Correct answer)
- Directional antennas operate on more frequency bands simultaneously
- Directional antennas eliminate the need for RF site surveys
Correct answer: Directional antennas focus RF energy in a specific direction, providing greater range and gain
Directional antennas concentrate RF energy into a focused beam, increasing range and reducing interference from unwanted directions.
Question 3: What does SNR (Signal-to-Noise Ratio) measure in a wireless network?
- The ratio of the AP's transmit power to its antenna gain
- The difference in dB between the received signal strength and the background noise floor (Correct answer)
- The number of clients connected relative to total AP capacity
- The percentage of packets that arrive without errors
Correct answer: The difference in dB between the received signal strength and the background noise floor
SNR is the difference between the received signal level and the noise floor in dB; a higher SNR indicates a cleaner, more reliable wireless connection.
Question 4: Which 2.4 GHz channels are considered non-overlapping in North America?
- 1, 3, 7
- 1, 6, 11 (Correct answer)
- 1, 5, 9, 13
- 2, 7, 12
Correct answer: 1, 6, 11
In North America, channels 1, 6, and 11 are the only three non-overlapping channels in the 2.4 GHz band, each separated by 25 MHz.
Question 5: What is RF refraction in wireless networking?
- The bouncing of RF signals off smooth surfaces
- The bending of RF signals as they pass through materials with different densities (Correct answer)
- The spreading of RF energy as it travels away from the antenna
- The cancellation of RF signals due to phase differences
Correct answer: The bending of RF signals as they pass through materials with different densities
RF refraction is the bending of a radio wave as it passes through mediums of different densities, similar to how light bends through water or glass.
Question 6: What is the typical receive sensitivity threshold that most enterprise wireless clients require for reliable data transmission?
- -40 dBm
- -67 dBm (Correct answer)
- -90 dBm
- -20 dBm
Correct answer: -67 dBm
A received signal of -67 dBm is the commonly cited threshold for reliable enterprise wireless performance, providing adequate SNR for high data rates.
Question 7: What happens to RF signal polarization when a transmitting antenna is oriented vertically and the receiving antenna is oriented horizontally?
- Signal strength doubles because cross-polarization creates antenna diversity
- Signal loss occurs due to polarization mismatch between the transmitter and receiver (Correct answer)
- The signal automatically converts to circular polarization
- The receiver gains 3 dB of additional signal due to polarization diversity
Correct answer: Signal loss occurs due to polarization mismatch between the transmitter and receiver
Polarization mismatch between transmit and receive antennas causes signal loss of up to 20 dB, because antennas are most efficient when their polarization planes align.
ACMA RF Principles 4
What type of RF interference occurs when two APs operate on overlapping channels in the same area?