ACMA RF Principles 5 — Questions and Answers
Question 1: What is the purpose of Transmit Power Control (TPC) in Aruba wireless networks?
- To manually set a fixed transmit power on all APs to ensure uniform coverage
- To dynamically adjust AP transmit power to minimize co-channel interference while maintaining coverage (Correct answer)
- To boost transmit power above regulatory limits in high-density environments
- To synchronize power levels between the controller and APs
Correct answer: To dynamically adjust AP transmit power to minimize co-channel interference while maintaining coverage
TPC automatically adjusts AP transmit power levels to reduce interference between APs while ensuring clients maintain sufficient coverage throughout the network.
Question 2: What RF characteristic determines how much an RF signal is scattered when it strikes a rough or irregular surface?
- Absorption
- Reflection
- Scattering (Correct answer)
- Diffraction
Correct answer: Scattering
Scattering occurs when RF signals strike irregular or rough surfaces, causing the energy to disperse in many directions rather than reflecting cleanly.
Question 3: Which of the following correctly describes the concept of half-power beamwidth for a directional antenna?
- The angle at which the antenna radiates exactly half the total power of an omnidirectional antenna
- The angular width of the antenna's main lobe measured between the -3 dB points on each side (Correct answer)
- The total angle swept by the antenna during beam steering operations
- The bandwidth in MHz that the antenna can transmit at its rated gain
Correct answer: The angular width of the antenna's main lobe measured between the -3 dB points on each side
Half-power beamwidth is the angular width of an antenna's main lobe measured between the two points where power drops to half (-3 dB) of the peak value.
Question 4: What is diffraction in the context of RF propagation?
- The increase in signal strength caused by antenna alignment
- The ability of RF waves to bend around obstacles and edges (Correct answer)
- The reduction in signal speed caused by dense building materials
- The conversion of RF energy into electrical current at the antenna
Correct answer: The ability of RF waves to bend around obstacles and edges
RF diffraction allows radio waves to bend around the edges of obstacles such as buildings or hills, enabling signals to reach areas not in the direct line of sight.
Question 5: In the 5 GHz band, approximately how many non-overlapping 20 MHz channels are available in the U.S. (including UNII-1, UNII-2, UNII-2e, and UNII-3)?
- 3
- 11
- 24 (Correct answer)
- 45
Correct answer: 24
The 5 GHz band in the U.S. offers approximately 24 non-overlapping 20 MHz channels across the UNII-1, UNII-2, UNII-2e, and UNII-3 sub-bands.
Question 6: What is the main RF challenge introduced by deploying APs in a high-density environment such as a stadium or conference center?
- Insufficient AP transmit power to cover the venue
- Co-channel interference caused by many APs operating on the same or adjacent channels in close proximity (Correct answer)
- Lack of 802.11ac support in high-density venues
- Inability to use directional antennas indoors
Correct answer: Co-channel interference caused by many APs operating on the same or adjacent channels in close proximity
In high-density environments, the close proximity of many APs creates significant co-channel and adjacent channel interference, requiring careful channel planning and reduced transmit power.
Question 7: What does the term 'link budget' encompass in a wireless network design?
- The financial cost of deploying APs across a site
- The total calculation of all gains and losses in an RF link to determine if a connection will be reliable (Correct answer)
- The maximum number of client associations an AP can support
- The monthly data transfer capacity allocated to a wireless segment
Correct answer: The total calculation of all gains and losses in an RF link to determine if a connection will be reliable
A link budget accounts for transmit power, antenna gains, cable losses, path loss, and receiver sensitivity to determine whether a wireless link will achieve the required SNR.
ACMA RF Principles 5
What is the purpose of Transmit Power Control (TPC) in Aruba wireless networks?