ACMA RF Principles 2 — Questions and Answers
Question 1: What is the primary cause of multipath interference in a wireless network?
- Excessive transmit power
- RF signals reflecting off surfaces and arriving at the receiver at different times (Correct answer)
- Interference from neighboring APs on the same channel
- Antenna polarization mismatch
Correct answer: RF signals reflecting off surfaces and arriving at the receiver at different times
Multipath occurs when RF signals reflect off walls, floors, and objects, causing multiple copies of the same signal to arrive at slightly different times.
Question 2: Which antenna type radiates power equally in all horizontal directions, making it suitable for open-office deployments?
- Yagi antenna
- Parabolic dish antenna
- Omnidirectional antenna (Correct answer)
- Sector antenna
Correct answer: Omnidirectional antenna
An omnidirectional antenna radiates power equally in a 360-degree horizontal pattern, ideal for providing coverage in all directions from a single point.
Question 3: What does EIRP stand for in the context of wireless networking?
- Effective Isotropic Radiated Power (Correct answer)
- Ethernet Interface Radio Protocol
- Extended Interference Reduction Percentage
- Equivalent Internal Radio Power
Correct answer: Effective Isotropic Radiated Power
EIRP (Effective Isotropic Radiated Power) is the total power radiated by an antenna system, combining transmit power and antenna gain.
Question 4: What RF phenomenon causes signal strength to decrease as distance from the transmitter increases?
- Reflection
- Refraction
- Free-space path loss (Correct answer)
- Absorption
Correct answer: Free-space path loss
Free-space path loss is the natural attenuation of an RF signal as it travels through open space, increasing with both distance and frequency.
Question 5: Which of the following best describes antenna gain?
- The amount of power added by the antenna's internal amplifier
- The increase in signal strength achieved by focusing RF energy in a specific direction (Correct answer)
- The ratio of received to transmitted power across a link
- The sensitivity improvement of the receiver circuit
Correct answer: The increase in signal strength achieved by focusing RF energy in a specific direction
Antenna gain describes how much an antenna focuses RF energy in a particular direction compared to an isotropic radiator, measured in dBi.
Question 6: What is the significance of the Fresnel zone in wireless links?
- It defines the minimum channel width required for a transmission
- It is the elliptical region around the line-of-sight path that must be kept mostly clear to avoid signal degradation (Correct answer)
- It specifies the maximum allowed EIRP for outdoor links
- It is the frequency range used by directional antennas
Correct answer: It is the elliptical region around the line-of-sight path that must be kept mostly clear to avoid signal degradation
The Fresnel zone is an elliptical area around the direct path between transmitter and receiver; obstructions within 60% of the first Fresnel zone cause significant signal loss.
Question 7: Which unit is used to express antenna gain relative to an isotropic radiator?
- dBm
- dBd
- dBi (Correct answer)
- dBW
Correct answer: dBi
dBi (decibels relative to isotropic) measures antenna gain compared to a theoretically perfect isotropic antenna that radiates equally in all directions.
ACMA RF Principles 2
What is the primary cause of multipath interference in a wireless network?