CWS RF Behavior & Signal Propagation 3 — Questions and Answers
Question 1: What term describes the process by which an RF signal bounces off a flat, smooth surface such as a metal wall?
- Diffraction
- Scattering
- Reflection (Correct answer)
- Absorption
Correct answer: Reflection
Reflection occurs when an RF wave strikes a smooth, flat surface and bounces back at an angle equal to the angle of incidence.
Question 2: Which material is known to cause the highest RF signal absorption losses in an indoor environment?
- Glass windows
- Drywall partitions
- Cinder block walls (Correct answer)
- Wood doors
Correct answer: Cinder block walls
Cinder block (concrete masonry) walls cause high RF attenuation, often 10–15 dB or more, making them one of the most significant indoor obstacles.
Question 3: In a point-to-multipoint outdoor wireless deployment, what is the primary propagation concern over long distances that causes signal bending toward the Earth?
- Tropospheric ducting
- Atmospheric refraction due to the k-factor (Correct answer)
- Ionospheric reflection
- Ground-wave propagation
Correct answer: Atmospheric refraction due to the k-factor
The k-factor describes how the Earth's atmosphere refracts RF signals, effectively making the Earth appear larger and affecting line-of-sight clearance calculations.
Question 4: Which antenna property describes the ratio of power radiated in a specific direction versus an isotropic radiator?
- EIRP
- Antenna efficiency
- Antenna gain (dBi) (Correct answer)
- Beamwidth
Correct answer: Antenna gain (dBi)
Antenna gain in dBi expresses how much more signal an antenna radiates in its primary direction compared to a theoretical isotropic radiator.
Question 5: What propagation effect occurs when atmospheric conditions create a layer that traps RF energy close to the Earth's surface, extending range unexpectedly?
- Knife-edge diffraction
- Tropospheric ducting (Correct answer)
- Fresnel zone obstruction
- Rayleigh fading
Correct answer: Tropospheric ducting
Tropospheric ducting traps RF signals in a low-altitude layer, allowing them to travel far beyond their normal range and potentially causing interference.
Question 6: A wireless engineer measures the received signal level at -70 dBm. The noise floor is -95 dBm. What is the SNR?
- 25 dB (Correct answer)
- 165 dBm
- -25 dB
- 70 dB
Correct answer: 25 dB
SNR is calculated by subtracting the noise floor from the signal level: -70 dBm - (-95 dBm) = 25 dB.
Question 7: Which 802.11 MIMO technique uses multiple antennas to transmit identical data simultaneously, improving signal reliability rather than throughput?
- Spatial multiplexing
- Transmit beamforming
- Maximal ratio combining (MRC)
- STBC (Space-Time Block Coding) (Correct answer)
Correct answer: STBC (Space-Time Block Coding)
STBC transmits redundant copies of data across multiple antennas in a space-time coded pattern, improving reception reliability without increasing data rate.
CWS RF Behavior & Signal Propagation 3
What term describes the process by which an RF signal bounces off a flat, smooth surface such as a metal wall?