CWS CWS Basic RF Principles 4 — Questions and Answers
Question 1: Which term describes the gain of an antenna compared to an isotropic radiator, expressed in dBi?
- Antenna gain referenced to isotropic (Correct answer)
- Antenna gain referenced to a dipole
- Antenna insertion gain
- Antenna input gain
Correct answer: Antenna gain referenced to isotropic
dBi expresses antenna gain relative to a theoretical isotropic radiator that radiates equally in all directions.
Question 2: A higher-order modulation scheme like 256-QAM compared to 64-QAM requires:
- A higher SNR to decode reliably (Correct answer)
- Less spectrum bandwidth
- Lower transmit power
- Fewer spatial streams
Correct answer: A higher SNR to decode reliably
256-QAM encodes more bits per symbol but requires a cleaner, higher-SNR signal to distinguish the denser constellation points.
Question 3: What phenomenon occurs when an RF wave passes through the boundary between two media (e.g., air to glass) and changes direction?
- Refraction (Correct answer)
- Reflection
- Diffraction
- Scattering
Correct answer: Refraction
Refraction is the bending of an RF wave as it passes from one medium into another with a different refractive index.
Question 4: What does the term 'noise floor' represent in an RF system?
- The minimum detectable signal level limited by thermal noise and receiver sensitivity (Correct answer)
- The maximum power level that does not cause interference
- The average background signal power in the channel
- The power level at which the amplifier saturates
Correct answer: The minimum detectable signal level limited by thermal noise and receiver sensitivity
The noise floor is the level of background noise below which signals cannot be reliably detected by the receiver.
Question 5: MIMO technology improves wireless throughput primarily by:
- Transmitting multiple independent data streams simultaneously using multiple antennas (Correct answer)
- Increasing the transmit power at the access point
- Using wider channels to carry more data
- Reducing the carrier frequency to improve propagation
Correct answer: Transmitting multiple independent data streams simultaneously using multiple antennas
MIMO uses multiple transmit and receive antennas to send parallel spatial streams, multiplying throughput without additional spectrum.
Question 6: Which factor does NOT directly affect free-space path loss?
- Transmit power (Correct answer)
- Distance between antennas
- Frequency of the signal
- Wavelength of the signal
Correct answer: Transmit power
Free-space path loss depends only on distance and frequency (wavelength); transmit power is a link budget input, not part of FSPL itself.
Question 7: When using a directional antenna, narrowing the beamwidth results in:
- Higher gain in the main lobe direction (Correct answer)
- Lower gain in the main lobe direction
- Wider coverage area
- Reduced EIRP
Correct answer: Higher gain in the main lobe direction
Narrower beamwidth concentrates more energy in a specific direction, increasing the antenna's gain in that direction.
CWS CWS Basic RF Principles 4
Which term describes the gain of an antenna compared to an isotropic radiator, expressed in dBi?