UAS Communication Systems and Data Links 2 — Questions and Answers
Question 1: The 5.8 GHz frequency band is most commonly used for which function in UAS systems?
- Command and control (C2) uplink to the aircraft
- Analog or digital video downlink (FPV transmission) (Correct answer)
- GPS satellite signal reception
- Air traffic control voice communication
Correct answer: Analog or digital video downlink (FPV transmission)
The 5.8 GHz band is commonly used for video downlink (FPV) because its higher frequency supports greater bandwidth needed for video, though its range is shorter than the 2.4 GHz C2 band.
Question 2: In UAS communications, what does 'link budget' describe?
- The financial cost of purchasing communication hardware
- The number of simultaneous data channels the system supports
- The accounting of all signal power gains and losses across a communication link to determine reliability (Correct answer)
- The regulatory frequency allocation granted by the FCC
Correct answer: The accounting of all signal power gains and losses across a communication link to determine reliability
A link budget tallies all gains (transmitter power, antenna gain) and losses (path loss, cable loss, atmospheric absorption) to determine whether the received signal will be strong enough for reliable communication.
Question 3: Which antenna type is best suited for UAS ground station use when the aircraft may fly in any direction from the operator?
- High-gain directional Yagi antenna
- Narrow-beam parabolic dish antenna
- Omnidirectional antenna (Correct answer)
- Fixed-sector patch antenna
Correct answer: Omnidirectional antenna
An omnidirectional antenna radiates and receives signal equally in all horizontal directions, eliminating the need to point the antenna at the aircraft as its bearing changes during flight.
Question 4: What is the primary operational impact of RF interference on a UAS control link?
- Increased battery consumption in the aircraft
- Degraded or lost link reliability, potentially causing loss of control (Correct answer)
- Amplification of the GPS positioning signal
- Automatic activation of altitude hold mode
Correct answer: Degraded or lost link reliability, potentially causing loss of control
RF interference from devices operating on the same or adjacent frequencies degrades signal quality, which can cause control dropouts or complete loss of the command link, risking loss of aircraft control.
Question 5: What is the purpose of a 'failsafe' function in a UAS communication system?
- To encrypt the video downlink when streaming to external services
- To automatically increase transmitter power when signal quality drops
- To execute a pre-programmed response (e.g., return-to-home or land) when the C2 link is lost (Correct answer)
- To switch to a backup GPS constellation if the primary signal is unavailable
Correct answer: To execute a pre-programmed response (e.g., return-to-home or land) when the C2 link is lost
Failsafe functions define automatic aircraft behaviors — such as hovering, returning to home, or landing — that activate when the C2 link is lost, preventing the aircraft from flying away uncontrolled.
Question 6: In UAS control systems, what does 'latency' refer to?
- The strength of the received radio signal at the aircraft
- The time delay between a pilot input and the aircraft's execution of that command (Correct answer)
- The rate at which data is transmitted over the control link
- The encryption processing overhead on the flight controller
Correct answer: The time delay between a pilot input and the aircraft's execution of that command
Latency is the round-trip time delay from when a command is sent at the ground station to when the aircraft executes it, which directly affects the pilot's ability to respond to changing flight conditions.
Question 7: Which U.S. regulatory body is responsible for allocating radio frequency spectrum used by UAS communication systems?
- FAA (Federal Aviation Administration)
- FCC (Federal Communications Commission) (Correct answer)
- NIST (National Institute of Standards and Technology)
- NTIA (National Telecommunications and Information Administration) for private users
Correct answer: FCC (Federal Communications Commission)
The FCC governs commercial and private radio frequency spectrum use in the United States, including the ISM bands and licensed frequencies used for UAS command and control systems.
UAS Communication Systems and Data Links 2
The 5.8 GHz frequency band is most commonly used for which function in UAS systems?