Orthogonal frequency-division multiplexing (OFDM) is a technique used for which types of amateur communication?
The correct answer is A: Digital modes. Orthogonal frequency-division multiplexing (OFDM) is a technique used for digital modes in amateur communication. OFDM is a digital modulation scheme that divides the available bandwidth into multiple orthogonal subcarriers.
OFDM is widely used in modern digital communication systems because it's efficient and resistant to multipath fading. In amateur radio, OFDM is used in digital modes like D-STAR, some digital voice systems, and high-speed data modes. OFDM allows multiple data streams to be transmitted simultaneously on different subcarriers, making efficient use of bandwidth. It's particularly useful for digital modes that need to transmit data reliably over varying propagation conditions.
Exam Tip
OFDM = Digital modes. Remember: OFDM (Orthogonal Frequency-Division Multiplexing) is a technique used for digital modes in amateur communication. It divides bandwidth into multiple orthogonal subcarriers.
Memory Aid
"**O**FDM = **O**n **D**igital **M**odes (think 'OFDM = ODM')"
Real-World Application
You're using a digital voice mode that employs OFDM. The signal is divided into multiple orthogonal subcarriers, each carrying part of the digital data. This allows efficient, reliable digital communication. OFDM is used in various amateur digital modes because it handles multipath and interference well.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. OFDM isn't specifically for extremely low-power contacts. It's a general digital modulation technique used in various applications.
Option C: Incorrect. OFDM isn't specifically for EME (Earth-Moon-Earth) communications. EME can use various modes, but OFDM isn't specifically an EME technique.
Option D: Incorrect. OFDM signals are allowed on amateur bands. They're used in various digital modes and are a legitimate modulation technique.
题目解析
The correct answer is A: Digital modes. Orthogonal frequency-division multiplexing (OFDM) is a technique used for digital modes in amateur communication. OFDM is a digital modulation scheme that divides the available bandwidth into multiple orthogonal subcarriers. OFDM is widely used in modern digital communication systems because it's efficient and resistant to multipath fading. In amateur radio, OFDM is used in digital modes like D-STAR, some digital voice systems, and high-speed data modes. OFDM allows multiple data streams to be transmitted simultaneously on different subcarriers, making efficient use of bandwidth. It's particularly useful for digital modes that need to transmit data reliably over varying propagation conditions.
考试技巧
OFDM = Digital modes. Remember: OFDM (Orthogonal Frequency-Division Multiplexing) is a technique used for digital modes in amateur communication. It divides bandwidth into multiple orthogonal subcarriers.
记忆口诀
**O**FDM = **O**n **D**igital **M**odes (think 'OFDM = ODM')
实际应用示例
You're using a digital voice mode that employs OFDM. The signal is divided into multiple orthogonal subcarriers, each carrying part of the digital data. This allows efficient, reliable digital communication. OFDM is used in various amateur digital modes because it handles multipath and interference well.
错误选项分析
Option B: Incorrect. OFDM isn't specifically for extremely low-power contacts. It's a general digital modulation technique used in various applications. Option C: Incorrect. OFDM isn't specifically for EME (Earth-Moon-Earth) communications. EME can use various modes, but OFDM isn't specifically an EME technique. Option D: Incorrect. OFDM signals are allowed on amateur bands. They're used in various digital modes and are a legitimate modulation technique.
知识点
OFDM, Digital modes, Orthogonal frequency-division multiplexing, Digital modulation
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.