What describes orthogonal frequency-division multiplexing (OFDM)?
The correct answer is D: A digital modulation technique using subcarriers at frequencies chosen to avoid intersymbol interference. Orthogonal frequency-division multiplexing (OFDM) is a digital modulation technique using subcarriers at frequencies chosen to avoid intersymbol interference. The subcarriers are spaced so they're orthogonal (mathematically independent), preventing interference between them.
OFDM divides the available bandwidth into many narrow subcarriers, each carrying part of the data. The subcarrier frequencies are chosen so they're orthogonal - the peak of one subcarrier aligns with the nulls of adjacent subcarriers, preventing intersymbol interference. This allows efficient use of bandwidth and makes OFDM resistant to multipath fading. OFDM is used in many modern digital communication systems including Wi-Fi, digital TV, and amateur digital modes.
Exam Tip
OFDM = Digital modulation with orthogonal subcarriers. Remember: OFDM is a digital modulation technique using subcarriers at frequencies chosen to avoid intersymbol interference. The subcarriers are orthogonal.
Memory Aid
"**O**FDM = **O**rthogonal **S**ubcarriers **A**void **I**nterference (think 'OFDM = OSAI')"
Real-World Application
You're using an OFDM digital mode. The signal is divided into multiple subcarriers, each at a specific frequency. These frequencies are chosen so the subcarriers are orthogonal - they don't interfere with each other. This allows multiple data streams to be transmitted simultaneously without intersymbol interference, making efficient use of bandwidth.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. OFDM isn't a frequency modulation technique. It's a digital modulation technique that uses multiple subcarriers, not FM.
Option B: Incorrect. OFDM isn't specifically a bandwidth compression technique. It's a multiplexing technique that divides bandwidth into subcarriers.
Option C: Incorrect. OFDM can be used for high-speed transmissions, not just narrow-band, slow-speed. It's used in many high-speed digital systems.
题目解析
The correct answer is D: A digital modulation technique using subcarriers at frequencies chosen to avoid intersymbol interference. Orthogonal frequency-division multiplexing (OFDM) is a digital modulation technique using subcarriers at frequencies chosen to avoid intersymbol interference. The subcarriers are spaced so they're orthogonal (mathematically independent), preventing interference between them. OFDM divides the available bandwidth into many narrow subcarriers, each carrying part of the data. The subcarrier frequencies are chosen so they're orthogonal - the peak of one subcarrier aligns with the nulls of adjacent subcarriers, preventing intersymbol interference. This allows efficient use of bandwidth and makes OFDM resistant to multipath fading. OFDM is used in many modern digital communication systems including Wi-Fi, digital TV, and amateur digital modes.
考试技巧
OFDM = Digital modulation with orthogonal subcarriers. Remember: OFDM is a digital modulation technique using subcarriers at frequencies chosen to avoid intersymbol interference. The subcarriers are orthogonal.
记忆口诀
**O**FDM = **O**rthogonal **S**ubcarriers **A**void **I**nterference (think 'OFDM = OSAI')
实际应用示例
You're using an OFDM digital mode. The signal is divided into multiple subcarriers, each at a specific frequency. These frequencies are chosen so the subcarriers are orthogonal - they don't interfere with each other. This allows multiple data streams to be transmitted simultaneously without intersymbol interference, making efficient use of bandwidth.
错误选项分析
Option A: Incorrect. OFDM isn't a frequency modulation technique. It's a digital modulation technique that uses multiple subcarriers, not FM. Option B: Incorrect. OFDM isn't specifically a bandwidth compression technique. It's a multiplexing technique that divides bandwidth into subcarriers. Option C: Incorrect. OFDM can be used for high-speed transmissions, not just narrow-band, slow-speed. It's used in many high-speed digital systems.
知识点
OFDM, Digital modulation, Subcarriers, Orthogonal frequencies, Intersymbol interference
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.