What spread spectrum communications technique uses a high-speed binary bit stream to shift the phase of an RF carrier?
The correct answer is B: Direct sequence. Direct sequence spread spectrum is the technique that uses a high-speed binary bit stream to shift the phase of an RF carrier. The binary stream (spreading code) directly modulates the carrier phase, spreading the signal across a wide bandwidth.
In direct sequence spread spectrum (DSSS), a high-speed pseudorandom binary sequence (the spreading code) is used to phase-shift the carrier. This spreads the signal energy across a wide frequency band. The receiver uses the same code to despread the signal. DSSS is widely used in systems like Wi-Fi (802.11b), GPS, and some amateur spread spectrum modes. The high-speed code creates the wide bandwidth characteristic of spread spectrum signals.
Exam Tip
Direct sequence = Binary stream shifts phase. Remember: Direct sequence spread spectrum uses a high-speed binary bit stream to shift the phase of an RF carrier, spreading the signal across a wide bandwidth.
Memory Aid
"**D**irect **S**equence = **B**inary **S**tream **P**hase **S**hift (think 'DS = BSPS')"
Real-World Application
You're using a direct sequence spread spectrum system. A high-speed pseudorandom binary sequence (maybe millions of bits per second) phase-shifts your RF carrier. This spreads your signal energy across a wide frequency band. At the receiver, the same code is used to despread the signal, recovering the original narrow-band information.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Frequency hopping rapidly changes the carrier frequency, not the phase. It doesn't use a binary bit stream to shift phase.
Option C: Incorrect. Binary phase-shift keying (BPSK) is a modulation method, not a spread spectrum technique. DSSS uses BPSK as part of its operation, but the spread spectrum technique itself is direct sequence.
Option D: Incorrect. Phase compandored spread spectrum isn't a standard term. Direct sequence is the correct answer.
题目解析
The correct answer is B: Direct sequence. Direct sequence spread spectrum is the technique that uses a high-speed binary bit stream to shift the phase of an RF carrier. The binary stream (spreading code) directly modulates the carrier phase, spreading the signal across a wide bandwidth. In direct sequence spread spectrum (DSSS), a high-speed pseudorandom binary sequence (the spreading code) is used to phase-shift the carrier. This spreads the signal energy across a wide frequency band. The receiver uses the same code to despread the signal. DSSS is widely used in systems like Wi-Fi (802.11b), GPS, and some amateur spread spectrum modes. The high-speed code creates the wide bandwidth characteristic of spread spectrum signals.
考试技巧
Direct sequence = Binary stream shifts phase. Remember: Direct sequence spread spectrum uses a high-speed binary bit stream to shift the phase of an RF carrier, spreading the signal across a wide bandwidth.
记忆口诀
**D**irect **S**equence = **B**inary **S**tream **P**hase **S**hift (think 'DS = BSPS')
实际应用示例
You're using a direct sequence spread spectrum system. A high-speed pseudorandom binary sequence (maybe millions of bits per second) phase-shifts your RF carrier. This spreads your signal energy across a wide frequency band. At the receiver, the same code is used to despread the signal, recovering the original narrow-band information.
错误选项分析
Option A: Incorrect. Frequency hopping rapidly changes the carrier frequency, not the phase. It doesn't use a binary bit stream to shift phase. Option C: Incorrect. Binary phase-shift keying (BPSK) is a modulation method, not a spread spectrum technique. DSSS uses BPSK as part of its operation, but the spread spectrum technique itself is direct sequence. Option D: Incorrect. Phase compandored spread spectrum isn't a standard term. Direct sequence is the correct answer.
知识点
Direct sequence, Spread spectrum, Phase shifting, Binary bit stream
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.