Which describes spread spectrum frequency hopping?
The correct answer is D: Rapidly varying the frequency of a transmitted signal according to a pseudorandom sequence. Spread spectrum frequency hopping is rapidly varying the frequency of a transmitted signal according to a pseudorandom sequence. The carrier frequency hops from one frequency to another in a pseudorandom pattern.
In frequency hopping spread spectrum (FHSS), the transmitter and receiver follow the same pseudorandom frequency-hopping pattern. The signal rapidly jumps between different frequencies according to this pattern. Both transmitter and receiver must be synchronized to the same hopping sequence. FHSS is used in systems like Bluetooth and some military communications. The rapid frequency changes make the signal resistant to interference and difficult to intercept without knowing the hopping pattern.
Exam Tip
Frequency hopping = Rapidly vary frequency pseudorandomly. Remember: Frequency hopping spread spectrum rapidly varies the frequency of a transmitted signal according to a pseudorandom sequence. The carrier hops between frequencies.
Memory Aid
"**F**requency **H**opping = **R**apidly **V**ary **F**requency (think 'FH = RVF')"
Real-World Application
You're using a frequency hopping spread spectrum system. Your transmitter rapidly hops between different frequencies (maybe 1000 hops per second) following a pseudorandom pattern. Your receiver follows the same pattern, hopping in sync. An observer without the pattern sees the signal jumping around randomly, making it resistant to interference and difficult to intercept.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Frequency hopping doesn't involve the receiver signaling the transmitter to change frequencies. Both follow a predetermined pseudorandom sequence automatically.
Option B: Incorrect. Clipping signals to generate harmonics doesn't describe frequency hopping. FHSS changes the carrier frequency, not by generating harmonics.
Option C: Incorrect. A binary bit stream shifting phase describes direct sequence spread spectrum, not frequency hopping. FHSS changes frequency, not phase.
题目解析
The correct answer is D: Rapidly varying the frequency of a transmitted signal according to a pseudorandom sequence. Spread spectrum frequency hopping is rapidly varying the frequency of a transmitted signal according to a pseudorandom sequence. The carrier frequency hops from one frequency to another in a pseudorandom pattern. In frequency hopping spread spectrum (FHSS), the transmitter and receiver follow the same pseudorandom frequency-hopping pattern. The signal rapidly jumps between different frequencies according to this pattern. Both transmitter and receiver must be synchronized to the same hopping sequence. FHSS is used in systems like Bluetooth and some military communications. The rapid frequency changes make the signal resistant to interference and difficult to intercept without knowing the hopping pattern.
考试技巧
Frequency hopping = Rapidly vary frequency pseudorandomly. Remember: Frequency hopping spread spectrum rapidly varies the frequency of a transmitted signal according to a pseudorandom sequence. The carrier hops between frequencies.
记忆口诀
**F**requency **H**opping = **R**apidly **V**ary **F**requency (think 'FH = RVF')
实际应用示例
You're using a frequency hopping spread spectrum system. Your transmitter rapidly hops between different frequencies (maybe 1000 hops per second) following a pseudorandom pattern. Your receiver follows the same pattern, hopping in sync. An observer without the pattern sees the signal jumping around randomly, making it resistant to interference and difficult to intercept.
错误选项分析
Option A: Incorrect. Frequency hopping doesn't involve the receiver signaling the transmitter to change frequencies. Both follow a predetermined pseudorandom sequence automatically. Option B: Incorrect. Clipping signals to generate harmonics doesn't describe frequency hopping. FHSS changes the carrier frequency, not by generating harmonics. Option C: Incorrect. A binary bit stream shifting phase describes direct sequence spread spectrum, not frequency hopping. FHSS changes frequency, not phase.
知识点
Frequency hopping, Spread spectrum, Pseudorandom sequence, Frequency variation
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.