What is the approximate bandwidth of a VHF repeater FM voice signal?
The correct answer is C: Between 10 and 15 kHz. The approximate bandwidth of a VHF repeater FM voice signal is between 10 and 15 kHz. FM requires wider bandwidth than SSB because the frequency deviation (typically ±5 kHz for narrowband FM) plus the audio bandwidth creates a total bandwidth of about 12-15 kHz. For amateur radio operators, understanding FM bandwidth helps explain why FM uses more spectrum than SSB and why fewer FM signals can fit in a given frequency range. The wider bandwidth provides good audio quality and noise immunity.
Exam Tip
VHF FM repeater = 10-15 kHz bandwidth. Think 'F'M = 'F'requency 'M'odulation = 'F'airly wide (~12-15 kHz). Narrowband FM uses ±5 kHz deviation, creating 10-15 kHz total bandwidth. Much wider than SSB (3 kHz) or CW (150 Hz).
Memory Aid
"VHF FM repeater = 10-15 kHz bandwidth. Think 'F'M = 'F'requency 'M'odulation = 'F'airly wide (~12-15 kHz). Narrowband FM with ±5 kHz deviation creates 10-15 kHz total bandwidth."
Real-World Application
Your 2-meter FM repeater signal uses about 12-15 kHz of bandwidth. The ±5 kHz frequency deviation plus the audio frequencies create this bandwidth. This is why FM repeaters need more spacing between channels than SSB - each FM signal needs about 15 kHz, while SSB needs only 3 kHz. The wider bandwidth provides good audio quality and noise immunity.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Less than 500 Hz is way too narrow - that's CW bandwidth. FM needs much more bandwidth for the frequency deviation and audio.
Option B: Incorrect. About 150 kHz is far too wide - that's more than 10 times the actual FM bandwidth. FM uses about 12-15 kHz.
Option D: Incorrect. Between 50 and 125 kHz is far too wide - that's wideband FM used in broadcasting, not narrowband FM used in amateur repeaters.
题目解析
The correct answer is C: Between 10 and 15 kHz. The approximate bandwidth of a VHF repeater FM voice signal is between 10 and 15 kHz. FM requires wider bandwidth than SSB because the frequency deviation (typically ±5 kHz for narrowband FM) plus the audio bandwidth creates a total bandwidth of about 12-15 kHz. For amateur radio operators, understanding FM bandwidth helps explain why FM uses more spectrum than SSB and why fewer FM signals can fit in a given frequency range. The wider bandwidth provides good audio quality and noise immunity.
考试技巧
VHF FM repeater = 10-15 kHz bandwidth. Think 'F'M = 'F'requency 'M'odulation = 'F'airly wide (~12-15 kHz). Narrowband FM uses ±5 kHz deviation, creating 10-15 kHz total bandwidth. Much wider than SSB (3 kHz) or CW (150 Hz).
记忆口诀
VHF FM repeater = 10-15 kHz bandwidth. Think 'F'M = 'F'requency 'M'odulation = 'F'airly wide (~12-15 kHz). Narrowband FM with ±5 kHz deviation creates 10-15 kHz total bandwidth.
实际应用示例
Your 2-meter FM repeater signal uses about 12-15 kHz of bandwidth. The ±5 kHz frequency deviation plus the audio frequencies create this bandwidth. This is why FM repeaters need more spacing between channels than SSB - each FM signal needs about 15 kHz, while SSB needs only 3 kHz. The wider bandwidth provides good audio quality and noise immunity.
错误选项分析
Option A: Incorrect. Less than 500 Hz is way too narrow - that's CW bandwidth. FM needs much more bandwidth for the frequency deviation and audio. Option B: Incorrect. About 150 kHz is far too wide - that's more than 10 times the actual FM bandwidth. FM uses about 12-15 kHz. Option D: Incorrect. Between 50 and 125 kHz is far too wide - that's wideband FM used in broadcasting, not narrowband FM used in amateur repeaters.
知识点
FM bandwidth, VHF repeaters, Frequency deviation, Voice bandwidth
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.