Which type of modulation is commonly used for VHF and UHF voice repeaters?
The correct answer is D: FM or PM. FM (Frequency Modulation) or PM (Phase Modulation) is commonly used for VHF and UHF voice repeaters. FM is the standard for repeater operation because it provides good audio quality, is less affected by noise, has a capture effect (stronger signal captures the receiver), and works well with the wide bandwidth available on VHF/UHF. For amateur radio operators, virtually all VHF/UHF repeaters use FM, making it the primary mode for local and regional communications. Understanding this helps when selecting equipment and understanding repeater operations.
Exam Tip
VHF/UHF repeaters = FM or PM. Think 'R'epeaters = 'R'egular 'F'M. FM is the standard for voice repeaters because of good audio quality, noise immunity, and capture effect. AM, SSB, and PSK are used for other applications.
Memory Aid
"VHF/UHF repeaters = FM or PM. Think 'R'epeaters = 'R'egular 'F'M. Standard for voice repeaters due to good audio quality and noise immunity. Most common mode for local communications."
Real-World Application
Your local 2-meter repeater uses FM. When you transmit on the input frequency (146.34 MHz), the repeater receives your FM signal and retransmits it on the output frequency (146.94 MHz), also using FM. This provides clear audio and reliable communications. FM's capture effect means if two signals are received, the stronger one is heard, preventing interference from weak signals.
Key Concepts
Why Other Options Are Wrong
Option A (AM): Incorrect. AM is not commonly used for VHF/UHF repeaters. It's less efficient and more susceptible to noise than FM.
Option B (SSB): Incorrect. SSB is used for weak-signal work on VHF/UHF but not for repeaters. Repeaters use FM for better audio quality and simpler operation.
Option C (PSK): Incorrect. PSK is a digital modulation mode, not used for voice repeaters. Voice repeaters use analog FM.
题目解析
The correct answer is D: FM or PM. FM (Frequency Modulation) or PM (Phase Modulation) is commonly used for VHF and UHF voice repeaters. FM is the standard for repeater operation because it provides good audio quality, is less affected by noise, has a capture effect (stronger signal captures the receiver), and works well with the wide bandwidth available on VHF/UHF. For amateur radio operators, virtually all VHF/UHF repeaters use FM, making it the primary mode for local and regional communications. Understanding this helps when selecting equipment and understanding repeater operations.
考试技巧
VHF/UHF repeaters = FM or PM. Think 'R'epeaters = 'R'egular 'F'M. FM is the standard for voice repeaters because of good audio quality, noise immunity, and capture effect. AM, SSB, and PSK are used for other applications.
记忆口诀
VHF/UHF repeaters = FM or PM. Think 'R'epeaters = 'R'egular 'F'M. Standard for voice repeaters due to good audio quality and noise immunity. Most common mode for local communications.
实际应用示例
Your local 2-meter repeater uses FM. When you transmit on the input frequency (146.34 MHz), the repeater receives your FM signal and retransmits it on the output frequency (146.94 MHz), also using FM. This provides clear audio and reliable communications. FM's capture effect means if two signals are received, the stronger one is heard, preventing interference from weak signals.
错误选项分析
Option A (AM): Incorrect. AM is not commonly used for VHF/UHF repeaters. It's less efficient and more susceptible to noise than FM. Option B (SSB): Incorrect. SSB is used for weak-signal work on VHF/UHF but not for repeaters. Repeaters use FM for better audio quality and simpler operation. Option C (PSK): Incorrect. PSK is a digital modulation mode, not used for voice repeaters. Voice repeaters use analog FM.
知识点
FM repeaters, VHF/UHF repeaters, Repeater operation, Voice communications
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.