What type of modulation is commonly used for VHF packet radio transmissions?
The correct answer is A: FM or PM. FM (Frequency Modulation) or PM (Phase Modulation) is commonly used for VHF packet radio transmissions. Packet radio on VHF typically uses 1200 or 9600 baud AFSK (Audio Frequency Shift Keying), which is a form of FM. The digital data modulates an audio tone, which then frequency-modulates the RF carrier. For amateur radio operators, FM packet radio is the standard for VHF data communications, used for APRS, bulletin boards, and digital messaging. Understanding this helps when setting up packet radio stations.
Exam Tip
VHF packet radio = FM or PM. Think 'V'HF 'P'acket = 'V'oice band 'F'M. Packet radio on VHF uses FM modulation, typically 1200 or 9600 baud AFSK. SSB, AM, and PSK are used for other applications.
Memory Aid
"VHF packet radio = FM or PM. Think 'V'HF 'P'acket = 'V'oice band 'F'M. Uses frequency modulation for digital data transmission on VHF bands."
Real-World Application
Your VHF packet radio station uses FM modulation. The TNC (Terminal Node Controller) generates audio tones (mark and space) that frequency-modulate your 2-meter transmitter. This FM signal carries the digital packet data. FM is ideal for VHF because it's less affected by noise and works well with the FM repeaters commonly used on VHF.
Key Concepts
Why Other Options Are Wrong
Option B (SSB): Incorrect. SSB is used for voice and some digital modes on HF, but not typically for VHF packet radio. VHF packet uses FM.
Option C (AM): Incorrect. AM is not commonly used for VHF packet radio. FM is the standard for VHF data communications.
Option D (PSK): Incorrect. PSK is a digital modulation mode used on HF, not typically for VHF packet radio. VHF packet uses FM/PM.
题目解析
The correct answer is A: FM or PM. FM (Frequency Modulation) or PM (Phase Modulation) is commonly used for VHF packet radio transmissions. Packet radio on VHF typically uses 1200 or 9600 baud AFSK (Audio Frequency Shift Keying), which is a form of FM. The digital data modulates an audio tone, which then frequency-modulates the RF carrier. For amateur radio operators, FM packet radio is the standard for VHF data communications, used for APRS, bulletin boards, and digital messaging. Understanding this helps when setting up packet radio stations.
考试技巧
VHF packet radio = FM or PM. Think 'V'HF 'P'acket = 'V'oice band 'F'M. Packet radio on VHF uses FM modulation, typically 1200 or 9600 baud AFSK. SSB, AM, and PSK are used for other applications.
记忆口诀
VHF packet radio = FM or PM. Think 'V'HF 'P'acket = 'V'oice band 'F'M. Uses frequency modulation for digital data transmission on VHF bands.
实际应用示例
Your VHF packet radio station uses FM modulation. The TNC (Terminal Node Controller) generates audio tones (mark and space) that frequency-modulate your 2-meter transmitter. This FM signal carries the digital packet data. FM is ideal for VHF because it's less affected by noise and works well with the FM repeaters commonly used on VHF.
错误选项分析
Option B (SSB): Incorrect. SSB is used for voice and some digital modes on HF, but not typically for VHF packet radio. VHF packet uses FM. Option C (AM): Incorrect. AM is not commonly used for VHF packet radio. FM is the standard for VHF data communications. Option D (PSK): Incorrect. PSK is a digital modulation mode used on HF, not typically for VHF packet radio. VHF packet uses FM/PM.
知识点
Packet radio, FM modulation, VHF data, Digital communications
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.