Which type of voice mode is often used for long-distance (weak signal) contacts on the VHF and UHF bands?
The correct answer is C: SSB. Single sideband (SSB) is often used for long-distance (weak signal) contacts on VHF and UHF bands. SSB is more efficient than FM for weak-signal work because it uses less bandwidth (about 3 kHz vs 15 kHz for FM) and puts all power into the information-carrying sideband. This makes SSB better for weak-signal propagation modes like tropospheric ducting, sporadic E, and meteor scatter. For amateur radio operators, SSB on VHF/UHF is essential for weak-signal work, DX, and contesting where maximum efficiency is needed.
Exam Tip
VHF/UHF weak-signal = SSB. Think 'W'eak 'S'ignal = 'W'orks with 'S'SB. SSB is more efficient (narrower bandwidth, all power in sideband) making it better for weak-signal and long-distance contacts than FM.
Memory Aid
"VHF/UHF weak-signal = SSB. Think 'W'eak 'S'ignal = 'W'orks with 'S'SB. More efficient than FM for long-distance weak-signal contacts. Narrow bandwidth and efficient power use."
Real-World Application
During a sporadic E opening on 6 meters, operators use SSB for weak-signal contacts hundreds of miles away. SSB's narrow bandwidth (3 kHz) and efficient use of power make it possible to copy signals that would be inaudible on FM. The same signal that's readable on SSB might be completely lost in the noise on FM due to FM's wider bandwidth and capture effect.
Key Concepts
Why Other Options Are Wrong
Option A (FM): Incorrect. FM is used for local communications and repeaters but is less efficient for weak-signal work. SSB is better for long-distance weak-signal contacts.
Option B (DRM): Incorrect. DRM (Digital Radio Mondiale) is a digital broadcasting system, not commonly used for amateur VHF/UHF weak-signal work.
Option D (PM): Incorrect. Phase modulation is similar to FM but not commonly used for VHF/UHF weak-signal work. SSB is the standard.
题目解析
The correct answer is C: SSB. Single sideband (SSB) is often used for long-distance (weak signal) contacts on VHF and UHF bands. SSB is more efficient than FM for weak-signal work because it uses less bandwidth (about 3 kHz vs 15 kHz for FM) and puts all power into the information-carrying sideband. This makes SSB better for weak-signal propagation modes like tropospheric ducting, sporadic E, and meteor scatter. For amateur radio operators, SSB on VHF/UHF is essential for weak-signal work, DX, and contesting where maximum efficiency is needed.
考试技巧
VHF/UHF weak-signal = SSB. Think 'W'eak 'S'ignal = 'W'orks with 'S'SB. SSB is more efficient (narrower bandwidth, all power in sideband) making it better for weak-signal and long-distance contacts than FM.
记忆口诀
VHF/UHF weak-signal = SSB. Think 'W'eak 'S'ignal = 'W'orks with 'S'SB. More efficient than FM for long-distance weak-signal contacts. Narrow bandwidth and efficient power use.
实际应用示例
During a sporadic E opening on 6 meters, operators use SSB for weak-signal contacts hundreds of miles away. SSB's narrow bandwidth (3 kHz) and efficient use of power make it possible to copy signals that would be inaudible on FM. The same signal that's readable on SSB might be completely lost in the noise on FM due to FM's wider bandwidth and capture effect.
错误选项分析
Option A (FM): Incorrect. FM is used for local communications and repeaters but is less efficient for weak-signal work. SSB is better for long-distance weak-signal contacts. Option B (DRM): Incorrect. DRM (Digital Radio Mondiale) is a digital broadcasting system, not commonly used for amateur VHF/UHF weak-signal work. Option D (PM): Incorrect. Phase modulation is similar to FM but not commonly used for VHF/UHF weak-signal work. SSB is the standard.
知识点
SSB on VHF/UHF, Weak signal operation, Long-distance contacts, VHF/UHF SSB
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.