Why is it not legal to transmit a 3 kHz bandwidth USB signal with a carrier frequency of 14.348 MHz?
The correct answer is D: The upper 1 kHz of the signal is outside the 20-meter band. Why it is not legal to transmit a 3 kHz bandwidth USB signal with a carrier frequency of 14.348 MHz is that the upper 1 kHz of the signal is outside the 20-meter band. 20-meter band ends at 14.350 MHz; 14.348 + 1.5 kHz (half bandwidth) = 14.3495 MHz is OK, but the upper sideband extends to 14.348 + 3 kHz = 14.351 MHz, which exceeds 14.350 MHz. For amateur radio operators, this is important for band compliance. Understanding this helps ensure legal operation.
Exam Tip
3 kHz USB at 14.348 MHz = upper 1 kHz outside 20m band. Think 'U'pper 'S'ideband = 'U'pper 'S'ignal exceeds band edge. 20m ends at 14.350 MHz; 14.348 + 3 kHz = 14.351 MHz exceeds band. Not USB usage, not lower sideband, not carrier - just upper sideband exceeds band.
Memory Aid
"3 kHz USB at 14.348 MHz = upper 1 kHz outside 20m band. Think 'U'pper 'S'ideband = 'E'xceeds band. 20m ends at 14.350 MHz; upper sideband extends to 14.351 MHz. Important for band compliance."
Real-World Application
A 3 kHz bandwidth USB signal with carrier at 14.348 MHz: The upper sideband extends to 14.348 + 3 kHz = 14.351 MHz. The 20-meter band ends at 14.350 MHz, so the upper 1 kHz (14.350-14.351 MHz) is outside the band. This makes the transmission illegal - the upper sideband exceeds the band edge. This is why it's not legal.
FCC Part 97.301Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. USB is used on 20-meter phone - USB is legal on 20m. USB usage isn't the problem.
Option B: Incorrect. Lower 1 kHz isn't outside the band - 14.348 - 1.5 kHz = 14.3465 MHz is within band. Lower sideband is OK.
Option C: Incorrect. 14.348 MHz isn't outside the band - 20m phone band is 14.225-14.350 MHz, so 14.348 is within band. Carrier frequency is OK.
题目解析
The correct answer is D: The upper 1 kHz of the signal is outside the 20-meter band. Why it is not legal to transmit a 3 kHz bandwidth USB signal with a carrier frequency of 14.348 MHz is that the upper 1 kHz of the signal is outside the 20-meter band. 20-meter band ends at 14.350 MHz; 14.348 + 1.5 kHz (half bandwidth) = 14.3495 MHz is OK, but the upper sideband extends to 14.348 + 3 kHz = 14.351 MHz, which exceeds 14.350 MHz. For amateur radio operators, this is important for band compliance. Understanding this helps ensure legal operation.
考试技巧
3 kHz USB at 14.348 MHz = upper 1 kHz outside 20m band. Think 'U'pper 'S'ideband = 'U'pper 'S'ignal exceeds band edge. 20m ends at 14.350 MHz; 14.348 + 3 kHz = 14.351 MHz exceeds band. Not USB usage, not lower sideband, not carrier - just upper sideband exceeds band.
记忆口诀
3 kHz USB at 14.348 MHz = upper 1 kHz outside 20m band. Think 'U'pper 'S'ideband = 'E'xceeds band. 20m ends at 14.350 MHz; upper sideband extends to 14.351 MHz. Important for band compliance.
实际应用示例
A 3 kHz bandwidth USB signal with carrier at 14.348 MHz: The upper sideband extends to 14.348 + 3 kHz = 14.351 MHz. The 20-meter band ends at 14.350 MHz, so the upper 1 kHz (14.350-14.351 MHz) is outside the band. This makes the transmission illegal - the upper sideband exceeds the band edge. This is why it's not legal.
错误选项分析
Option A: Incorrect. USB is used on 20-meter phone - USB is legal on 20m. USB usage isn't the problem. Option B: Incorrect. Lower 1 kHz isn't outside the band - 14.348 - 1.5 kHz = 14.3465 MHz is within band. Lower sideband is OK. Option C: Incorrect. 14.348 MHz isn't outside the band - 20m phone band is 14.225-14.350 MHz, so 14.348 is within band. Carrier frequency is OK.
知识点
USB signal, 3 kHz bandwidth, 14.348 MHz carrier, 20-meter band edge
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.