Question T8A05
From subelement T8 - T8A
Which of the following types of signal has the narrowest bandwidth?
Why is this correct?
CW (Morse code) has the narrowest bandwidth at approximately 150 Hz. FM voice requires 10-15 kHz, SSB voice needs about 3 kHz, and slow-scan TV uses several kHz. CW's extreme efficiency comes from transmitting simple on/off pulses rather than complex audio or video information, allowing many more CW signals to fit in the same frequency space.
Memory tip
Think bandwidth hierarchy: CW < SSB < FM < TV modes. More complex information requires more frequency space. This pattern helps you rank any signal types by information complexity—simple pulses need less spectrum than voice, which needs less than video.
Learn more
CW's narrow 150 Hz bandwidth makes it invaluable for weak signal work and crowded band conditions. This efficiency explains why Part 97 grants CW emission privileges across all amateur bands, including narrow HF segments where wider modes wouldn't fit. Understanding bandwidth requirements helps you choose appropriate modes for band plans and operating conditions—critical for spectrum management and interference avoidance.
Think about it
Why do you think CW remains popular for weak signal communication and emergency operations despite requiring operators to learn Morse code?