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T8A05

SIGNALS AND EMISSIONS · Basic characteristics of FM and SSB; Bandwidth of various modulation modes: CW, SSB, FM, fast-scan TV; Choice of emission type: selection of USB vs LSB, use of SSB for weak signal work, use of FM for VHF packet and repeaters

T8A05T8A →

Which of the following signal types has the narrowest bandwidth?

  1. AFM voice
  2. BSSB voice
  3. CCW
  4. DSlow-scan TV
Why Bandwidth grows with how much information the signal carries. CW is just an on/off keyed carrier sent at a few dozen words per minute, so it only needs roughly 100 to 300 Hz. SSB voice needs about 2 to 3 kHz to pass speech frequencies, slow-scan TV occupies a similar voice-sized channel because it is audio tones, and FM voice spreads out to 10 to 15 kHz because of the frequency deviation plus sidebands.
Watch out SSB voice is the narrowest of the voice modes, which makes it tempting, but at about 3 kHz it is still ten or more times wider than keyed CW.
Bandwidth ladder: CW (~150 Hz) < SSB/SSTV (~3 kHz) < FM (~10-15 kHz) < fast-scan TV (MHz).
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of T8A

  1. T8A01 Which of the following is a form of amplitude modulation?
  2. T8A02 What type of modulation is commonly used for VHF packet radio transmissions?
  3. T8A03 Which type of voice mode is often used for long-distance (weak signal) contacts on the VHF and UHF bands?
  4. T8A04 Which type of modulation is commonly used for VHF and UHF voice repeaters?
  5. T8A05 Which of the following signal types has the narrowest bandwidth?
  6. T8A06 Which sideband is normally used for 10-meter HF, VHF, and UHF single-sideband communications?
  7. T8A07 What is one characteristic of single sideband (SSB) compared to FM?
  8. T8A08 What is the approximate bandwidth of a typical single sideband (SSB) voice signal?
  9. T8A09 What is the approximate bandwidth of an FM voice signal on VHF repeaters?
  10. T8A10 What is the approximate bandwidth of AM fast-scan TV transmissions?
  11. T8A11 What is the approximate bandwidth required to transmit a CW signal?
  12. T8A12 Which of the following is a disadvantage of FM compared with single sideband?
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