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T8A09

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

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What is the approximate bandwidth of an FM voice signal on VHF repeaters?

  1. ALess than 500 Hz
  2. BAbout 150 kHz
  3. CBetween 10 and 15 kHz
  4. DBetween 50 and 125 kHz
Why Amateur FM on VHF repeaters uses about 5 kHz peak deviation with audio out to roughly 3 kHz, and Carson's rule (bandwidth = 2 x (deviation + highest audio frequency)) gives about 16 kHz, so the usual figure quoted is 10 to 15 kHz. That is why repeater channels are spaced 15 or 20 kHz apart. FM is much wider than SSB voice (about 3 kHz) because the carrier swings back and forth in frequency.
Watch out The choice near 150 kHz describes commercial broadcast FM, which uses much larger deviation and 200 kHz channel spacing; the under 500 Hz figure is a CW signal.
Ham FM fits a 15 kHz repeater channel; broadcast FM needs 150 kHz. Same mode, ten times the room.
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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