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E4E01

AMATEUR PRACTICES · Noise and interference: external RF interference; electrical and computer noise; line noise; DSP filtering and noise reduction; common-mode current; surge protectors; single point ground panel

E4E01E4E →

What problem can occur when using an automatic notch filter (ANF) to remove interfering carriers while receiving CW signals?

  1. ARemoval of the CW signal as well as the interfering carrier
  2. BAny nearby signal passing through the DSP system will overwhelm the desired signal
  3. CExcessive ringing
  4. DAll these choices are correct
Why An automatic notch filter works by detecting any steady, narrow-band tone in the passband and adaptively placing a notch on it. A CW signal is itself a steady single tone, so the DSP cannot distinguish the desired Morse carrier from an unwanted heterodyne and may notch out both. That is why ANF is normally used on SSB/AM voice and turned off for CW, where a narrow bandpass filter or manual notch is the better tool.
Watch out Excessive ringing is a real DSP artifact, but it comes from very narrow, steep-skirted bandpass filters, not from the automatic notch function; and a strong nearby signal overloading the receiver is a front-end dynamic range issue, not an ANF behavior.
ANF hunts steady tones, and CW is a steady tone. Turn ANF off for CW.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
All of E4E E4E02 →

The rest of E4E

  1. E4E01 What problem can occur when using an automatic notch filter (ANF) to remove interfering carriers while receiv…
  2. E4E02 Which of the following types of noise can often be reduced by a digital noise reduction?
  3. E4E03 Which of the following types of noise are removed by a noise blanker?
  4. E4E04 How can conducted noise from an automobile battery charging system be suppressed?
  5. E4E05 What is used to suppress radio frequency interference from a line-driven AC motor?
  6. E4E06 What type of electrical interference can be caused by computer network equipment?
  7. E4E07 Which of the following can cause shielded cables to radiate or receive interference?
  8. E4E08 What current flows equally on all conductors of an unshielded multiconductor cable?
  9. E4E09 What undesirable effect can occur when using a noise blanker?
  10. E4E10 Which of the following can create intermittent loud roaring or buzzing AC line interference?
  11. E4E11 What could be the cause of local AM broadcast band signals combining to generate spurious signals on the MF o…
  12. E4E12 What causes interference received as a series of carriers at regular intervals across a wide frequency range?
  13. E4E13 Where should a station AC surge protector be installed?
  14. E4E14 What is the purpose of a single point ground panel?
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