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E4E06

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

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What type of electrical interference can be caused by computer network equipment?

  1. AA loud AC hum in the audio output of your station's receiver
  2. BA clicking noise at intervals of a few seconds
  3. CThe appearance of unstable modulated or unmodulated signals at specific frequencies
  4. DA whining-type noise that continually pulses off and on
Why Computer and network gear runs on crystal-controlled clock oscillators, and those clocks (plus their harmonics and the data streams riding on Ethernet cables) radiate as discrete carriers landing on specific, repeatable frequencies. On the air they show up as birdies that may be bare carriers or may be smeared and modulated by the data traffic, and they can drift or come and go as the equipment's clocks and load change. Switching power supplies in the same equipment add to the harmonic comb.
Watch out A loud AC hum points to a power supply or ground problem at 60/120 Hz, the clicking every few seconds is the classic electric fence charger signature, and a pulsing whine is typical of a vehicle alternator or a variable-speed motor, none of which are clock-derived.
Digital clocks make birdies: network gear gives signals on specific frequencies, not hum, clicks or whine.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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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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