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T0C10

SAFETY · RF hazards: radiation exposure, proximity to antennas, recognized safe power levels, radiation types, duty cycle

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Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?

  1. AIt affects the average exposure to radiation
  2. BIt affects the peak exposure to radiation
  3. CIt takes into account the antenna feed line loss
  4. DIt takes into account the thermal effects of the final amplifier
Why RF exposure limits are based on power density averaged over a time period (6 minutes for controlled exposure, 30 minutes for uncontrolled), not on instantaneous peaks. Duty cycle is the fraction of that time you are actually transmitting at full power, so a mode like SSB or CW, or intermittent operating, lowers the average exposure compared to continuous-carrier modes like FM or many digital modes. That is why the exposure evaluation lets you scale your transmitter power by the duty cycle when computing average exposure.
Watch out Peak exposure is set by your peak transmitted power and distance, and does not change with how often you key up; duty cycle only affects the time-averaged value. Feed line loss and amplifier heating are separate issues and are not what duty cycle accounts for in an exposure evaluation.
Duty cycle = how much of the time you transmit, so it scales the AVERAGE, not the peak. Averaging times: 6 min controlled, 30 min uncontrolled.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of T0C

  1. T0C01 What type of radiation are radio signals?
  2. T0C02 Which of the following bands has the lowest maximum permissible exposure for RF safety?
  3. T0C03 How does the allowable power density for RF safety change if duty cycle changes from 100 percent to 50 percen…
  4. T0C04 What factors affect the RF exposure of people near an amateur station antenna?
  5. T0C05 Why do exposure limits vary with frequency?
  6. T0C06 Which of the following is an acceptable method to determine whether your station complies with FCC RF exposur…
  7. T0C07 What hazard is created by touching an antenna during a transmission?
  8. T0C08 Which of the following actions can reduce exposure to RF radiation?
  9. T0C09 How can you make sure your station stays in compliance with RF safety regulations?
  10. T0C10 Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?
  11. T0C11 What is the definition of duty cycle during the averaging time for RF exposure?
  12. T0C12 How does RF radiation differ from ionizing radiation (radioactivity)?
  13. T0C13 Who is responsible for ensuring that no person is exposed to RF energy above the FCC exposure limits?
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