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Subel. E0
12 questions
Subelement E0

SAFETY

Section E0A

Safety: RF radiation hazards; hazardous materials; grounding

What is the primary function of an external earth connection or ground rod?

  • Prevent static build up on power lines
  • Correct Answer
    Lightning charge dissipation
  • Reduce RF current flow between pieces of equipment
  • Protect breaker panel from power surges

There are some benefits to any common ground for all of the provided options, but the key here is that it is specifically an "external earth connection or ground rod" -- in other words, this ground is actually going into the ground outside, not just into a common terminal which has been dubbed "ground" or into the house "ground".

The main reason to do that is that in the case of a lightning strike the current will take the path of least resistance to get to earth ground and you want that path to be both as short as possible and to get there much more easily than it can get to your equipment.

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When evaluating RF exposure levels from your station at a neighbor’s home, what must you do?

  • Ensure signals from your station are less than the controlled maximum permissible exposure (MPE) limits
  • Correct Answer
    Ensure signals from your station are less than the uncontrolled maximum permissible exposure (MPE) limits
  • Ensure signals from your station are less than the controlled maximum permissible emission (MPE) limits
  • Ensure signals from your station are less than the uncontrolled maximum permissible emission (MPE) limits

The two sets of exposure limits are controlled and uncontrolled. If you don't have the ability to restrict access to the area of exposure, then you must use the uncontrolled exposure limits.

In this case, you can't control where your neighbor is nor prevent him/her from being in an area of exposure, hence, you must use the uncontrolled MPE (Maximum Permissible Exposure) limits.

Hint: Don't be fooled by answers with Emission in them. Exposure is the word used in this question.

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Over what range of frequencies are the FCC human body RF exposure limits most restrictive?

  • 300 kHz - 3 MHz
  • 3 - 30 MHz
  • Correct Answer
    30 - 300 MHz
  • 300 - 3000 MHz

FCC human body RF exposure limits are most restrictive for those frequencies where the human body may present a resonant wavelength. This is where the maximum absorption might occur.

The average height of a human male is 5' 9" or 1.75 meters. For females this is 5' 4" or 1.6 meters. This corresponds to a full wavelength of 171 to 188 MHz and a half wavelength of 85 to 94 MHz. These frequencies fall in the range of 30-300MHz.

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When evaluating a site with multiple transmitters operating at the same time, the operators and licensees of which transmitters are responsible for mitigating over-exposure situations?

  • Each transmitter that produces 20 percent or more of its MPE limit in areas where the total MPE limit is exceeded
  • Each transmitter operating with a duty cycle greater than 25 percent
  • Correct Answer
    Each transmitter that produces 5 percent or more of its MPE limit in areas where the total MPE limit is exceeded
  • Each transmitter operating with a duty cycle greater than 50 percent

This is an FCC rule designed to avoid arguments. In essence, any station that provides a significant portion of the transmitted power is responsible to ensure exposure limits are met.

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What hazard is created by operating at microwave frequencies?

  • Microwaves are ionizing radiation
  • Correct Answer
    The high gain antennas commonly used can result in high exposure levels
  • Microwaves are in the frequency range where wave velocity is higher
  • The extremely high frequency energy can damage the joints of antenna structures

In the microwave range, the wavelengths are fairly small. This allows easy, inexpensive construction of high-gain antennas. The small size of the antenna can be deceptive relative to the high field strength it can generate. Caution must be used to protect people when using these antennas.

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Why are there separate electric (E) and magnetic (H) MPE limits at frequencies below 300 MHz?

  • The body reacts to electromagnetic radiation from both the E and H fields
  • Ground reflections and scattering cause the field strength to vary with location
  • E field and H field radiation intensity peaks can occur at different locations
  • Correct Answer
    All these choices are correct

All of these are correct and should be accounted for when considering Maximum Permissible Exposure (MPE) limits.

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What is meant by “100% tie-off” regarding tower safety?

  • All loose ropes and guys secured to a fixed structure
  • Correct Answer
    At least one lanyard attached to the tower at all times
  • All tools secured to the climber’s harness
  • All circuit breakers feeding power to the tower must be tied closed with tape, cable, or ties
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What does SAR measure?

  • Signal attenuation ratio
  • Signal amplification rating
  • Correct Answer
    The rate at which RF energy is absorbed by the body
  • The rate of RF energy reflected from stationary terrain

SAR, in this case, stands for Specific Absorption Rate. This is the rate at which the human body absorbs energy from an electromagnetic field. The SAR is affected by both frequency and body part.

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Which of the following types of equipment are exempt from RF exposure evaluations?

  • Transceivers with less than 7 watts of RF output
  • Antennas that radiate only in the near field
  • Correct Answer
    Hand-held transceivers sold before May 3, 2021
  • Dish antennas less than one meter in diameter
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When must an RF exposure evaluation be performed on an amateur station operating on 80 meters?

  • Correct Answer
    An evaluation must always be performed
  • When the ERP of the station is less than 10 watts
  • When the station’s operating mode is CW
  • When the output power from the transmitter is less than 100 watts
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To what should lanyards be attached while climbing?

  • Antenna mast
  • Guy brackets
  • Tower rungs
  • Correct Answer
    Tower legs
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Where should a shock-absorbing lanyard be attached to a tower when working above ground?

  • Correct Answer
    Above the climber’s head level
  • To the belt of the fall-arrest harness
  • Even with the climber's waist
  • To the next lowest set of guys
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