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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?
  • Reduce received noise
  • Correct Answer
    Lightning protection
  • Reduce RF current flow between pieces of equipment
  • Reduce RFI to telephones and home entertainment systems

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 Permitted Exposure (MPE) limits
  • Correct Answer
    Ensure signals from your station are less than the uncontrolled Maximum Permitted Exposure (MPE) limits
  • Ensure signals from your station are less than the controlled Maximum Permitted Emission (MPE) limits
  • Ensure signals from your station are less than the uncontrolled Maximum Permitted 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 to 3 MHz
  • 3 to 30 MHz
  • Correct Answer
    30 to 300 MHz
  • 300 to 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?
  • Only the most powerful transmitter
  • Only commercial transmitters
  • 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 is one of the potential hazards of operating in the amateur radio microwave bands?
  • Microwaves are ionizing radiation
  • Correct Answer
    The high gain antennas commonly used can result in high exposure levels
  • Microwaves often travel long distances by ionospheric reflection
  • 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) field MPE limits?
  • The body reacts to electromagnetic radiation from both the E and H fields
  • Ground reflections and scattering make the field strength 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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How may dangerous levels of carbon monoxide from an emergency generator be detected?
  • By the odor
  • Correct Answer
    Only with a carbon monoxide detector
  • Any ordinary smoke detector can be used
  • By the yellowish appearance of the gas

Carbon monoxide is a colorless, odorless, and tasteless gas. It's a little lighter than air and will rise filling a space from the top down. The only way to detect the gas is with a carbon monoxide detector. The gas is also called carbonous oxide and has one atom of carbon and one atom of oxygen.

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What does SAR measure?
  • Synthetic Aperture Ratio of the human body
  • 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 insulating material commonly used as a thermal conductor for some types of electronic devices is extremely toxic if broken or crushed and the particles are accidentally inhaled?
  • Mica
  • Zinc oxide
  • Correct Answer
    Beryllium Oxide
  • Uranium Hexafluoride

Beryllium Oxide (BeO) is listed as a serious respiratory irritant and probable carcinogenic. Why is it used? Because while most electrical insulators are poor thermal conductors, BeO is good at both. Because it is both a good electrical insulator and a good thermal conductor, it is used in semiconductors and in some vacuum tubes. If either of these types of devices are damaged, be aware of any white dust, as it may be BeO, which is a white ceramic material. Avoid skin contact or inhalation. You can also determine if BeO is used by consulting the manufacturers data sheet. Further information is available on the MSDS (Material Safety Data Sheet) for BeO, several of which may be found using an internet search.

Test Hint: BO can be very toxic

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What toxic material may be present in some electronic components such as high voltage capacitors and transformers?
  • Correct Answer
    Polychlorinated biphenyls
  • Polyethylene
  • Polytetrafluoroethylene
  • Polymorphic silicon

You may recognize these as PCB's because they were commonly used and attracted a considerable amount of bad press. PCB's had the advantage of improving the stability and insulating qualities of transformer oil. Unfortunately, they were also shown to be carcinogenic and were subsequently removed from future use. This is mostly a problem in older, large transformers and capacitors.

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Which of the following injuries can result from using high-power UHF or microwave transmitters?
  • Hearing loss caused by high voltage corona discharge
  • Blood clotting from the intense magnetic field
  • Correct Answer
    Localized heating of the body from RF exposure in excess of the MPE limits
  • Ingestion of ozone gas from the cooling system

Basically a high power UHF or microwave transmitter is doing the same thing as what a microwave oven would do; the frequency may be different, but higher UHF and microwave RF radiation can cause localized heating, just like a microwave would if you ran it with the door open and stuck your arm in.

The specific area that would be heated and the severity of the damage would depend on the frequency and the radiation pattern of the antenna, but you should always be cautious whenever using a high power UHF or microwave signal.

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