Lesson 35

RF hazards, radiation exposure, RF heating hazards,
proximity to antennas, recognized safe power levels, hand held
safety, exposure to others

In recent years there has been a growing concern in regards to RF fields and health. This has lead to a great deal of research with few positive conclusions. Physiological functions changes have been observed when the human body is in the presence of RF energy fields even when the levels are too low to cause heating. These functional changes return to normal when the radiation field is removed.

Because of the concern the FCC has established limits on the exposure levels of radio frequency transmission which a person should be subjected to. Some information about these RF field exposure limitations is included in the Technician class exam.

Radiation fields such as x-ray, gamma ray, and ultraviolet radiation are classified as “ionizing radiation” while the much lower frequencies of VHF and UHF radiation are classified as “nonionizing radiation.”

Radio waves can cause injury to the human body only if the combination of signal strength and frequency cause excessive power to be absorbed by the body’s tissue thus the maximum power levels which may be used by an amateur radio station above 30 MHz before an RF exposure evaluation is required is 50 Watts PEP at the antenna.

The RF frequency and power level along with the radiation pattern and the distance a person is from the antenna all are factors in regards to the level of exposure a person has to a Radio transmission. The reason frequency must be considered is because the human body will absorb more RF energy at some frequencies then at others.

To determine if an amateur radio station is in compliance with the prescribed RF exposure levels set by the FCC a calibrated field strength meter can be used. Calculations based on FCC OET Bulletin 65 and calculations based on computer modeling can are two other options. The field strength is measured in milliwatts per square centimeter. The amount of time the transmitter is operating, known as “Duty Cycle” is used to make these calibrations.

Care should be taken to be sure no one is able to come in contact with a transmitter antenna while it is in use. Accidental contact with an antenna while the transmitter is operating can result in a very sever and very painful RF burn.

An amateur radio operator might alter the antenna pattern, relocate the antenna, or change the stations parameters such as frequency or power in order to prevent exposure to excessive RF radiations and stay within the FCC limits.

An amateur station should be re-evaluated whenever an item of equipment is changed to be sure the station remains in compliance with the FCC RF safety regulations.



1. T0C01 (D)
What type of radiation are VHF and UHF radio signals?
A. Gamma radiation
B. Ionizing radiation
C. Alpha radiation
D. Non-ionizing radiation
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2. T0C02 (B)
When can radio waves cause injury to the human body?
A. Only when the frequency is below 30 MHz
B. Only if the combination of signal strength and frequency cause excessive power to be absorbed
C. Only when the frequency is greater than 30 MHz
D. Only when transmitter power exceeds 50 watts
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3. T0C03 (C) [97.13(C)(1)]
What is the maximum power level that an amateur radio station may use at frequencies above 30 MHz before an RF exposure evaluation is required?
A. 1500 watts PEP transmitter output
B. 1 watt forward power
C. 50 watts PEP at the antenna
D. 50 watts PEP reflected power
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4. T0C04 (D)
What factors affect the RF exposure of people near an amateur transmitter?
A. Frequency and power level of the RF field
B. Distance from the antenna to a person
C. Radiation pattern of the antenna
D. All of these answers are correct
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5. T0C05 (D)
Why must the frequency of an RF source be considered when
evaluating RF radiation exposure?
A. Lower frequency RF fields have more energy than higher
frequency fields
B. Lower frequency RF fields do not penetrate the human body
C. Higher frequency RF fields are transient in nature and do not
affect the human body
D. The human body absorbs more RF energy at some frequencies than others
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6. T0C06 (D) [97.13(c)(1)]
How can you determine that your station complies with FCC RF exposure regulations?
A. By calculation based on FCC OET Bulletin 65
B. By calculation based on computer modeling
C. By measurement of field strength using calibrated equipment
D. All of these choices are correct
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7. T0C07 (B)
What could happen if a person accidentally touched your antenna while you were transmitting?
A. Touching the antenna could cause television interference
B. They might receive a painful RF burn injury
C. They would be able to hear what you are saying
D. Nothing
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8. T0C08 (D)
What action might amateur operators take to prevent exposure to RF radiation in excess of FCC supplied limits?
A. Alter antenna patterns
B. Relocate antennas
C. Change station parameters such as frequency or power
D. All of these answers are correct
~~
8. T0C09 (B)
How can you make sure your station stays in compliance with RF safety regulations?
A. Compliance is not necessary
B. By re-evaluating the station whenever an item of equipment is changed
C. By making sure your antennas have a low SWR
D. By installing a low pass filter
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10. T0C10 (A)
Which of the following units of measurement is used to measure RF radiation exposure?
A. Milliwatts per square centimeter
B. Megohms per square meter
C. Microfarads per foot
D. Megahertz per second
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11. T0C11 (A)
Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?
A. It takes into account the amount of time the transmitter is operating
B. It takes into account the transmitter power supply rating
C. It takes into account the antenna feed line loss
D. It takes into account the thermal effects of the final
amplifier
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DBCDDDBDBAA