Electromagnetic energy may be considered as ionizing and non-ionizing radiation. When radiation is 'ionizing,' it means that it can separate electrons from an atom to create ions. Lower frequency radiation, which includes all amateur radio frequencies, is non-ionizing. Regardless of the power of the signal, the frequecies of VHF and UHF signals are too low to dislodge the electrons. (Gamma and alpha radiation are both ionizing radiation.)

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Tags: radio waves uhf vhf safety arrl chapter 9 arrl module 23

Experimental data indicates the frequencies that are easiest for the human body to absorb are between 30 MHz and 300 MHz. This means that this range requires the lowest exposure or MPE. Since only 50 MHz falls in this range, it is the correct answer. All other frequencies are not within MPE limits.

Tricky question since easy absorption gives 30 - 300 MHz the HIGHEST value, or risk, of reaching a maximum exposure limit.

Additional information and a great chart can be found here.

Maximum Permissible Exposure (MPE) to radiofrequency electromagnetic fields.

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Tags: 6 meter arrl chapter 9 arrl module 23

The FCC considers power levels less than 50 watts PEP as not being a significant risk to people and has issued rules excluding stations operating in the range from performing an evaluation. Obviously, this includes the smaller hand-held radios. Therefore, when a station reaches or exceeds 50 watts PEP at the antenna, an RF exposure evaluation is required.

Reflected power depends on what it's being reflected by, so that choice can be discarded.

Not many radios use less than 1 watt, so that can be discarded too.

RF exposure is measured at the antenna, not at the transmitter output.

Comparing the answers to typical small microwave oven power, 700 watts, gives an idea for when a power level could start to be a concern. 1500 watts is twice the power level of a small microwave oven, so an evaluation would be required far before this power level is reached.

For More information on PEP (peak envelope power) go to http://www.radio-electronics.com/info/t_and_m/rf-microwave-power-meter/peak-envelope-average-pulse-power.php

tl;dr, its the maximum power or spike during a cycle.

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Each of these answers affect a persons exposure to RF energy radiating from an antenna. The frequency of the signal determines how easily the body absorbs the RF energy. As the power level of the signal increases, more energy can be absorbed, increasing the exposure. The distance is important because the power level of the signal drops rapidly with distance. Finally, the radiation pattern indicates the areas where the energy is directed and how it is concentrated.

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The body absorbs energy differently at different frequencies because different materials and parts of your body are resonant at different frequencies.

The other answers listed can also be seen to be incorrect: RF field energy does not depend on frequency, lower RF frequencies can penetrate the body, and higher frequency RF fields are not transient in nature any more than any other frequency.

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Tags: safety radio waves arrl chapter 9 arrl module 23

All of these are correct. In most cases, either the FCC OET Bulletin 65 (found at http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf) or computer modeling are sufficient.

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The human body absorbs RF energy and acts like a resistor. A resistor turns electrical energy into heat energy. If the body absorbs too much RF energy, it means that it will create enough heat to damage tissue in the form of a burn, a painful RF burn. Touching an antenna will not cause radiation poisoning because RF is non-ionizing radiation and thus lacks the energy required to cause it.

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RF radiation "radiates" outward from the antenna, therefore, it is the antenna that must be moved. Relocating the transmitter will have no effect, provided the transmitter is connected to the antenna correctly. Increasing the duty cycle would have the reverse effect - it would increase your exposure.

Duty cycle is the ratio of how much time the transceiver spends transmitting to how much it spends receiving; thus, the more you transmit, the higher your duty cycle.

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Any time you change your equipment, it's a good idea to re-evaluate your station to ensure compliance. You do not inform the FCC because the amateur service is designed to be self-policing. The SWR of your system will only ensure efficient power transfer, not compliance with safety regulations.

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Duty cycle affects average exposure level, which is what the Maximum Permissible Exposure (MPE) limits are based on. A person is more likely to tolerate a one- time, high peak exposure of very short duration than a lower exposure over a long period of time. This is where duty cycle is important because it is a measure of the transmit and non-transmit times, which determines the average exposure. Antenna feedline losses and amplifier thermal effects have nothing to do with RF exposure.

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The duty cycle is made up of 'on' times and 'off' times. It is defined as the ratio of on-air time to total operating time. A 40% duty cycle means that 40% of the time, the station will be transmitting.

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RF energy cannot break chemical bonds, they don't have the energy required to cause genetic damage.

Source: According to John E. Moulder (Biological Effects of Power-frequency Fields as they Relate to Carcinogenesis, University of Wisconsin, 1995, p. 209:309-324), professor of Radiation Oncology, because non-ionizing electromagnetic (RF) energy cannot break chemical bonds, they don't have the energy required to cause genetic damage.

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Tags: arrl chapter 9 arrl module 23

Exposure to radiation is measured by the amount of energy (E) absorbed from that radiation. Power density (P_D) is the amount of energy absorbed per unit of time from a given distance squared, so

P_D = E / time / r², or E = P_D X time X r²

For a six-minute average exposure,

E₆ = P_D6 X 6 minutes X r²= 6P_D6r²

But if the same signal was applied for three minutes on and then three minutes off from the same distance,

E₃ = P_D3 X 3 minutes X r² + 0 X 3 minutes X r²= 3P_D3r².

If the same exposure (maximum permitted) is experienced in both cases,

E₆ = E₃, or substituting,

6P_D6r² = 3P_D3r², so that

P_D3 = 2P_D6

Therefore, twice as much power density would be permitted for the three-minute-on-then-off case as with the six-minute-full-on case, so the answer is 2 times as much.

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