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.)

Last edited by jsharris1229. Register to edit

Tags: radio waves uhf vhf safety

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.

Last edited by drfuka. Register to edit

Tags: 6 meter

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.

Last edited by fuzzyeuk. Register to edit

Tags: safety vhf antenna transmit power

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.

Last edited by ham_noob. Register to edit

Tags: safety radio waves transmit power frequencies antenna

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.

Last edited by kd7bbc. Register to edit

Tags: safety radio waves

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.

Last edited by bud 357. Register to edit

Tags: safety radio waves

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.

Last edited by benton. Register to edit

Tags: antenna safety

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.

Last edited by cstromc. Register to edit

Tags: safety fcc operating procedures antenna

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.

Last edited by archigan. Register to edit

Tags: safety radio operation

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.

Last edited by kabob. Register to edit

Tags: safety radio operation

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.

Last edited by vulcan. Register to edit

Tags: radio operation