Why radio waves heat rather than ionize, what sets your exposure, and who has to make sure your station complies.
Syllabus: RF hazards: radiation exposure, proximity to antennas, recognized safe power levels, radiation types, duty cycle
Compendium articles on the ideas in this lesson, beyond what the exam asks.
Practise the 13 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".
RF has too little energy to cause chemical changes in cells. Its hazard is heating. Touching an antenna while transmitting gives an RF burn to the skin.
All four matter: frequency, power, distance, and the antenna's radiation pattern. To cut exposure, relocate the antenna farther from people.
The limit varies with frequency because the body absorbs more RF at some frequencies than others. Of 3.5, 50, 440 and 1296 MHz, 50 MHz has the lowest limit.
RememberMore power or closer in the beam, more exposure. Limits are tightest around VHF.
Duty cycle is the percentage of time a transmitter is transmitting. Limits use the average exposure, so transmitting less lets you run more.
Drop from 100% to 50% and the allowed power density doubles.
RememberDuty cycle = % of time on air. Half the time, double the allowance.
You may check by calculation (OET Bulletin 65), computer modeling or measurement with calibrated equipment. Re-evaluate whenever anything in the transmitter or antenna system changes. SWR and approved-equipment labels aren't the test.
RememberResponsibility: you, the licensee. Re-evaluate after every change.