No matter what amateur radio activities you engage in, I hope that you will engage in them safely. Every year, we lose amateur radio operators because of injuries they sustained while putting up antennas or doing things that could be dangerous.
Perhaps the most common danger is from RF exposure. The dangers from RF exposure differ from those posed by exposure to radioactive materials. What, if any, are the differences between the radiation produced by radioactive materials and the electromagnetic energy radiated by an antenna? Radioactive materials emit ionizing radiation, while RF signals have less energy and can only cause heating. (E0A01)
The amount of heating is proportional to the specific absorption rate (SAR). SAR measures the rate at which RF energy is absorbed by the body. (E0A08) OIn general, the SAR increases as the frequency increases. Localized heating of the body from RF exposure in excess of the MPE limits is an injury that can result from using high-power UHF or microwave transmitters. (E0A11) One of the potential hazards of using microwaves in the amateur radio bands is that the high gain antennas commonly used can result in high exposure levels. (E0A05)
The FCC, as you might expect, has a lot to say about RF exposure. They have set limits on the field strengths that humans may be exposed to. These limits are called maximum permissible exposure, or MPE.
The MPEs for the electric field and magnetic field of an electromagnetic wave differ. All of these choices are correct as to why there are separate electric (E) and magnetic (H) field MPE limits (E0A06):
- The body reacts to electromagnetic radiation from both the E and H fields
- Ground reflections and scattering make the field impedance vary with location
- E field and H field radiation intensity peaks can occur at different locations
One way to make sure that the field strengths that your transmissions expose you and others to is to measure the absolute field strengths. Unfortunately, this is not easy to do. The equipment used to measure field strength is very expensive and difficult to use. An alternative is to use software that calculates field strength. Using an antenna modeling program to calculate field strength at accessible locations would be a practical way to estimate whether the RF fields produced by an amateur radio station are within permissible MPE limits. (E0A03)
Remember to include your neighbors when evaluating RF exposure levels. In some cases, your antennas may actually be closer to your neighbors’ houses than they are to your house. When evaluating RF exposure levels from your station at a neighbor’s home, you must make sure signals from your station are less than the uncontrolled MPE limits. (E0A02)
Typically, amateur repeater stations are located in places where there are transmitters for other radio services, such as cell phone and pager services. These sites should be regularly evaluated so that RF field strengths don’t exceed the MPE limits. When evaluating a site with multiple transmitters operating at the same time, the operators and licensees of each transmitter that produces 5% or more of its MPE exposure limit at accessible locations are responsible for mitigating over-exposure situations. (E0A04)
RF exposure is not the only danger posed by an amateur radio station. For example, in emergency situations, you may want to use a gasoline-powered generator. One of the dangers posed by a gas-powered generator is that its exhaust contains carbon monoxide. Dangerous levels of carbon monoxide from an emergency generator can be detected only with a carbon monoxide detector. (E0A07)
Some of the materials used in electronics pose a danger to amateur radio operators. They are used because they have some desirable electrical property, but may be dangerous if used improperly. For example, beryllium oxide is an insulating material commonly used as a thermal conductor for some types of electronic devices that is extremely toxic if broken or crushed and the particles are accidentally inhaled. (E0A09) Polychlorinated biphenyls, or PCBs, is a material found in some electronic components, such as high-voltage capacitors and transformers, that is considered toxic. (E0A10)
Leave a Reply