RF safety principles, rules and guidelines, routine station evaluation
If you learn nothing else from this manual, I hope that you learn to be safe when setting up your station, building antennas, or operating a radio. It’s unfortunate, but hams every year lose their lives in accidents that could have been prevented. In this chapter, we will cover RF safety and electrical safety.
By RF safety, we mean staying below the limits for exposure to the RF energy generated by amateur radio transmitters. These limits are set by the FCC and are called maximum permissible exposure, or MPE.
To determine the amount of RF that you’ve been exposed to you have to take into account the time you’re exposed to the RF radiation, the level of the RF radiation, and the duty cycle of the radiation. One way that RF energy can affect human body tissue is that it heats body tissue.
QUESTION: What is one way that RF energy can affect human body tissue? (G0A01)
ANSWER: It heats body tissue
QUESTION: What does “time averaging” mean in reference to RF radiation exposure? (G0A04)
ANSWER: The total RF exposure averaged over a certain time
QUESTION: What effect does transmitter duty cycle have when evaluating RF exposure? (G0A07)
ANSWER: A lower transmitter duty cycle permits greater short-term exposure levels
QUESTION: Which of the following properties is important in estimating whether an RF signal exceeds the maximum permissible exposure (MPE)? (G0A02)
ANSWER: All of these choices are correct
• Its duty cycle
• Its frequency
• Its power density
It’s important to keep in mind the MPE limits when installing an antenna, especially an indoor transmitting antenna because the closer you, and other people living with you, are to the antenna, the higher the exposure will be.
QUESTION: What precaution should you take if you install an indoor transmitting antenna? (G0A11)
ANSWER: Make sure that MPE limits are not exceeded in occupied areas
To ensure compliance with RF safety regulations when transmitter power exceeds levels specified in part 97.13, you must routinely perform RF exposure evaluations. You can do this by using the evaluation procedure found in FCC OET Bulletin 65 or by computer modeling of your station setup. In some cases, you may actually want to make field strength measurements with a calibrated instrument to ensure your safety.
QUESTION: Which of the following steps must an amateur operator take to ensure compliance with RF safety regulations when transmitter power exceeds levels specified in FCC Part 97.13? (G0A08)
ANSWER: Perform a routine RF exposure evaluation
QUESTION: How can you determine that your station complies with FCC RF exposure regulations? (G0A03)
ANSWER: All of these choices are correct
• By calculation based on FCC OET Bulletin 65
• By calculation based on computer modeling
• By measurement of field strength using calibrated equipment
QUESTION: What type of instrument can be used to accurately measure an RF field? (G0A09)
ANSWER: A calibrated field strength meter with a calibrated antenna
If an evaluation of your station shows RF energy radiated from your station exceeds permissible limits, then you must take action. This might mean reducing your transmitter power or moving antennas. If you use a directional antenna, you should ensure that it cannot be pointed in a direction that would cause people to receive more than the maximum permissible exposure.
QUESTION: What must you do if an evaluation of your station shows RF energy radiated from your station exceeds permissible limits? (G0A05)
ANSWER: Take action to prevent human exposure to the excessive RF fields
QUESTION: What is one thing that can be done if evaluation shows that a neighbor might receive more than the allowable limit of RF exposure from the main lobe of a directional antenna? (G0A10)
ANSWER: Take precautions to ensure that the antenna cannot be pointed in their direction
In addition to ensuring that you’re not exposed to high-energy RF fields, there are some simple precautions that you should take when installing an antenna. The first thing you should do is to turn off the transmitter and disconnect the feedline. Also, if you are installing a ground-mounted antenna, make sure that no one can touch it while you’re transmitting, as doing so may cause RF burns.
QUESTION: What precaution should you take whenever you adjust or repair an antenna? (G0B14)
ANSWER: Turn off the transmitter and disconnect the feed line
QUESTION: What precaution should be taken when installing a ground-mounted antenna? (G0A06)
ANSWER: It should be installed such that it is protected against unauthorized access
Following safe work practices when installing or working on an antenna tower is paramount. Always make sure that anyone climbing the tower is using the appropriate safety belt or harness and that no power can be supplied to any circuits powering devices on the tower.
QUESTION: Which of these choices should be observed when climbing a tower using a safety belt or harness? (G0B07)
ANSWER: Confirm that the belt is rated for the weight of the climber and that it is within its allowable service life
QUESTION: What should be done by any person preparing to climb a tower that supports electrically powered devices? (G0B08)
ANSWER: Make sure all circuits that supply power to the tower are locked out and tagged
Properly grounding a tower is also an important safety practice. Never solder wires that connect a tower to ground, as they will simply be destroyed by a lightning strike. Instead, makes sure that the legs of the tower are properly grounded by bonding them together and then bonding them to the tower’s ground rods.
QUESTION: Why should soldered joints not be used with the wires that connect the base of a tower to a system of ground rods? (G4C07)
ANSWER: A soldered joint will likely be destroyed by the heat of a lightning strike
QUESTION: Which of the following is good practice for lightning protection grounds? (G0B11)
ANSWER: They must be bonded together with all other grounds
Station safety: electrical shock, safety grounding, fusing, interlocks, wiring, antenna and tower safety
When wiring your station or “shack,” pay special attention to the currents that the circuit must supply and use the appropriate wire sizes and fuse sizes. These values are specified by the National Electrical Code (NEC). You should refer to the NEC for any question you might have about electrical safety.
QUESTION: Which of the following is covered by the National Electrical Code? (G0B06)
ANSWER: Electrical safety inside the ham shack
QUESTION: According the National Electrical Code, what is the minimum wire size that may be used safely for wiring with a 20 ampere circuit breaker? (G0B02)
ANSWER: AWG number 12
QUESTION: Which size of fuse or circuit breaker would be appropriate to use with a circuit that uses AWG number 14 wiring? (G0B03)
ANSWER: 15 amperes
For some devices, such as a linear amplifier, you may have to install a 240 VAC circuit. Again, the National Electrical Code calls out requirements for wiring this kind of circuit. As with 120 VAC circuits, it’s a good idea to use ground fault circuit interrupters (GFCIs) to detect ground faults and prevent unsafe situations from occurring.
QUESTION: Which wire or wires in a four-conductor connection should be attached to fuses or circuit breakers in a device operated from a 240 VAC single phase source? (G0B01)
ANSWER: Only the two wires carrying voltage
QUESTION: Which of the following conditions will cause a Ground Fault Circuit Interrupter (GFCI) to disconnect the 120 or 240 Volt AC line power to a device? (G0B05)
ANSWER: Current flowing from one or more of the voltage-carrying wires directly to ground
Some equipment may have features that make it safer to use or maintain. For example, some power supplies have interlock switches. These switches disconnect the power supply when an enclosure is opened.
QUESTION: What is the purpose of a power supply interlock? (G0B12)
ANSWER: To ensure that dangerous voltages are removed if the cabinet is opened.
In an emergency, you may want to power your station with batteries or an emergency power generator. Again, please do so safely. Always make sure that before turning on a generator, the incoming utility power feed is disconnected, and if you’re using a gasoline-powered generator, operate it in a well-ventilated space away from people.
QUESTION: What must you do when powering your house from an emergency generator? (G0B13)
ANSWER: Disconnect the incoming utility power feed
QUESTION: Which of the following is true of an emergency generator installation? (G0B09)
ANSWER: The generator should be located in a well-ventilated area
QUESTION: Which of the following is a primary reason for not placing a gasoline-fueled generator inside an occupied area? (G0B04)
ANSWER: Danger of carbon monoxide poisoning
Finally, consider that the lead in the solder commonly used in amateur radio equipment might constitute a hazard. Remember what your mother always told you to do before dinner? After using lead-tin solder, wash your hands!
QUESTION: Which of the following is a danger from lead-tin solder? (G0B10)
ANSWER: Lead can contaminate food if hands are not washed carefully after handling
Dave New, N8SBE says
“According the National Electrical Code” –> “According to the National Electrical Code”
Dan KB6NU says
That’s actually an error in the question pool!
Jeannette Walsh says
My experience of how to handle a generator is to Keep the generator dry. Operate your generator on a dry surface under an open, and make sure your hands are dry before touching the generator.