T0 Safety

B. Shorting the terminals can cause burns, fire, or an explosion

A 12-volt storage battery can deliver a large current, and a short circuit across its terminals, for example from a dropped wrench or a loose wire, can heat metal enough to cause burns, start a fire, or make the battery explode. Without protection circuitry, nothing limits that current.

• A. 12 volts is too low to push a dangerous current through dry skin, so touching both terminals does not normally cause a shock; the danger is the high current available through a short.
• C. RF from a nearby transmitter does not make battery electrolyte give off poison gas.
• D. Shock from touching the terminals and RF-caused poison gas are not real hazards of a 12-volt battery, so not all the choices are correct.

D. All these choices are correct

Current flowing through the body harms it in several ways: it heats tissue and causes burns, it disrupts the electrical signals that nerve and heart cells depend on, and it causes involuntary muscle contractions that can keep a person from letting go of a live conductor.

• A. True: current heats body tissue and can cause internal and external burns, but this is only one of the hazards.
• B. True: current can disrupt the electrical functions of cells, including the heart's rhythm, but this is only one of the hazards.
• C. True: current can make muscles contract involuntarily, which can prevent a person from releasing a live conductor, but this is only one of the hazards.

B. Hot

In US AC wiring, black insulation marks the hot conductor, which carries the line voltage. White is the neutral, and green or bare copper is the equipment ground.

• A. The neutral conductor is white, not black.
• C. The equipment ground is green or bare copper, not black.
• D. Negative is a DC term; a three-wire 120 V AC cable has hot, neutral and ground conductors.

B. To remove power in case of an overload

A fuse is a deliberate weak link: its metal element melts and opens the circuit when current exceeds its rating, removing power during an overload or short circuit. This protects wiring and equipment from overheating and fire.

• A. Ripple is a small AC variation on a DC supply's output; a fuse does nothing to reduce it.
• C. A fuse does not limit current or prevent shocks; it opens only after current exceeds its rating, and a current that can cause a dangerous shock is far below typical fuse ratings.
• D. A fuse only removes power on overload; it does not reduce ripple or prevent shocks, so not all the choices are correct.

C. Excessive current could cause a fire

A fuse must match the current that the circuit's wiring and parts can safely carry. A 20-ampere fuse in place of a 5-ampere fuse lets four times as much current flow before it opens (20 A / 5 A = 4), so a fault can overheat wires and components and start a fire.

• A. A higher-rated fuse is less likely to blow, not more; that is why it is dangerous.
• B. The fuse rating has no effect on power supply ripple.
• D. Voltage drop across a fuse is small for either rating; the danger of the larger fuse is that it does not open during a fault.

D. All these choices are correct

Several practices guard against shock: three-wire cords and plugs connect equipment cases to the safety ground, a common safety ground keeps all station equipment at the same potential, and discharging high-voltage capacitors removes stored energy before you work inside equipment.

• A. True: the third wire grounds the equipment case so that a fault trips the breaker instead of making the case live, but this is only one of the precautions.
• B. True: a common safety ground prevents dangerous voltage differences between pieces of equipment, but this is only one of the precautions.
• C. True: high-voltage capacitors can hold a dangerous charge after power is removed, but discharging them is only one of the precautions.

D. On a grounded panel near where feed lines enter the building

A lightning arrester for a coaxial feed line belongs on a grounded panel near where the feed lines enter the building, bonded to the station's grounding system. There it diverts surge current to ground before the surge can enter the building and reach equipment.

• A. At the transceiver, the surge has already entered the building and can damage equipment and wiring along the way.
• B. At the antenna feed point, the arrester is far from the building's ground, and the feed line into the house is left unprotected.
• C. The AC service panel handles the power wiring, not the coaxial feed line; the feed line arrester goes where the coax enters the building.

A. In series with the hot conductor only

A fuse or circuit breaker goes in series with the hot conductor, so all current to the load passes through it and opening it disconnects the line voltage. The neutral is not fused, because opening only the neutral would leave the equipment connected to the hot line and still energized.

• B. Fusing the neutral is unsafe: if the neutral fuse opens first, the equipment is still connected to the hot conductor.
• C. A fuse in parallel with the hot conductor shares current with the wire, so opening it would not disconnect the load.
• D. A fuse in parallel across the hot and neutral conductors would short the supply rather than protect the circuit.

C. Bond them together with heavy wire or conductive strap

All ground rods and earth connections at a station should be bonded together with heavy wire or conductive strap so they stay at the same potential. During a lightning strike or power fault, unbonded grounds can have large voltage differences between them, driving dangerous currents through equipment and cables connected between them.

• A. Waterproofing does not address the hazard; separate grounds must be bonded together so they stay at the same potential.
• B. Spreading ground rods apart without bonding them allows large voltage differences between them during a strike or fault.
• D. Ground rods are not tuned; they provide a path to earth for safety and lightning protection, not a resonant antenna element.

A. Overheating or out-gassing

Charging or discharging a battery rapidly forces a large current through it, which heats it and can cause out-gassing, the release of gas from the cells. An unprotected battery has no circuitry to limit this, and the result can be fire, rupture, or explosion.

• B. Ripple is a property of power supplies that rectify AC, not a hazard of rapidly charging or discharging a battery.
• C. Typical storage batteries are low voltage; the hazard of rapid charging or discharging is heat and gas, not shock.
• D. Overvoltage is not the hazard described; rapid charging or discharging causes overheating and out-gassing.

D. Charge stored in filter capacitors

Filter capacitors in a power supply can hold their charge after the power is turned off, keeping a dangerous voltage on the circuit. Bleeder resistors are often used to discharge them, but verify that the capacitors are discharged before touching anything inside.

• A. Current in the filter stops shortly after power is removed; the stored charge in the capacitors is the remaining hazard.
• B. Leakage flux exists only while the transformer is energized; it disappears when the power is off.
• C. Kickback diodes suppress voltage spikes from inductive loads such as relay coils; they do not store energy after turn-off.

B. Ensure that the voltmeter and its leads are rated for use at the voltages being measured

When measuring high voltage, both the voltmeter and its test leads must be rated for the voltage being measured. A meter or leads with too low a rating can arc over or break down and expose you to the high voltage.

• A. A voltmeter should have high impedance, not low; a low-impedance meter draws current from the circuit and disturbs the measurement.
• C. The meter should never be a path to ground for the circuit; that creates a shock and damage hazard.
• D. Voltmeters are not set to a frequency; you select AC or DC and a suitable voltage range.

C. Ensure that connections are short and direct

Lightning current rises very fast, so any extra length or sharp bend in a ground wire adds impedance and a large voltage. Keeping ground connections short and direct gives the current a low-impedance path to earth.

• A. A drip loop belongs on feed lines entering a building to shed water; in a ground wire, a loop adds length and impedance.
• B. Sharp right-angle bends raise the impedance to lightning current and invite arcing; bends in ground wires should be gradual.
• D. Drip loops and right-angle bends are poor practice for lightning ground wires, so not all the choices are correct.

D. All these choices are correct

Safe tower climbing requires training in safe climbing techniques, an approved climbing harness, and staying tied off to the tower at all times so that a slip does not become a fall.

• A. True: training teaches safe climbing and work methods, but it is only one of the requirements.
• B. True: staying tied off at all times prevents falls, but it is only one of the requirements.
• C. True: an approved harness is the attachment point for fall protection, but it is only one of the requirements.

D. Never

Never climb a tower without a helper or observer on the ground. A helper can pass up tools, keep people clear of the area below, and call for emergency help if the climber is injured or stranded.

• A. Falls and injuries can happen whether or not electrical work is being done.
• B. Falls and injuries can happen whether or not mechanical work is being done.
• C. A fall from 20 feet can cause serious injury or death, so no height is safe to work alone.

C. Look for and stay clear of any overhead electrical wires

Contact with overhead power lines while raising a tower or antenna can kill. Before starting, locate all overhead wires and plan the work so that no part of the tower, antenna, or rigging can come near them.

• A. A wrist ground strap protects electronic parts from static discharge at a workbench; it offers no protection during tower work.
• B. Towers should be grounded, not insulated, so lightning current has a direct path to earth.
• D. A wrist strap and an insulated tower base are not safety measures for tower work, so not all the choices are correct.

B. Prevent loosening of the turnbuckle from vibration

Turnbuckles tension guy lines, and vibration from wind can slowly turn them and loosen the guys. A safety wire passed through the turnbuckle keeps it from turning.

• A. The safety wire is there to keep the turnbuckle from turning, not to hold the guy line's load.
• C. Lightning protection comes from grounding the tower and guys, not from a turnbuckle safety wire.
• D. A safety wire does not measure tension; its purpose is to keep the turnbuckle from loosening.

D. Enough so that if the antenna falls, no part of it can come within 10 feet of the power wires

Place an antenna far enough from power lines that, if it falls in any direction, no part of it can come within 10 feet of the wires. Antennas and their supports can fall during installation or in storms, and contact with power lines can be fatal.

• A. This formula is not the safety guideline; the guideline is that a falling antenna must stay at least 10 feet from the wires.
• B. The height of the power line alone ignores the size of the antenna and its support, which determine where it can land if it falls.
• C. Wavelength has nothing to do with physical clearance; what matters is where the antenna could land if it falls, plus 10 feet.

C. This type of tower must not be climbed unless it is retracted, or mechanical safety locking devices have been installed

A crank-up tower's sections are raised and held by cables and a winch. Climbing it while extended puts your weight on that mechanism and risks a sudden collapse, so it must not be climbed unless it is fully retracted or mechanical safety locking devices are installed.

• A. Paint has nothing to do with crank-up tower safety; the hazard is climbing it while it is extended.
• B. Crank-up towers, like all towers, should be grounded for lightning protection.
• D. Painting is not prohibited and grounding is required, so not all the choices are correct.

D. Separate eight-foot ground rods for each tower leg, bonded to the tower and each other

A tower should be grounded with a separate 8-foot ground rod at each leg, with the rods bonded to the tower and to each other. Several long rods give lightning current multiple low-impedance paths into the earth, and bonding keeps them at the same potential.

• A. A single short rod makes too little contact with the earth for lightning current; a rod at each leg, bonded together, is the practice to follow.
• B. An RF choke would add impedance to the ground path, the opposite of what lightning protection needs.
• C. A cold-water pipe is not a dependable ground, since pipes may be plastic, and it would route lightning current into the building's plumbing.

C. The antenna could contact high-voltage power lines

Utility poles carry high-voltage power lines, and an antenna mounted on one could touch those lines during installation, in wind, or if it breaks. Contact can be fatal for anyone touching the antenna, its feed line, or connected equipment.

• A. Induced voltage affecting antenna performance is not the reason; the danger is contact with high-voltage lines.
• B. An antenna does not unbalance a power transformer; the danger is physical contact with the lines.
• D. Only the risk of contact with high-voltage lines is the reason, so not all the choices are correct.

C. Sharp bends must be avoided

Lightning current rises very quickly, and a sharp bend in a grounding conductor raises its impedance and can make the current arc across to nearby objects. Grounding conductors should run as short and straight as possible, with gradual bends where needed.

• A. Grounding conductors may be insulated or bare; what matters is a short, direct path without sharp bends.
• B. Right-angle bends are what to avoid; sharp bends raise impedance and can cause arcing.
• D. Common grounds are desirable: all grounds should be bonded together so they stay at the same potential.

B. Local electrical codes

Grounding requirements for towers and antennas are set by local electrical codes, which are usually based on the National Electrical Code (NEC) as adopted by the state or local government. Part 97 does not set grounding requirements.

• A. Part 97 governs radio operation and does not set grounding requirements for towers or antennas.
• C. FAA rules concern marking and lighting of tall structures near airports, not grounding.
• D. UL (Underwriters Laboratories) tests and certifies products; it does not set legal grounding requirements for towers.

D. Non-ionizing radiation

Radio waves are non-ionizing radiation: each photon carries far too little energy to knock electrons out of atoms or break chemical bonds. The main biological effect of strong RF fields is heating of body tissue.

• A. Gamma rays are very high-energy electromagnetic radiation from nuclear processes, and they are ionizing; radio waves are not.
• B. Ionizing radiation, such as X-rays and gamma rays, has enough energy per photon to remove electrons from atoms; radio waves do not.
• C. Alpha radiation is a stream of particles (helium nuclei) from radioactive materials, not electromagnetic waves.

B. 50 MHz

The FCC maximum permissible exposure (MPE) limits in 47 CFR 1.1310 are lowest from 30 to 300 MHz, where the human body absorbs RF energy more efficiently than at other frequencies. The general population limit there is 0.2 mW/cm², and 50 MHz falls in that range.

• A. At 3.5 MHz the general population limit is 180/f² = 180 / 3.5² ≈ 14.7 mW/cm², far higher than at 50 MHz.
• C. At 440 MHz the general population limit is f/1500 = 440 / 1500 ≈ 0.29 mW/cm², higher than the 0.2 mW/cm² limit at 50 MHz.
• D. At 1296 MHz the general population limit is f/1500 = 1296 / 1500 ≈ 0.86 mW/cm², higher than the 0.2 mW/cm² limit at 50 MHz.

C. It increases by a factor of 2

FCC exposure limits are averaged over time (up to 30 minutes for the general population and 6 minutes for occupational exposure, under 47 CFR 1.1310). With a 50 percent duty cycle the average exposure is half that of continuous transmission, so the power density while transmitting can be twice as high (100 / 50 = 2) and still meet the same average limit.

• A. A factor of 3 would correspond to a duty cycle of about 33 percent (100 / 33.3 ≈ 3), not 50 percent.
• B. A lower duty cycle lowers average exposure, so the allowable power density goes up, not down.
• D. The limits are time-averaged (47 CFR 1.1310(d)(4)), so a lower duty cycle does allow a higher power density.

D. All these choices are correct

RF exposure depends on the field strength where people are. That depends on the transmitter's frequency and power, the distance from the antenna (fields weaken quickly with distance), and the antenna's radiation pattern, which concentrates energy in some directions.

• A. True: power sets the field strength and frequency sets the exposure limit, but these are only part of the answer.
• B. True: exposure falls off quickly with distance from the antenna, but distance is only one of the factors.
• C. True: the radiation pattern decides where the strongest fields go, but it is only one of the factors.

D. The human body absorbs more RF energy at some frequencies than at others

The human body absorbs RF energy more efficiently at some frequencies than at others. Whole-body absorption peaks roughly in the 30 to 300 MHz range, where the body's size is comparable to a resonant length, so the FCC limits in 47 CFR 1.1310 are lowest in that range and higher where absorption is lower.

• A. Lower frequency RF does not carry more energy; photon energy rises with frequency, and RF at any frequency is non-ionizing.
• B. Lower frequency RF does penetrate the body, generally more deeply than higher frequencies; the limits vary because of how much energy is absorbed.
• C. RF fields at higher frequencies are not transient; the limits vary because absorption by the body varies with frequency.

D. All these choices are correct

The FCC accepts several ways to evaluate a station's RF exposure: calculations using the methods in FCC OET Bulletin 65, calculations from computer modeling of the antenna, or measurements of field strength with calibrated equipment. 47 CFR 97.13(c)(1) points amateurs to OET Bulletin 65, Supplement B for evaluation methods.

• A. True: OET Bulletin 65 gives formulas and tables for estimating exposure, but it is only one acceptable method.
• B. True: computer modeling can estimate field strengths around an antenna, but it is only one acceptable method.
• C. True: calibrated field strength measurements show actual exposure levels, but they are only one acceptable method.

B. RF burn to skin

A transmitting antenna carries RF voltage and current, and touching it can cause an RF burn where the current passes into the skin. RF burns can be painful and deep even at modest power levels.

• A. Electrocution means a fatal electric shock, typically from power-line or high-voltage DC sources; the usual hazard from touching a transmitting antenna is an RF burn.
• C. RF energy is non-ionizing, so touching an antenna does not expose you to ionizing radiation.
• D. Electrocution and ionizing radiation are not the hazards of touching a transmitting antenna, so not all the choices are correct.

A. Relocate antennas

RF exposure decreases with distance from the antenna, so moving antennas farther from where people are, such as higher up or away from living areas, reduces exposure. The antenna is what radiates, so it is the part whose location matters.

• B. A properly shielded transmitter radiates little; exposure comes mainly from the antenna, so moving the transmitter does not help.
• C. Increasing the duty cycle raises average exposure, the opposite of what is wanted.
• D. Moving the transmitter and increasing duty cycle do not reduce exposure, so not all the choices are correct.

B. By re-evaluating the station whenever an item in the transmitter or antenna system is changed

An RF exposure evaluation applies to a particular combination of transmitter, power, frequency, feed line and antenna. Re-evaluate the station whenever any item in the transmitter or antenna system changes, to confirm that it still complies.

• A. Amateurs do not report station changes to the FCC; the licensee is responsible for keeping the station in compliance.
• C. Low SWR shows a good match between feed line and antenna, but a well-matched antenna can still produce excessive exposure.
• D. UL listing concerns electrical product safety, not the RF exposure produced by your antenna installation.

A. It affects the average exposure to radiation

FCC exposure limits are time-averaged, so what matters is the average exposure over the averaging period. Duty cycle, the fraction of time the transmitter is on, scales that average: a transmitter on half the time produces half the average exposure of one transmitting continuously.

• B. Duty cycle does not change the peak exposure; while transmitting, the field is as strong as at any other time.
• C. Feed line loss reduces the power reaching the antenna, but it is a separate factor from duty cycle.
• D. Heating of the final amplifier concerns the transmitter, not human RF exposure.

C. The percentage of time that a transmitter is transmitting

Duty cycle is the percentage of time that a transmitter is transmitting during the averaging period. For example, transmitting for 3 minutes out of every 6 is a 50 percent duty cycle (3 / 6 = 0.5).

• A. The difference between lowest and highest power output is a range of power, not a measure of time.
• B. The relationship between PEP and average power depends on the modulation, not on how long the transmitter is on.
• D. This is the opposite: duty cycle measures time transmitting, not time not transmitting.

A. RF radiation does not have sufficient energy to cause chemical changes in cells and damage DNA

Ionizing radiation, such as X-rays and gamma rays, carries enough energy per photon to cause chemical changes in cells and damage DNA. RF photons have far too little energy to do this; the main effect of strong RF fields is heating of tissue.

• B. RF can be detected and measured with ordinary instruments such as field strength meters, not only with dosimeters.
• C. RF signals travel great distances, which is why radio communication works; field strength falls with distance, but RF is not limited to a few feet.
• D. RF is not perfectly safe; strong fields can heat tissue and cause burns, which is why the FCC sets exposure limits.

B. The station licensee

Under 47 CFR 97.13(c), the station licensee must ensure that the station does not expose people to RF fields above the limits in 47 CFR 1.1310, and must take action to prevent such exposure if an evaluation shows the limits could be exceeded in accessible areas.

• A. The FCC sets the exposure limits, but the station licensee is responsible for making sure the station meets them.
• C. People near an antenna are not responsible; the licensee must keep exposure in accessible areas within the limits.
• D. Zoning boards regulate land use, not RF exposure from amateur stations.