General Class License Study

Part 1 — Operator Knowledge

Safety is the last module in this course, but it is not an afterthought. Every other module in this course teaches you how to communicate. This one teaches you how to stay alive while doing it. Amateur radio involves lethal voltages, RF energy that can cause serious burns, antenna systems that attract lightning, and towers that will kill you if you fall from them. None of these hazards are theoretical. Operators have been killed and seriously injured by every one of them.

Read this module carefully. The habits described here take seconds to form and can prevent injuries that take months to recover from, or that you do not recover from at all. The exam questions in this subelement exist because the FCC wants to verify that every licensed amateur operator understands the basic safety requirements of the service. Learn them to pass the exam. Practice them every time you operate.

Electrical Safety — Current Kills

What Actually Kills You

Most people think voltage kills. Voltage is the cause, but current is what kills you. Voltage determines how much current will flow through your body's resistance. Your body's resistance varies enormously — dry skin on the back of your hand may present 100,000 ohms. Wet skin, abraded skin, or contact across a moist mucous membrane can drop that to 1,000 ohms or less. A surface that seems safe at dry-skin resistance becomes lethal when you are sweating in a hot shack or working outdoors in rain.

At 120V AC with wet skin at 1,000 ohms resistance, Ohm's Law gives you 120 mA — squarely in the "almost certainly fatal" range. Even at 50V, wet skin contact can deliver 50 mA, enough to cause ventricular fibrillation. The voltage thresholds used in safety standards (30V for the one-hand rule, 50V for touch voltage limits) are conservative values based on dry skin. In amateur radio operating conditions — a warm shack, outdoor work, or any situation involving moisture — treat any voltage above 12V as potentially dangerous.

The One-Hand Rule

When you must work on or near energized circuits — at voltages above 30V — keep one hand in your pocket or behind your back. Use only one hand to probe, measure, or adjust. This is not timidity. This is engineering.

The reason: if both hands are in contact with different parts of an energized circuit, current flows from one hand, across your chest, and through your heart to the other hand. This hand-to-hand path runs directly through the heart. Ventricular fibrillation can be triggered by much smaller currents on this path than on other paths through the body.

With one hand behind your back, a contact fault on the hand you are using sends current from your hand, down through your body, and out through whatever you are standing on. This path does not cross the heart. It may produce a painful shock and muscle contractions. It is unlikely to trigger cardiac fibrillation. The one-hand rule has saved lives. Make it an automatic habit.

Capacitor Discharge — Power Off Does Not Mean Safe

Large electrolytic filter capacitors in power supplies store electrical charge. They hold that charge after the power is removed. A fully charged 50,000 μF capacitor bank at 20 volts contains enough energy to weld the tips of a screwdriver in a shower of sparks. At the operating voltages of a tube amplifier's power supply — 2,000 to 5,000 volts — the stored energy in the filter capacitors is sufficient to kill instantly.

The standard protection in power supply design is a bleeder resistor — a resistor connected across the capacitor bank that slowly discharges the capacitors after power is removed. The bleeder resistor value is chosen to discharge the capacitors to a safe voltage within a reasonable time (typically 30 to 60 seconds). However:

• You cannot assume the bleeder resistor has done its job unless you verify it with a voltmeter
• Bleeder resistors fail open, which leaves the capacitors fully charged with no discharge path
• Some equipment does not include bleeder resistors

The correct procedure before working inside any power supply:

1. Remove AC power (unplug or switch off the breaker)
2. Wait at least 60 seconds for bleeder resistors to act
3. With one hand behind your back, measure the voltage across the main filter capacitors with a voltmeter
4. If voltage is not below 30V, discharge the capacitors through a resistive discharge tool (a 25-watt, 10-kilohm resistor on insulated leads)
5. Measure again to confirm discharge before touching any components

This procedure takes less than two minutes. Skipping it has killed operators who were experienced, careful, and knew better. The capacitor that kills you is the one you assumed had discharged.

RF Burns — Do Not Touch a Transmitting Antenna

Radio frequency current passing through tissue heats it. At the power levels used by HF stations, contact with a transmitting antenna or a feedline carrying RF can cause immediate burns. RF burns differ from thermal burns in several important ways:

• They can be deeper than they appear on the surface. The RF energy penetrates tissue and deposits heat below the skin surface where it is not immediately visible
• They are initially less painful than thermal burns of equivalent severity because the nerve endings may also be damaged. Do not underestimate the injury because it does not hurt as much as expected
• They heal more slowly and are more prone to infection than surface thermal burns

Do not touch an antenna, a loading coil, or an exposed feedline while transmitting or immediately after transmitting. Even a brief contact with an antenna carrying 100 watts of RF can produce a significant burn. In field operations, clearly mark any transmitting antenna elements that could be touched accidentally and ensure all personnel in the area are aware of transmit schedules.

RF Safety — MPE Limits and Exposure Evaluation

How RF Energy Affects the Body

RF energy in the range used by amateur radio is non-ionizing radiation — it does not break chemical bonds or damage DNA the way X-rays and gamma radiation do. The biological effect of RF energy is thermal: it heats tissue. The concern is not cancer from brief exposures but thermal injury from sustained exposures above safe limits.

The body tissues most susceptible to RF thermal injury are the eyes and the testes. Both have limited blood flow for cooling compared to other tissues. Sustained RF exposure of the eyes at high power density can cause cataracts. The FCC's MPE limits are designed with these vulnerabilities in mind.

The frequency range of greatest concern for whole-body RF absorption is approximately 30 to 300 MHz, where the human body is most efficient at absorbing RF energy (body resonance). At lower frequencies (HF), the body is less efficient at absorbing RF but contact with transmitting antennas and feedlines is still hazardous as described above. At higher frequencies (microwave), the absorption depth decreases and surface heating becomes the primary concern.

Maximum Permissible Exposure (MPE)

The FCC establishes Maximum Permissible Exposure (MPE) limits for RF fields. These limits define the maximum power density (milliwatts per square centimeter, mW/cm²) that persons may be exposed to continuously without risk of harm. Two categories of exposure limits apply:

Controlled (occupational) exposure: Applies to people who are aware of their RF exposure and can take appropriate precautions. The station operator and others in the shack who know transmissions are occurring are in the controlled environment. Higher MPE limits apply because these persons can monitor and manage their exposure.

Uncontrolled (general public) exposure: Applies to persons who may not be aware of or cannot control their exposure — neighbors, passersby, persons in adjacent buildings. The uncontrolled MPE limits are five times lower (more restrictive) than the controlled limits. Your neighbors cannot walk out of the path of your RF field. The FCC treats their exposure accordingly.

The MPE limits also vary by frequency. At 30 MHz, the controlled MPE limit is 1.0 mW/cm². At 300 MHz (near body resonance), the controlled limit drops to 1.0 mW/cm² and the uncontrolled limit drops to 0.2 mW/cm². The limits are set at their most restrictive in the VHF/UHF range where body absorption is greatest.

When an RF Exposure Evaluation is Required

Not every amateur station must perform a detailed RF exposure evaluation. The FCC has established power thresholds by band — stations operating below these thresholds are categorically excluded from the evaluation requirement (47 CFR §97.13(c)(1)). Stations operating above the thresholds must evaluate their RF exposure and ensure compliance.

The threshold power levels vary by band. As a practical matter, most 100-watt HF stations with antennas at normal heights easily comply with MPE limits at typical operator and public distances. However, the evaluation is still required if you exceed the threshold, and you must be able to demonstrate compliance. The FCC provides an online RF exposure calculator that walks you through the evaluation.

Duty Cycle — Why It Matters

RF exposure is time-averaged over a 6-minute period for the controlled environment (30 minutes for uncontrolled). The duty cycle of your operating mode significantly affects your actual average exposure.

Because SSB voice duty cycle is lower than digital modes, a 100-watt SSB station may comply with MPE limits at a given antenna distance that a 100-watt FT8 station does not. When operating digital modes continuously, use the most conservative duty cycle assumptions in your evaluation.

Practical RF Safety Measures

• Mount antennas as far as practical from areas where people spend time — the power density decreases with the square of the distance, so doubling the distance reduces exposure to one-quarter
• Do not operate VHF/UHF antennas at close range without evaluating exposure first — these frequencies are near body resonance where absorption is highest
• Never touch, handle, or stand close to a transmitting antenna
• Reduce power when testing or adjusting antennas at close range
• Inform family members of RF exposure considerations, particularly regarding antennas mounted on or near the house

Lightning and Antenna Safety

The Threat

An outdoor antenna system is a conductor elevated above the surrounding terrain and connected to equipment inside your building. During a thunderstorm, this is precisely the path that lightning seeks. A direct lightning strike to an antenna tower or wire delivers hundreds of millions of volts and tens of thousands of amperes in microseconds. No lightning arrestor in existence will survive a direct strike. Arrestors and surge protectors protect against nearby strikes and induced surges — they are not protection against a direct strike.

Physical Disconnection — The Only Real Protection

The only reliable protection against lightning damage to your equipment — and the only protection that also protects you personally — is physical disconnection of all antenna feedlines from your equipment before and during electrical storms. This means:

• Disconnect the coax from the back of the transceiver
• Disconnect any control cables connected to antenna switches, rotators, or remote systems
• Disconnect the AC power from all station equipment if severe lightning is close
• Do not operate the station during an electrical storm in the local area

Lightning arrestors (gas-discharge tubes, spark gaps, or semiconductor-based surge protectors) installed at the entry point of feedlines into the building reduce the risk from nearby strikes and induced surges on the feedline. They are a useful supplement to a proper grounding system. They are not a substitute for physical disconnection. An operator who relies on an arrestor and leaves equipment connected during a storm is gambling with both their equipment and their life.

Grounding System for Lightning Protection

A proper station grounding system provides a low-impedance path for lightning energy to reach earth ground without traveling through your equipment. Key elements:

• Ground rod: One or more 8-foot copper-clad steel ground rods driven into the earth at the base of any tower or mast, and at the building entry point for feedlines. Multiple rods bonded together with heavy conductor improve the ground impedance.
• Single-point ground: All feedlines, control cables, and power entry points should be bonded at a single ground point where they enter the building. This prevents lightning- induced current from flowing from one cable to another through your equipment.
• Heavy conductor: Use #4 AWG or larger copper conductor for ground connections. The conductor inductance at lightning frequencies matters — keep ground conductors short and straight. A long, coiled ground wire is worse than a short straight wire of smaller gauge.
• Lightning arrestors: Mount gas-discharge or semiconductor surge arrestors at the building entry point, with the arrestor case bonded to the entry ground point.

A proper grounding system reduces the risk of equipment damage from nearby strikes and improves the chances that a direct strike to your antenna will be conducted safely to ground rather than through your building's wiring. It does not eliminate the risk of equipment damage from a direct strike.

Tower and Antenna Structure Safety

Fall Protection — Non-Negotiable

Falls from antenna towers are one of the leading causes of serious injury and death in amateur radio. Every year, operators who are experienced, competent, and who have climbed towers many times before are killed by falls. The cause is almost always the same: failure to use proper fall protection equipment.

Required equipment for any tower climb:

• Full-body harness: A properly fitted ANSI/OSHA-rated full-body harness distributes fall arrest forces across the hips, chest, and shoulders. A simple belt or waist harness is not acceptable for fall arrest — the force of a fall can cause fatal internal injuries when arrested by a waist belt alone.
• Shock-absorbing lanyard: A double-lanyard system allows you to maintain connection to the tower at all times while moving. With two lanyards, one is always attached while the other is being repositioned. The lanyard must include a shock absorber that limits arrest force to safe levels.
• Hard hat: Protects against dropped tools and objects from above.
• Non-slip footwear: Wet steel tower members are extremely slippery.

Conditions When You Must Not Climb

Some conditions make tower climbing unacceptably dangerous regardless of the equipment you are wearing:

• During electrical storms or when storms are approaching: A metal tower is an excellent lightning conductor. Do not be on it when lightning is in the area.
• During high winds (generally above 20 mph): Wind load on your body at tower height is significant. Gusts can cause you to lose footing or grip unexpectedly. Antenna work in wind is also harder to control, increasing the risk of dropped tools or antennas swinging unexpectedly.
• When ice or frost is on the tower: Ice-covered steel tower rungs and braces are extraordinarily slippery. Even with good footwear, maintaining grip and footing on an iced tower is extremely difficult.
• When alone: Never climb a tower when no one is present at the base. If you are injured at height and cannot call for help, you may be there for a long time. The person at the base is also your tool handler, your emergency contact, and your first responder if something goes wrong.
• When fatigued: Physical and mental fatigue increase error rates and slow reaction times. Do not climb when you are tired.

Antenna Structures Near Power Lines

An antenna wire or tower that falls and contacts an overhead power line creates a lethal hazard. The FCC and OSHA both address this. The basic rules:

• No antenna or antenna support should be installed in a location where it could fall and contact overhead power lines
• The minimum safe distance from a power line is the total height of the structure plus a safety margin
• Never install antennas by hand near overhead power lines — use non-conductive rope to throw antenna supports; never use metal wire near power lines
• If an antenna wire falls across a power line, do not attempt to remove it yourself. Contact the power company. This is their job and they have the equipment to do it safely.

Battery Safety

Lead-Acid Battery Hazards

Lead-acid batteries present two distinct hazards that new operators frequently underestimate:

Explosive hydrogen gas: Charging a lead-acid battery (flooded cell type) causes electrolysis that releases hydrogen gas from the electrolyte. Hydrogen is explosive at concentrations as low as 4% in air. In an enclosed space, charging a large battery bank can accumulate explosive concentrations of hydrogen in minutes. A single spark — from a tool, a switch, static electricity, or a loose connection — can ignite the gas. The explosion can be violent enough to shatter the battery case and spray sulfuric acid.

Always charge lead-acid batteries in well-ventilated areas. If you are charging multiple large batteries in a confined space (a garage, a vehicle, an equipment shelter), ensure active ventilation. Do not leave connections disconnected and reconnected near a charging battery — the arc from reconnecting a cable near a charging battery is a potential ignition source.

Sulfuric acid: The electrolyte in a flooded lead-acid battery is dilute sulfuric acid. Contact with skin or eyes requires immediate flushing with large amounts of water. When working with flooded lead-acid batteries, wear safety glasses or goggles. An exploding battery can spray electrolyte at high velocity, and the one area where you absolutely cannot afford a chemical burn is your eyes. This is not optional equipment when working with lead-acid batteries.

Short-circuit current: A large lead-acid battery can deliver hundreds to thousands of amperes into a short circuit. A tool dropped across the battery terminals will immediately vaporize metal at the point of contact, potentially causing burns and fire. Keep one battery terminal covered when working near a battery. Remove metal jewelry (watches, rings, bracelets) before working with high-capacity batteries.

Lithium Battery Hazards

Lithium Iron Phosphate (LiFePO4) batteries are safer than other lithium chemistries but still present hazards:

• Charging below 0°C (32°F) causes internal damage and potential safety hazards (lithium plating on the anode)
• Overcharging with the wrong charger can cause cell damage and, in severe cases, venting
• A damaged BMS (Battery Management System) can allow overcharge or over-discharge conditions that damage the cells
• Physically damaged lithium cells should be removed from service immediately and disposed of properly — damaged cells can develop internal short circuits that cause thermal runaway

Part 2 — Exam Coverage

The G0 subelement covers electrical and RF safety as tested in the 2023–2027 FCC General Class question pool. All pool questions are covered below. This is the most important module to know cold — not just for the exam but because the answers describe things that keep you alive.

Key Facts to Memorize for the Exam

• RF exposure: Two environments — controlled and uncontrolled; uncontrolled limits are 5x more restrictive
• RF evaluation threshold: Required when operating above specified power levels per band (47 CFR §97.13)
• Duty cycle: Digital modes (FT8, RTTY) have highest duty cycle; SSB voice is lower; matters for exposure averaging
• Most susceptible tissues: Eyes and testes (limited blood flow for heat dissipation)
• One-hand rule: Keep one hand behind your back when working on energized circuits above 30V
• Capacitor discharge: Always discharge filter capacitors before working on power supplies
• Bleeder resistor: Discharges capacitors after power removed; safety device in power supplies
• Lead-acid batteries: Produce explosive hydrogen gas when charging; use ventilation; wear goggles
• Power lines: Never install an antenna where it could contact a power line if it falls
• Tower climbing: Always use full-body harness and double lanyard; never climb alone; never in storms or high wind
• Lightning: Disconnect feedlines during electrical storms; arrestors supplement but do not replace physical disconnection
• Grounding: Single-point ground at building entry; heavy conductor; bond all entry cables to ground

Practice Questions — G0 Complete Pool Coverage

G0A — RF Safety Principles and Evaluation

G0B — Electrical Safety

Part 3 — External Resources

RF Safety

• FCC RF Safety Information — The FCC's official RF safety page including the online exposure calculator for amateur radio stations. Use this to perform your required evaluation. Free, authoritative, and designed specifically for amateur radio use.
  fcc.gov RF Safety
• ARRL RF Exposure Calculator — The ARRL provides an online RF exposure calculator that simplifies the evaluation process for common amateur radio antenna configurations.
  arrl.org/rf-exposure-calculator
• OET Bulletin 65 Supplement B (FCC) — The FCC's detailed guidance document for performing RF exposure evaluations for amateur radio stations. The authoritative reference for understanding the evaluation methodology.
  fcc.gov/oet/rfsafety

Electrical Safety

• ARRL Safety Information — The ARRL maintains safety information covering electrical safety, tower climbing, lightning protection, and RF exposure for amateur operators.
  arrl.org/safety
• OSHA Electrical Safety — OSHA's guidance on electrical safety applies to amateur radio station work. The hand safety rules, grounding requirements, and lockout/tagout procedures described here are directly applicable to station construction and maintenance.
  osha.gov/electrical

Tower Safety

• ARRL Tower Safety — The ARRL provides specific guidance on antenna tower climbing safety including equipment requirements, pre-climb checklists, and hazard identification.
  arrl.org/tower-safety
• Rohn Products Tower Safety Guide — Rohn, the largest manufacturer of amateur radio towers in North America, publishes installation and safety guidelines for their tower products. These apply broadly to tower work of any kind.
  rohnnet.com

Lightning Protection

• PolyPhaser/Transtector Lightning Protection — The manufacturer of the most widely used lightning arrestors in amateur radio. Their application notes explain grounding system design, single-point entry, and arrestor selection for amateur stations.
  transtector.com
• W8JI Grounding and Lightning Protection — Tom Rauch W8JI's detailed technical articles on lightning protection grounding for amateur radio stations. Covers single- point ground design and bonding in practical depth.
  w8ji.com

Exam Preparation

• ARRL General Class License Manual — Standard exam study guide covering all G0 subelement topics.
  ARRL Store
• No-Nonsense General Class Study Guide (KB6NU) — Free PDF covering all G0 pool questions with concise explanations.
  kb6nu.com/study-guides
• HamStudy.org — G0 questions on MPE evaluation requirements and RF exposure calculations are among those most commonly missed. Use subelement tracking to identify gaps before the exam.
  hamstudy.org
• QRZ.com Practice Exams — Full simulated General Class exams from the actual pool. Take at least ten full practice exams and score above 85% consistently before scheduling your exam session.
  qrz.com/hamtest

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