General Course, Module 10: Safety at HF Power

10.1RF Exposure, Now That You Have Real Power

The Technician foundation stands: RF is non-ionizing, and its effect on the body is heating tissue. What changes at General is that your power and your antennas got serious, so the evaluation becomes personal engineering instead of a checkbox.

Whether a signal exceeds the maximum permissible exposure (MPE) limits depends on its frequency, its power density, and its duty cycle. All of these, the same three-legged stool from Technician, now supporting 100-watt legs. The evaluation methods also carry over intact: calculation per FCC OET Bulletin 65, computer modeling, or measurement with calibrated field-strength equipment. All acceptable.

The concepts that do the heavy lifting at HF power:

• Duty cycle remains the percentage of time transmitting during the averaging period, and its practical consequence is stated plainly: a lower duty cycle permits greater power levels for the same average exposure. A CW conversation at 50 percent duty and low key-down density exposes far less than the same power of key-down FT8, which is Module 6's finals-cooking warning wearing its safety hat.
• Time averaging is the principle underneath: RF exposure is averaged over time, because the hazard is cumulative heating, not instantaneous fields. Bodies, like transistors, care about average power.

The obligations, and they are yours:

• Perform the routine station evaluation to determine whether your station complies with MPE limits, and repeat it when anything in the transmitter or antenna system changes.
• If the evaluation shows exposure limits exceeded where people can be, take action to prevent human exposure: relocate the antenna, reduce power, restrict access to the area, or fence the time people spend there. Two specific versions the exam names: if a directional antenna's main lobe would exceed limits at a neighbor's location, ensure the antenna cannot be pointed in their direction; and an indoor transmitting antenna demands verifying that MPE limits are not exceeded in occupied areas, because indoors, everywhere is the near field. The fix is required, not suggested.
• Before working on an antenna, make sure transmitters that feed it cannot transmit: powered down, disconnected, and everyone in the household briefed. An antenna under maintenance is an antenna off the air, no exceptions, which also finishes the RF burn story from Technician: the burn happens when the antenna and the hand meet during transmission, so the rule ensures they never can.

10.2Wiring, Generators, and the Tower, at Full Scale

The electrical rules scale up from Technician with numbers attached.

Wiring by the book:

• Fuses and circuit breakers go in series with the hot conductor only, the Technician rule unchanged and worth repeating forever.
• Wire gauge now has values: AWG 12 for a 20-ampere circuit, AWG 10 for 30 amperes, and the rule runs both directions: AWG 14 wire must be protected by a fuse or breaker of no more than 15 amperes. Wire is rated by what warms it, and the fuse from Technician Module 10 is still protecting the wire, not the radio.
• Inside equipment, two capacitor disciplines: bleeder resistors (Module 5) discharge supply capacitors at power-off, and before working inside high-voltage equipment you verify the discharge yourself with a meter rated for the job. Interlocks, whose purpose is to remove dangerous voltages when the cabinet is opened, are respected, never defeated.
• One bench-habit rule the exam likes: after soldering, wash your hands. Lead-tin solder is a skin-contact and hand-to-mouth hazard, and the cure costs thirty seconds of soap.

Generators power the emergency station and bring two killers to manage. The first is carbon monoxide: a generator runs outdoors, well away from building openings, windows, doors, and vents, full stop. The second is invisible from your side of the meter: when a generator powers your house, you must disconnect the incoming utility power feed first. Backfeeding the grid can energize "dead" lines and kill the lineworker restoring your neighborhood, which makes the transfer switch the most important safety device in your emergency power plan.

The tower repeats the Technician discipline with the crew formalized:

• Climbing gear, harness and lanyards, is inspected before each use, and the climber maintains 100 percent tie-off at all times, with tools raised on a line rather than carried in hand.
• The ground crew is part of the safety system: anyone standing below wears a hard hat and safety glasses the entire time someone is aloft. Dropped wrenches obey Module 10 of the Technician course: gravity is also a hazard.
• Grounding at full scale: each tower leg gets its own ground rod, all bonded together, with lightning conductors run short and direct, avoiding sharp bends (lightning, all rise-time and no patience, treats a sharp bend as an inductor and jumps it), and lightning arrestors on a grounded panel where the feed lines enter the building. Every element of that sentence appeared somewhere earlier in your training; here it assembles into one drawing, which is exactly what your capstone's station-design documentation asks you to produce.

You Made It, Again

Ten modules, ten subelements, all 35 questions' worth of General material, taught the same way the Technician course taught: story first, exam anchor always, hands on wherever hands fit.

Ray's send-off is shorter this time, because you need less. "Book the exam. Sign '/AG' the same afternoon. Then get the capstone done while the bands are open: three bands, two modes, one DX contact, on an antenna you built. And start noticing which new hams at the club could use an Elmer, because the next course asks you to become one."

Next steps:

• Practice exams until the misses stop clustering. Reread sections, not answer keys.
• Complete the General Skills Track and the 24-hour station capstone from the curriculum page.
• When the Extra segments at the band edges start taunting you, and they will, the Extra course is next.

© 2026 Anthony Pelfanio, K4DIA. All rights reserved.