Technician · correct answers only, in question-pool order.
Low voltage does not mean low available current. A storage battery can deliver enormous current into a short circuit.
Current through the body can injure in several ways at once: it can heat tissue, interfere with normal electrical activity in cells, and trigger involuntary muscle contractions.
In standard U.S. 120-volt branch wiring, black insulation identifies the energized or “hot” conductor.
A fuse is a sacrificial overcurrent device. If current exceeds its rating long enough, it opens the circuit and removes power before wiring or equipment is damaged.
Replacing a 5-amp fuse with a 20-amp fuse defeats the intended protection. Wiring or components may overheat dangerously before the larger fuse opens.
Electrical-shock protection is layered: use grounded three-wire cords, bond AC-powered equipment to a common safety ground, and discharge high-voltage capacitors before working inside equipment.
A lightning arrester should be mounted at the building entry point on a grounded panel so surge energy has a short path to the grounding system before the feed line continues indoors.
The protective device belongs in series with the hot conductor. Opening the hot lead removes the energized source from the protected circuit.
Separate ground rods can rise to different voltages during a lightning event. Bonding them together reduces dangerous voltage differences between grounding systems.
High charge or discharge rates can create damaging heat and may cause gases to be released, depending on battery chemistry and condition.
Large capacitors can retain dangerous voltage after AC power is removed, so “off” does not necessarily mean electrically safe.
Meters, probes, insulation, and category ratings all matter when working around hazardous voltage.
Lightning current should have a short, direct route to ground. Long runs and unnecessary bends increase the impedance of the grounding path.
Safe tower climbing requires training, an approved climbing harness, and continuous proper tie-off. None of those precautions substitutes for the others.
Tower work combines fall, mechanical, and electrical hazards. A qualified helper or observer is an essential part of safe work practices.
Before erecting a tower or antenna, identify every nearby overhead power conductor and keep the entire structure and work area safely clear of it.
Vibration can slowly rotate a turnbuckle and change guy-line tension. A safety wire prevents the turnbuckle from loosening.
Plan for the antenna or support to fall in the worst plausible direction. Clearance must protect against accidental contact, not just normal upright spacing.
A crank-up tower can move unexpectedly. It should not be climbed unless it is fully retracted or secured with proper mechanical locking devices.
A tower needs a low-impedance grounding system. Separate eight-foot rods at the legs, bonded to the tower and to one another, provide multiple paths into the earth.
Utility poles carry hazardous power conductors. An attached amateur antenna could contact those conductors directly or during failure or maintenance.
Lightning is a fast surge, so sharp bends add unwanted impedance and can encourage flashover. Grounding conductors should use smooth, gradual routing.
Tower and antenna grounding must satisfy the electrical rules that apply where the installation is located.
Amateur radio signals are non-ionizing radiation. Their photons do not carry enough energy to ionize atoms the way X-rays or gamma rays can.
RF exposure limits vary with frequency because the body does not absorb RF energy equally at all frequencies. Among these choices, 50 MHz has the lowest maximum permissible exposure.
At a 50 percent duty cycle, the transmitter is on only half the time. For the same average exposure, the allowable instantaneous power density can therefore be twice as high as at 100 percent duty cycle.
RF exposure depends on the strength of the field and on how a person is positioned relative to it. Frequency, power, distance, and antenna radiation pattern all matter.
Human tissue couples to RF fields differently as frequency changes, so the amount of energy absorbed by the body is frequency-dependent.
FCC compliance can be demonstrated by accepted calculations, computer modeling, or calibrated field-strength measurements.
An energized antenna can develop RF voltage and current high enough to heat tissue at the point of contact, producing an RF burn.
Moving an antenna can increase the distance between people and strong RF fields or redirect the field away from occupied areas.
Changes to transmitter power, feed line, antenna, location, or other RF-system details can change exposure levels. The station should be re-evaluated whenever such a change could affect compliance.
RF exposure limits are based on average exposure over time. Duty cycle tells you how much of that averaging period the transmitter is actually producing RF.
Duty cycle is simply the fraction of the averaging period during which the transmitter is actually transmitting.
RF is non-ionizing: individual RF photons do not carry enough energy to produce the ionization and direct DNA damage associated with radioactive or other ionizing radiation.
The station licensee is responsible for operating the station within FCC RF-exposure limits and for ensuring that people are not exposed above those limits.