Technicians Exam-Electrical and RF Safety

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rledwith
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Technicians Exam-Electrical and RF Safety
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Amateur Radio Technicians Exam - T0 Electrical and RF Safety
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  1. T0A01 Which is a commonly accepted value for the lowest voltage that can cause a dangerous electric shock?
    A. 12 volts
    B. 30 volts
    C. 120 volts
    D. 300 volts
    • B. 30 volts
    • Low-voltage power supplies may seem safe, but even battery-powered equipment should be treated with care. The minimum voltage that is considered a shock hazard to humans is 30 volts. You should respect even low voltages, taking appropriate steps to avoid contact. Lower-voltage systems such as storage batteries are quite capable of causing a fire hazard, so even without being a shock hazard, there are plenty of reasons to treat them with care. [Ham Radio License Manual, page 9-2]
  2. T0A02 How does current flowing through the body cause a health hazard?
    A. By heating tissue
    B. It disrupts the electrical functions of cells
    C. It causes involuntary muscle contractions
    D. All of these choices are correct
    • D. All of these choices are correct
    • Burns caused by dc current or low-frequency ac current are a result of resistance to current in the skin, either through it to the body’s interior or along it from point to point. The current creates heat and that’s what results in the burn. Electrical current through the body can disrupt the electrical function of cells. Currents of more than a few mA can also cause involuntary muscle contractions, which leads to the jerking and jumping image on TV and in the movies. No joking matter, muscle spasms can cause falls and sudden large movements. The sudden pulling back of an outstretched hand or finger that comes in contact with an energized conductor is a result of arm muscles contracting. [Ham Radio License Manual, page 9-2]
  3. T0A03 What is connected to the green wire in a three-wire electrical AC plug?
    A. Neutral
    B. Hot
    C. Safety ground
    D. The white wire
    • C. Safety ground
    • State and national electrical-safety codes require the three-wire power cords on many 120-V tools and appliances. Power supplies and station equipment use similar connections. Two of the conductors (the “hot” and the “neutral” wires) power the device. The third conductor (the safety ground wire) connects to the metal frame of the device. The “hot” wire is usually black or red. The “neutral” wire is white. The frame/ground wire is green or sometimes bare. See Figure T0-1. [Ham Radio License Manual, page 9-4]
  4. T0A04 What is the purpose of a fuse in an electrical circuit?
    A. To prevent power supply ripple from damaging a circuit
    B. To interrupt power in case of overload
    C. To limit current to prevent shocks
    D. All of these choices are correct
    • B. To interrupt power in case of overload
    • A fuse consists of a thin strip of metal that melts at relatively low temperatures. Current flow causes the metal to heat up and when too much current flows, the metal melts, breaking the circuit and interrupting power. [Ham Radio License Manual, page 3-11]
  5. T0A05 Why is it unwise to install a 20-ampere fuse in the place of a 5-ampere fuse?
    A. The larger fuse would be likely to blow because it is rated for higher current
    B. The power supply ripple would greatly increase
    C. Excessive current could cause a fire
    D. All of these choices are correct
    • C. Excessive current could cause a fire
    • Never replace a fuse or circuit breaker with one rated for a larger current, since that allows more current to flow in response to a fault in the equipment. The higher current could overheat wires and cause a fire. Determine what problem caused the fuse to blow and repair it so that higher current does not make the damage worse or destroy the equipment entirely. [Ham Radio License Manual, page 3-11]
  6. T0A06 What is a good way to guard against electrical shock at your station?
    A. Use three-wire cords and plugs for all AC powered equipment
    B. Connect all AC powered station equipment to a common safety ground
    C. Use a circuit protected by a ground-fault interrupter
    D. All of these choices are correct
    • D. All of these choices are correct
    • The best way to protect against electrical shock is to make sure that each part of your station as at the same potential or voltage. That potential should, of course, be ground potential. You’ll want to make sure that you have a common safety ground, meaning that all grounds should be connected together. Three-wire cords and plugs make sure the equipment enclosures are connected to the safety ground. A ground-fault interrupter detects current imbalance between the hot and neutral wires, indicating a short circuit to the safety ground, and turns off power to the circuit. [Ham Radio License Manual, page 9-3]
  7. T0A07 Which of these precautions should be taken when installing devices for lightning protection in a coaxial cable feedline?
    A. Include a parallel bypass switch for each protector so that it can be switched out of the circuit when running high power
    B. Include a series switch in the ground line of each protector to prevent RF overload from inadvertently damaging the protector
    C. Keep the ground wires from each protector separate and connected to station ground
    D. Ground all of the protectors to a common plate which is in turn connected to an external ground
    • D. Ground all of the protectors to a common plate which is in turn connected to an external ground
    • Even though amateur antennas and towers are struck no more frequently than tall trees or other nearby structures, it is wise to take some precautionary steps. This is especially true for stations in areas with frequent severe weather and lightning. Lightning protection is intended to provide fire protection for your home since most of the damage to a home resulting from a lightning strike is from fire. Starting at your antennas, all towers, masts, and antenna mounts should be grounded according to your local building codes. This is done at the base, or in the case of roof mounts, though a large-diameter wire to a ground rod. Ground connections should be as short and direct as possible — avoid sharp bends. Where cables enter the house, use lightning arrestors grounded to a common plate that is in turn connected to a nearby external ground such as a ground rod. [Ham Radio License Manual, page 9-4]
  8. T0A08 What is one way to recharge a 12-volt lead-acid station battery if the commercial power is out?
    A. Cool the battery in ice for several hours
    B. Add acid to the battery
    C. Connect the battery to a car’s battery and run the engine
    D. All of these choices are correct
    • C. Connect the battery to a car’s battery and run the engine
    • Your vehicle is an excellent source of backup power. It can easily recharge a storage battery. Smaller batteries should be carefully monitored for excessive temperature when charging from a vehicle since there is no circuitry to limit charging current. Follow standard vehicle safety practices when using your car to recharge batteries. [Ham Radio License Manual, page 5-17]
  9. T0A09 What kind of hazard is presented by a conventional 12-volt storage battery?
    A. It emits ozone which can be harmful to the atmosphere
    B. Shock hazard due to high voltage
    C. Explosive gas can collect if not properly vented
    D. All of these choices are correct
    • C. Explosive gas can collect if not properly vented
    • Storage batteries pack a lot of energy into a small volume, but with that energy comes the need to treat them carefully. The liquid acid in the battery is extremely corrosive and will eat holes in anything organic (including your clothes and skin!) During charging, hydrogen gas is given off by the battery and can be explosive if there is no ventilation to disperse it. Most of all, a short circuit in a storage battery circuit can draw hundreds of amps from the battery, melting wires and terminals and igniting insulation in a hurry! Take special care to keep tools from accidentally shorting across the battery terminals! [Ham Radio License Manual, page 5-17]
  10. T0A10 What can happen if a lead-acid storage battery is charged or discharged too quickly?
    A. The battery could overheat and give off flammable gas or explode
    B. The voltage can become reversed
    C. The “memory effect” will reduce the capacity of the battery
    D. All of these choices are correct
    • A. The battery could overheat and give off flammable gas or explode
    • Trying to get energy into or out of any battery too quickly can cause it to overheat. Excessive charging can cause hydrogen gas to build up faster than the battery can vent it to the outside air. Overheating is particularly dangerous with storage batteries, since they hold so much energy. Use a battery charger that is designed to work with storage batteries and keep the load on the battery to within the manufacturer’s specifications. [Ham Radio License Manual, page 5-17]
  11. T0A11 Which of the following is good practice when installing ground wires on a tower for lightning protection?
    A. Put a loop in the ground connection to prevent water damage to the ground system
    B. Make sure that all bends in the ground wires are clean, right angle bends
    C. Ensure that connections are short and direct
    D. All of these choices are correct
    • C. Ensure that connections are short and direct
    • Even though amateur antennas and towers are struck no more frequently than tall trees or other nearby structures, it is wise to take some precautionary steps. This is especially true for stations in areas with frequent severe weather and lightning. Lightning protection is intended to provide fire protection for your home since most of the damage to a home resulting from a lightning strike is from fire. Starting at your antennas, all towers, masts, and antenna mounts should be grounded according to your local building codes. This is done at the base, or in the case of roof mounts, though a large-diameter wire to a ground rod. Ground connections should be as short and direct as possible — avoid sharp bends. Where cables enter the house, use lightning arrestors grounded to a common plate that is in turn connected to a nearby external ground such as a ground rod. [Ham Radio License Manual, page 9-4]
  12. T0A12 What kind of hazard might exist in a power supply when it is turned off and disconnected?
    A. Static electricity could damage the grounding system
    B. Circulating currents inside the transformer might cause damage
    C. The fuse might blow if you remove the cover
    D. You might receive an electric shock from stored charge in large capacitors
    • D. You might receive an electric shock from stored charge in large capacitors
    • A capacitor is designed to store charge, so it should not be a surprise that a capacitor can remain charged even after power is removed. It is good practice to place bleeder resistors across large capacitors to slowly allow the charge to dissipate. Never assume that capacitors, particularly those in high-voltage circuits, are discharged. Measure them with a voltmeter first or use a grounding stick to discharge them. [Ham Radio License Manual, page 9-3]
  13. T0A13 What safety equipment should always be included in home-built equipment that is powered from120V AC power circuits?
    A. A fuse or circuit breaker in series with the AC “hot” conductor
    B. An AC voltmeter across the incoming power source
    C. An inductor in series with the AC power source
    D. A capacitor across the AC power source
    • A. A fuse or circuit breaker in series with the AC “hot” conductor
    • If you decide to run new wiring for your station as it grows, either have a licensed electrician do the wiring or inspect it. Be sure to follow the hot-black (occasionally red)/neutral-white/ground-green or bare wiring standard. Use cable and wire sufficiently rated for the expected current load. Use the proper size fuses and circuit breakers. If you build your own equipment and power it from the ac lines, be sure to always install a fuse or circuit breaker in series with the ac hot conductor. [Ham Radio License Manual, page 9-4]
  14. T0B01 When should members of a tower work team wear a hard hat and safety glasses?
    A. At all times except when climbing the tower
    B. At all times except when belted firmly to the tower
    C. At all times when any work is being done on the tower
    D. Only when the tower exceeds 30 feet in height
    • C. At all times when any work is being done on the tower
    • A piece of hardware or a tool will be traveling 40 mph by the time it falls 60 feet! Ouch! Whenever the crew is working on the tower, wear your protective gear — even if you are near the base of the tower. If a falling object hits the tower or a guy wire, it can bounce a long way. Try to stay out from under the crew at work at the top. And while you’re at it, remember the sun block! [Ham Radio License Manual, page 9-13]
  15. T0B02 What is a good precaution to observe before climbing an antenna tower?
    A. Make sure that you wear a grounded wrist strap
    B. Remove all tower grounding connections
    C. Put on a climbing harness and safety glasses
    D. All of the these choices are correct
    • C. Put on a climbing harness and safety glasses
    • Make sure your climbing harness and glasses and hard hat are in good condition — then use them! Climb slowly, with a lanyard around the tower. It’s not a race, so take your time. Once at the top, work slowly, thinking out each move before you make it. Have a backup plan and never work on a tower without a ground crew or someone to keep an eye on you. [Ham Radio License Manual, page 9-13]
  16. T0B03 Under what circumstances is it safe to climb a tower without a helper or observer?
    A. When no electrical work is being performed
    B. When no mechanical work is being performed
    C. When the work being done is not more than 20 feet above the ground
    D. Never
    • D. Never
    • Having a ground crew is important; avoid climbing alone whenever possible because it’s never safe. If you do climb alone, take along a handheld radio so that you can call for help if needed. [Ham Radio License Manual, page 9-13]
  17. T0B04 Which of the following is an important safety precaution to observe when putting up an antenna tower?
    A. Wear a ground strap connected to your wrist at all times
    B. Insulate the base of the tower to avoid lightning strikes
    C. Look for and stay clear of any overhead electrical wires
    D. All of these choices are correct
    • C. Look for and stay clear of any overhead electrical wires
    • If power lines ever come into contact with your antenna, you could be electrocuted. The only safe place to install an antenna tower is in a location that is well clear of any power lines. Before you put up a tower, look for any overhead electrical wires. Make sure that the tower is installed where there is no possibility of contact between the lines and the tower if the guy wires should ever break or the tower fall. [Ham Radio License Manual, page 9-12]
  18. T0B05 What is the purpose of a gin pole?
    A. To temporarily replace guy wires
    B. To be used in place of a safety harness
    C. To lift tower sections or antennas
    D. To provide a temporary ground
    • C. To lift tower sections or antennas
    • A gin pole is a temporary mast used to lift materials such as antennas or tower sections so that you do not have to hoist things directly. This is much safer than a direct lift and supports the materials while you work on them. [Ham Radio License Manual, page 9-13]
  19. T0B06 What is the minimum safe distance from a power line to allow when installing an antenna?
    A. Half the width of your property
    B. The height of the power line above ground
    C. 1/2 wavelength at the operating frequency
    D. So that if the antenna falls unexpectedly, no part of it can come closer than 10 feet to the power wires
    • D. So that if the antenna falls unexpectedly, no part of it can come closer than 10 feet to the power wires
    • Ten feet of separation is the minimum amount for safety if the tower and antenna fall directly towards the power lines. Figure the separation from the very top of the antenna or with the antenna oriented so that it is closest to the power lines. Allow for more separation whenever possible. [Ham Radio License Manual, page 9-12]
  20. T0B07 Which of the following is an important safety rule to remember when using a crank-up tower?
    A. This type of tower must never be painted
    B. This type of tower must never be grounded
    C. This type of tower must never be climbed unless it is in the fully retracted position
    D. All of these choices are correct
    • C. This type of tower must never be climbed unless it is in the fully retracted position
    • Climbing a crank-up tower places your hands and feet between rungs and braces that can do a lot of damage if the tower sections slip or a cable breaks. Not only should you be sure the tower is fully nested, but also place a safety block such as piece of pipe or a 2-by-4 between the rungs to prevent movement. [Ham Radio License Manual, page 9-13]
  21. T0B08 What is considered to be a proper grounding method for a tower?
    A. A single four-foot ground rod, driven into the ground no more than 12 inches from the base
    B. A ferrite-core RF choke connected between the tower and ground
    C. Separate eight-foot long ground rods for each tower leg, bonded to the tower and each other
    D. A connection between the tower base and a cold water pipe
    • C. Separate eight-foot long ground rods for each tower leg, bonded to the tower and each other
    • Don’t confuse a safety ground with an RF ground! A tower’s safety ground is intended to conduct any lightning energy to the earth, reducing the amount traveling along your feed lines. Grounding each leg of the tower balances lightning currents — a weak ground will encourage more energy to flow along your feed lines. It also dissipates the charge into the ground as widely as possible. [Ham Radio License Manual, page 9-12]
  22. T0B09 Why should you avoid attaching an antenna to a utility pole?
    A. The antenna will not work properly because of induced voltages
    B. The utility company will charge you an extra monthly fee
    C. The antenna could contact high-voltage power wires
    D. All of these choices are correct
    • C. The antenna could contact high-voltage power wires
    • Never attach an antenna or guy wire to a utility pole, since a mechanical failure could result in contact with high-voltage lines. [Ham Radio License Manual, page 9-12]
  23. T0B10 Which of the following is true concerning grounding conductors used for lightning protection?
    A. Only non-insulated wire must be used
    B. Wires must be carefully routed with precise right-angle bends
    C. Sharp bends must be avoided
    D. Common grounds must be avoided
    • C. Sharp bends must be avoided
    • Even though amateur antennas and towers are struck no more frequently than tall trees or other nearby structures, it is wise to take some precautionary steps. This is especially true for stations in areas with frequent severe weather and lightning. Lightning protection is intended to provide fire protection for your home since most of the damage to a home resulting from a lightning strike is from fire. Starting at your antennas, all towers, masts, and antenna mounts should be grounded according to your local building codes. This is done at the base, or in the case of roof mounts, though a large-diameter wire to a ground rod. Ground connections should be as short and direct as possible — avoid sharp bends. Where cables enter the house, use lightning arrestors grounded to a common plate that is in turn connected to a nearby external ground such as a ground rod. [Ham Radio License Manual, page 9-4]
  24. T0B11 Which of the following establishes grounding requirements for an amateur radio tower or antenna?
    A. FCC Part 97 Rules
    B. Local electrical codes
    C. FAA tower lighting regulations
    D. Underwriters Laboratories’ recommended practices
    • B. Local electrical codes
    • Even though amateur antennas and towers are struck no more frequently than tall trees or other nearby structures, it is wise to take some precautionary steps. This is especially true for stations in areas with frequent severe weather and lightning. Lightning protection is intended to provide fire protection for your home since most of the damage to a home resulting from a lightning strike is from fire. Starting at your antennas, all towers, masts, and antenna mounts should be grounded according to your local building codes. This is done at the base, or in the case of roof mounts, though a large-diameter wire to a ground rod. Ground connections should be as short and direct as possible — avoid sharp bends. Where cables enter the house, use lightning arrestors grounded to a common plate that is in turn connected to a nearby external ground such as a ground rod. [Ham Radio License Manual, page 9-4]
  25. T0C01 What type of radiation are VHF and UHF radio signals?
    A. Gamma radiation
    B. Ionizing radiation
    C. Alpha radiation
    D. Non-ionizing radiation
    • D. Non-ionizing radiation
    • Radio and lower frequency waves are classified as non-ionizing radiation because the frequency is too low for them to ionize atoms, no matter how intense the power density of the wave may be. The frequency of ionizing radiation must be higher than that of visible light — ultraviolet, X-rays, gamma rays. Those types of radiation can separate electrons from atoms, creating ions. [Ham Radio License Manual, page 9-5]
  26. T0C02 Which of the following frequencies has the lowest Maximum Permissible Exposure limit?
    A. 3.5 MHz
    B. 50 MHz
    C. 440 MHz
    D. 1296 MHz
    • B. 50 MHz
    • Frequencies at which the body has the highest SAR are from 30 to 1500 MHz. These are the regions on the MPE graph in Figure T0-2 where the limits for exposure are the lowest. For example, when comparing MPE for amateur bands at 3.5, 50, 440 and 1296 MHz, you can see that MPE is lowest at 50 MHz and highest at 3.5 MHz. [Ham Radio License Manual, page 9-6]
  27. T0C03 What is the maximum power level that an amateur radio station may use at VHF frequencies before an RF exposure evaluation is required?
    A. 1500 watts PEP transmitter output
    B. 1 watt forward power
    C. 50 watts PEP at the antenna
    D. 50 watts PEP reflected power
    • C. 50 watts PEP at the antenna
    • [97.13(c)(1)] — At power levels below 50 watts, the FCC has determined that there is little risk to people. Stations operating with less than 50 watts above 30 MHz are categorically excluded from having to perform a station evaluation. [Ham Radio License Manual, page 9-9]
  28. T0C04 What factors affect the RF exposure of people near an amateur station antenna?
    A. Frequency and power level of the RF field
    B. Distance from the antenna to a person
    C. Radiation pattern of the antenna
    D. All of these choices are correct
    • D. All of these choices are correct
    • The human body absorbs less RF energy at some frequencies and more at others. If you decrease your transmitter output power, you decrease the RF energy radiated from your antenna. Placing antennas farther from people reduces the power density to which they are exposed. Finally, the radiation pattern of the antenna affects where RF exposure will be greatest. [Ham Radio License Manual, page 9-9]
  29. T0C05 Why do exposure limits vary with frequency?
    A. Lower frequency RF fields have more energy than higher frequency fields
    B. Lower frequency RF fields do not penetrate the human body
    C. Higher frequency RF fields are transient in nature
    D. The human body absorbs more RF energy at some frequencies than at others
    • D. The human body absorbs more RF energy at some frequencies than at others
    • At frequencies near the body’s natural resonant frequency, RF energy is absorbed more efficiently and maximum heating occurs. In adults, this frequency usually is about 35 MHz if the person is grounded, and about 70 MHz if the person’s body is insulated from the ground. Also, body parts may be resonant as well; the adult head, for example is resonant around 400 MHz. Body size thus determines the frequency at which most RF energy is absorbed. As the frequency is increased above resonance, less RF heating generally occurs. [Ham Radio License Manual, page 9-6]
  30. T0C06 Which of the following is an acceptable method to determine that your station complies with FCC RF exposure regulations?
    A. By calculation based on FCC OET Bulletin 65
    B. By calculation based on computer modeling
    C. By measurement of field strength using calibrated equipment
    D. All of these choices are correct
    • D. All of these choices are correct
    • [97.13(c)(1)] — You may use a variety of methods to determine that your station complies with FCC RF-exposure regulations. All of the choices given above are correct and valid methods of making that determination. [Ham Radio License Manual, page 9-9]
  31. T0C07 What could happen if a person accidentally touched your antenna while you were transmitting?
    A. Touching the antenna could cause television interference
    B. They might receive a painful RF burn
    C. They might develop radiation poisoning
    D. All of these choices are correct
    • B. They might receive a painful RF burn
    • An RF burn is caused by localized heating of the body at the point of contact with the antenna. While painful, it is rarely serious. This is a good reason why you should install your antenna where people cannot accidentally come in contact with it. [Ham Radio License Manual, page 9-6]
  32. T0C08 Which of the following actions might amateur operators take to prevent exposure to RF radiation in excess of FCC-supplied limits?
    A. Relocate antennas
    B. Relocate the transmitter
    C. Increase the duty cycle
    D. All of these choices are correct
    • A. Relocate antennas
    • Anything you can do to reduce power density in an area of concern will reduce RF exposure. This includes relocating your antennas farther from the area, changing the antenna’s radiation pattern, and reducing power. The exposure limits also change with frequency, so changing frequency to operate on a band with a higher safe exposure limit is also acceptable. [Ham Radio License Manual, page 9-10]
  33. T0C09 How can you make sure your station stays in compliance with RF safety regulations?
    A. By informing the FCC of any changes made in your station
    B. By re-evaluating the station whenever an item of equipment is changed
    C. By making sure your antennas have low SWR
    D. All of these choices are correct
    • B. By re-evaluating the station whenever an item of equipment is changed
    • Whenever you make a change to something that affects power density around your antennas, you should re-evaluate the station. For example, adding an amplifier or changing to an antenna that has more gain will increase power density and you should re-evaluate. If your station is already in compliance and you take a step that decreases RF exposure, such as raising your antennas farther from areas where people are, you don’t need to re-evaluate. [Ham Radio License Manual, page 9-9]
  34. T0C10 Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?
    A. It affects the average exposure of people to radiation
    B. It affects the peak exposure of people to radiation
    C. It takes into account the antenna feedline loss
    D. It takes into account the thermal effects of the final amplifier
    • A. It affects the average exposure of people to radiation
    • Because the effect of RF exposure is heating, average exposure is what is important. Average exposure during any given period depends on how long the transmitter is operating — which is measured by duty cycle. An emission with a lower duty cycle produces less RF exposure for the same PEP output. Duty cycle is the ratio of the transmitted signal’s on-air time to total operating time during the measurement period and has a maximum of 100%. (Duty factor is the same as duty cycle expressed as a fraction, instead of percent, such as 0.25 instead of 25%.) [Ham Radio License Manual, page 9-8]
  35. T0C11 What is meant by “duty cycle” when referring to RF exposure?
    A. The difference between lowest usable output and maximum rated output power of a transmitter
    B. The difference between PEP and average power of an SSB signal
    C. The ratio of on-air time to total operating time of a transmitted signal
    D. The amount of time the operator spends transmitting
    • C. The ratio of on-air time to total operating time of a transmitted signal
    • Because the effect of RF exposure is heating, average exposure is what is important. Average exposure during any given period depends on how long the transmitter is operating — which is measured by duty cycle. An emission with a lower duty cycle produces less RF exposure for the same PEP output. Duty cycle is the ratio of the transmitted signal’s on-air time to total operating time during the measurement period and has a maximum of 100%. (Duty factor is the same as duty cycle expressed as a fraction, instead of percent, such as 0.25 instead of 25%.) [Ham Radio License Manual, page 9-8]

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