T10
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Subelement T0
Electrical Safety, power circuits, antenna installation and RF hazards.
Shorting the terminals of a 12-volt storage battery is a safety hazard and can cause burns, fire, or an explosion. A lead-acid storage battery could overheat and give off flammable gas or explode if charged or discharged too quickly. The hazard presented by a conventional 12-volt storage battery is explosive gas can collect if not properly vented.
Current flowing through the body can cause a health hazard by heating tissue, disrupts the electrical functions of cells or causes involuntary muscle contractions. Exposure limits vary because the human body absorbs more RF energy at some frequencies than at others. 50 watts PEP at the antenna is the maximum power level that an amateur radio station may use at VHF frequencies before an RF exposure evaluation is required. 50 MHz has the lowest value for Maximum Permissible Exposure limit. Frequency and power level of the RF field, distance from the antenna to a person and radiation pattern of the antenna affect the RF exposure of people near an amateur station antenna. By re-evaluating the station whenever an item of equipment is changed you can make sure your station stays in compliance with RF safety regulations. Duty cycle is one of the factors used to determine safe RF radiation exposure levels because It affects the average exposure of people to radiation. The percentage of time that a transmitter is transmitting is the definition of duty cycle during the averaging time for RF exposure. If the averaging time for exposure is 6 minutes, 2 times as much power density is permitted if the signal is present for 3 minutes and absent for 3 minutes rather than being present for the entire 6 minutes. Relocate antennas to prevent exposure to RF radiation in excess of FCC-supplied limits. VHF and UHF radio signals are non-ionizing radiation. RF radiation differs from ionizing radiation (radioactivity) because RF radiation does not have sufficient energy to cause genetic damage.
A good way to guard against electrical shock at your station is to use three-wire cords and plugs for all AC powered equipment, connect all AC powered station equipment to a common safety ground and use a circuit protected by a ground-fault interrupter. Safety ground is connected to the green wire in a three-wire electrical AC plug. The purpose of a fuse in an electrical circuit is to interrupt power in case of overload. It is unwise to install a 20-ampere fuse in the place of a 5-ampere fuse because excessive current could cause a fire. A fuse or circuit breaker in series with the AC hot conductor should always be included in home-built equipment that is powered from 120V AC power circuits.
You might receive an electric shock from the charged stored in large capacitors in a power supply when it is turned off and disconnected. If a person accidentally touched your antenna while you were transmitting they might receive a painful RF burn.
Never climb a tower without a helper or observer. Look for and stay clear of any overhead electrical wires is an important safety precaution to observe when putting up an antenna tower. The minimum safe distance from a power line to allow when installing an antenna is no part of it can come closer than 10 feet to the power wires. Put on a climbing harness and safety glasses is a good precaution to observe before climbing an antenna tower. Members of a tower work team should wear a hard hat and safety glasses at all times when any work is being done on the tower. A safety rule to remember when using a crank-up tower is it must never be climbed unless it is in the fully retracted position. To lift tower sections or antennas is the purpose of a gin pole. Local electrical codes establish grounding requirements for an amateur radio tower or antenna. Separate eight-foot long ground rods for each tower leg, bonded to the tower and each other is considered to be a proper grounding method for a tower. Ensure that connections are short and direct when installing ground wires on a tower for lightning protection. When grounding conductors are used for lightning protection sharp bends must be avoided.
Ground all of the protectors(PL-259) to a common plate, which is in turn connected to an external ground when installing devices for lightning protection for coaxial cable. You should avoid attaching an antenna to a utility pole it could contact high-voltage power wires.
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SUBELEMENT T0
Electrical safety: AC and DC power circuits;
antenna installation; RF hazards
[3 Exam Questions – 3 Groups]
Which of the following is a safety hazard of a 12-volt storage battery?
- Shorting the terminals can cause burns, fire, or an explosion
The health hazard is presented by electrical current flowing through the body It may cause injury by heating tissue, It may disrupt the electrical functions of cells or It may cause involuntary muscle contractions
In the United States, what is connected to the green wire in a three-wire electrical AC plug?
- Equipment ground
What is the purpose of a fuse in an electrical circuit?
- To interrupt power in case of overload
Why is it unwise to install a 20-ampere fuse in the place of a 5-ampere fuse?
- Excessive current could cause a fire
A good way to guard against electrical shock at your station is a use three-wire cords and plugs for all AC powered equipment, connect all AC powered station equipment to a common safety ground and use a circuit protected by a ground-fault interrupter
Which of these precautions should be taken when installing devices for lightning protection in a coaxial cable feed line?
- Mount all of the protectors on a metal plate that is in turn connected to an external ground rod
What safety equipment should always be included in home-built equipment that is powered from 120V AC power circuits?
- A fuse or circuit breaker in series with the AC hot conductor
What should be done to all external ground rods or earth connections?
C. Bond them together with heavy wire or conductive strap
What can happen if a lead-acid storage battery is charged or discharged too quickly?
- The battery could overheat, give off flammable gas, or explode
What kind of hazard might exist in a power supply when it is turned off and disconnected?
- You might receive an electric shock from the charge stored in large capacitors
When should members of a tower work team wear a hard hat and safety glasses?
- At all times when any work is being done on the tower
What is a good precaution to observe before climbing an antenna tower?
- Put on a carefully inspected climbing harness (fall arrester) and safety glasses
Under what circumstances is it safe to climb a tower without a helper or observer?
- Never
Which of the following is an important safety precaution to observe when putting up an antenna tower?
- Look for and stay clear of any overhead electrical wires
What is the purpose of a gin pole?
- To lift tower sections or antennas
What is the minimum safe distance from a power line to allow when installing an antenna?
- Enough so that if the antenna falls unexpectedly, no part of it can come closer than 10 feet to the power wires
Which of the following is an important safety rule to remember when using a crank-up tower?
- This type of tower must not be climbed unless retracted or mechanical safety locking devices have been installed
What is considered to be a proper grounding method for a tower?
- Separate eight-foot long ground rods for each tower leg, bonded to the tower and each other
Why should you avoid attaching an antenna to a utility pole?
- The antenna could contact high-voltage power lines
Which of the following is true when installing grounding conductors used for lightning protection?
- Sharp bends must be avoided
Which of the following establishes grounding requirements for an amateur radio tower or antenna?
- Local electrical codes
Which of the following is good practice when installing ground wires on a tower for lightning protection?
- Ensure that connections are short and direct
What is the purpose of a safety wire through a turnbuckle used to tension guy lines?
- Prevent loosening of the guy line from vibration
What type of radiation are VHF and UHF radio signals?
- Non-ionizing radiation
Which of the following frequencies has the lowest value for Maximum Permissible Exposure limit?
- 50 MHz
What is the maximum power level that an amateur radio station may use at VHF frequencies before an RF exposure evaluation is required?
- 50 watts PEP at the antenna
What factors affect the RF exposure of people near an amateur station antenna?
- Frequency and power level of the RF field, Distance from the antenna to a person and Radiation pattern of the antenna
Why do exposure limits vary with frequency?
- The human body absorbs more RF energy at some frequencies than at others
Which of the following is an acceptable method to determine that your station complies with FCC RF exposure regulations?
By calculation based on FCC OET Bulletin 65, By calculation based on computer modeling or By measurement of field strength using calibrated equipment
What could happen if a person accidentally touched your antenna while you were transmitting?
- They might receive a painful RF burn
Which of the following actions might amateur operators take to prevent exposure to RF radiation in excess of FCC-supplied limits?
- Relocate antennas
How can you make sure your station stays in compliance with RF safety regulations?
- By re-evaluating the station whenever an item of equipment is changed
Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?
- It affects the average exposure of people to radiation
What is the definition of duty cycle during the averaging time for RF exposure?
- The percentage of time that a transmitter is transmitting
How does RF radiation differ from ionizing radiation (radioactivity)?
- RF radiation does not have sufficient energy to cause genetic damage
If the averaging time for exposure is 6 minutes, how much power density is permitted if the signal is present for 3 minutes and absent for 3 minutes rather than being present for the entire 6 minutes?
- 2 times as much
END OF Questions
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