Chapter 9: Safety Flashcards
What conductor provides the lowest impedance to RF signals?
Flat Strap
What is a common cure for distorted audio caused by RF current on the shield of a microphone cable?
Ferrite choke
What would cause a broadcast AM or FM radio to receive an amateur radio transmission unintentionally?
The receiver is unable to reject strong signals outside the AM or FM band.
What are common causes of radio frequency interference?
- Fundamental overload
- Harmonics
- Spurious emissions
What is a method to reduce or eliminate interference from an amateur transmitter to a nearby telephone?
Put an RF filter on the telephone
How can overload of a non-amateur radio or TV receiver by an amateur signal be reduced or eliminated?
Block the amateur signal with a filter at the antenna input of the affected receiver.
What actions should you take if a neighbor tells you that your station’s transmissions are interfering with their radio or TV reception?
Make sure that your station is functioning properly and that it does not cause interference to your own radio or television when it is tuned to the same channel.
What can reduce overload to a VHF transceiver from a nearby FM broadcast station?
Band-reject filter
What should you do if something in a neighbor’s home is causing harmful interference to your amateur station?
- Work with your neighbor to identify the offending device
- Politely inform your neighbor about the rules that prohibit the use of devices that cause interference
- Check your station and make sure it meets the standards of good amateur practice
What is a Part 15 device?
An unlicensed device that may emit low-powered radio signals on frequencies used by a licensed service
What is a symptom of RF feedback in a transmitter or transceiver?
Reports of garbled, distorted, or unintelligible voice transmissions
What should be the first step to resolve cable TV interference from your ham radio transmission?
Be sure all TV coaxial connectors are installed properly.
What is a safety hazard of a 12-volt storage battery?
Shorting the terminals can cause burns, fire, or an explosion
What health hazard is presented by electrical current flowing through the body?
It may cause:
- Injury by heating tissue
- Disrupt the electrical functions of cells
- 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 a good way to guard against electrical shock at your station?
- Use three-wire cords and plugs for all AC powered equipment
- Connect all AC powered station equipment to a common safety ground
- Use a circuit protected by ground-fault interrupter
What is a precaution that 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?
Bond them together with heavy wire or conductive strap
What kind of hazard might exist in a power supply when it 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
What 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
What is an important safety rule to remember when using a crank-up tower?
This type of tower must never 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
What is a consideration for installing grounding conductors used for lightning protection?
Sharp bends should be avoided
What establishes grounding requirements for an amateur radio tower or antenna?
Local electrical codes
What is a 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
What frequency has the lowest value for Maximum Permissible Exposure (MPE) 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
- Radiation pattern of the antenna
Why do exposure limits vary with frequency?
The human body absorbs more RF energy at some frequencies than others.
What is an acceptable method to determine that your station complies with FCC RF exposure regulations?
By:
- Calculation based on FCC OET Bulletin 65
- Calculation based on computer modeling
- 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
What action 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 a 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 average 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
