In this episode, i joined Martin Butler M1MRB, Caryn Eve Murray KD2GUT and Ed Durrant DD5LP to discuss the following:
Other news includes:
This episode’s feature is MFJ8504 Review and Understanding HF Controls.
In this episode, i joined Martin Butler M1MRB, Caryn Eve Murray KD2GUT and Ed Durrant DD5LP to discuss the following:
Other news includes:
This episode’s feature is MFJ8504 Review and Understanding HF Controls.
On Tuesday, April 27, Dan, W1DAN, ARRL Eastern Massachusetts Section Technical Coordinator, gave a Zoom presentation on the latest FCC regulations on RF exposure evaluation. These are spelled out in FCC-1926A1, “Proposed Changes in the Commission’s Rules Regarding Human Exposure to Radiofrequency Electromagnetic Fields; Reassessment of Federal Communications Commission Radiofrequency Exposure Limits and Policies.” The document is as long as the title might suggest—159 pages—but W1DAN boiled it down, focusing on what these changes mean for radio amateurs.
A recording of the presentation can be viewed by going to https://drive.google.com/drive/folders/1_qIGZhHyMrha-axJt87Dcu0UZuJO0t8F.
After explaining how RF exposure can be harmful, Dan explained how the rules are changing: The biggest change, he notes, is that amateur radio’s categorical exclusion has been eliminated. What this means is that now every radio amateur will have to perform an RF exposure evaluation of their stations. This now includes mobile and portable stations, including HTs, SOTA/POTA stations, and Field Day and special event stations.
He noted that you must be able to prove that your station is safe. This includes not only performing the evaluation, but also documenting these evaluations, should this data be requested by FCC personnel.
One thing that’s not changing are the maximum permissible exposure (MPE) limits. These are spelled out in FCC OET Bulletin 65, “Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields.” The FCC published this document in August 1997, but it’s still the Bible when it comes to RF exposure. If you don’t have a copy, or have never taken a look at it, you really should do so.
Be careful, though, when reading it. It contains a table (Table 1 on p. 21) that contains a list of output powers at various frequencies. If your station exceeded those limits, then you were required to perform an RF evaluation. Now, however, all amateurs (and other radio services, for that matter) must perform RF exposure evaluations if their output power exceeds 1 mW. We are no longer categorically excluded from performing these evaluations.
OET Bulletin 65 goes on to give guidance on how to calculate or measure exposure levels. Explaining how to do this is outside the scope of this article, but again, you’ll want to refer to the bulletin for more information.
Besides the elimination of the categorical exclusion for amateur radio stations, what else is new is the dates on which amateur radio stations must perform evaluations. They are:
Having said all that, the ARRL’s RF Exposure page has a lot of resources to help you understand this topic and perform your own RF exposure evaluations:
The page also has links to FCC web pages with information on RF exposure.
I’m sure we’ll all be hearing more about this in the days ahead. Hopefully, someone will come out with a simple way to do the modeling or make the calculations. As always, play safe.
QST de W1AW
ARRL Bulletin 11 ARLB011
From ARRL Headquarters
Newington CT April 13, 2021
To all radio amateurs
SB QST ARL ARLB011
The FCC has announced that rule changes detailed in a lengthy 2019 Report and Order governing RF exposure standards go into effect on May 3, 2021. The new rules do not change existing RF exposure (RFE) limits but do require that stations in all services, including amateur radio, be evaluated against existing limits, unless they are exempted. For stations already in place, that evaluation must be completed by May 3, 2023. After May 3 of this year, any new station, or any existing station modified in a way that’s likely to change its RFE profile – such as different antenna or placement or greater power – will need to conduct an evaluation by the date of activation or change.
The Report and Order can be found online in PDF format.
“In the RF Report and Order, the Commission anticipated that few parties would have to conduct reevaluations under the new rules and that such evaluations will be relatively straightforward,” the FCC said in an April 2 Public Notice. “It nevertheless adopted a 2-year period for parties to verify and ensure compliance under the new rules.”
The Amateur Service is no longer categorically excluded from certain aspects of the rules, as amended, and licensees can no longer avoid performing an exposure assessment simply because they are transmitting below a given power level.
“For most amateurs, the major difference is the removal of the categorical exclusion for amateur radio, which means that ham station owners must determine if they either qualify for an exemption or must perform a routine environmental evaluation,” said Greg Lapin, N9GL, chair of the ARRL RF Safety Committee and a member of the FCC Technological Advisory Council (TAC).
“Ham stations previously excluded from performing environmental evaluations will have until May 3, 2023, to perform these. After May 3, 2021, any new stations or those modified in a way that affects RF exposure must comply before being put into service,” Lapin said.
The December 2019 RF Report and Order changes the methods that many radio services use to determine and achieve compliance with FCC limits on human exposure to RF electromagnetic fields. The FCC also modified the process for determining whether a particular device or deployment is exempt from a more thorough analysis by replacing a service-specific list of transmitters, facilities, and operations for which evaluation is required with new streamlined formula-based criteria. The R&O also addressed how to perform evaluations where the exemption does not apply, and how to mitigate exposure.
Amateur radio licensees will have to determine whether any existing facilities previously excluded under the old rules now qualify for an exemption under the new rules. Most will, but some may not.
“For amateurs, the major difference is the removal of the categorical exclusion,” Lapin said, “which means that every ham will be required to perform some sort of calculation, either to determine if they qualify for an exemption or must perform a full-fledged exposure assessment. For hams who previously performed exposure assessments on their stations, there is nothing more to do.”
The ARRL Laboratory staff is available to help amateurs to make these determinations and, if needed, perform the necessary calculations to ensure their stations comply. ARRL Laboratory Manager Ed Hare, W1RFI, who helped prepare ARRL’s RF Exposure and You book, explained it this way. “The FCC did not change any of the underlying rules applicable to amateur station evaluations,” he said. “The sections of the book on how to perform routine station evaluations are still valid and usable, especially the many charts of common antennas at different heights.” Hare said ARRL Lab staff also would be available to help amateurs understand the rules and evaluate their stations.”
RF Exposure and You is available in PDF format for free download. The chapter on RF safety from the ARRL Handbook is also available online. The ARRL website also has an RF Safety page.
The ARRL RF Safety Committee is working with the FCC to update the FCC’s aids for following human exposure rules – OET Bulletin 65 and OET Bulletin 65 Supplement B for Radio Amateurs. In addition, ARRL is developing tools that all hams can use to perform exposure assessments.
NNNN
/EX
For this episode, I joined Martin M1MRB, Leslie Butterfield G0CIB, and Edmund Spicer M0MNG. We discussed the following:
The first item was the most interesting. Ofcom, which is the U.K. equivalent of the FCC, will be requiring anyone operating a transmitter at more than 10 W EIRP to perform an evaluation that will ensure their equipment continues to operate within international electromagnetic field (EMF) guidelines. This includes keeping data and records of any testing to demonstrate their compliance.
This has, of course, raised the hackles of many U.K. hams, as well as boat owners, but Leslie, G0CIB, thinks that it’s better to get on board than to get all worked up about it. I seem to recall something similar being proposed here, and if I had to hazard a guess, we’ll have some similar regulation here before long.
There will be a simple way to make this evaluation. They plan to publish a spreadsheet that will allow you to plug in an operating frequency and transmitter output power and get back a safe operating distance. I played with the trial version for a bit, and it certainly seemed easy enough to use. Remember that it’s all about being safe.
If you learn nothing else from this manual, I hope that you learn to be safe when setting up your station, building antennas, or operating a radio. It’s unfortunate, but hams every year lose their lives in accidents that could have been prevented. In this chapter, we will cover RF safety and electrical safety.
By RF safety, we mean staying below the limits for exposure to the RF energy generated by amateur radio transmitters. These limits are set by the FCC and are called maximum permissible exposure, or MPE.
To determine the amount of RF that you’ve been exposed to you have to take into account the time you’re exposed to the RF radiation, the level of the RF radiation, and the duty cycle of the radiation. One way that RF energy can affect human body tissue is that it heats body tissue.
QUESTION: What is one way that RF energy can affect human body tissue? (G0A01)
ANSWER: It heats body tissue
QUESTION: What does “time averaging” mean in reference to RF radiation exposure? (G0A04)
ANSWER: The total RF exposure averaged over a certain time
QUESTION: What effect does transmitter duty cycle have when evaluating RF exposure? (G0A07)
ANSWER: A lower transmitter duty cycle permits greater short-term exposure levels
QUESTION: Which of the following properties is important in estimating whether an RF signal exceeds the maximum permissible exposure (MPE)? (G0A02)
ANSWER: All of these choices are correct
• Its duty cycle
• Its frequency
• Its power density
It’s important to keep in mind the MPE limits when installing an antenna, especially an indoor transmitting antenna because the closer you, and other people living with you, are to the antenna, the higher the exposure will be.
QUESTION: What precaution should you take if you install an indoor transmitting antenna? (G0A11)
ANSWER: Make sure that MPE limits are not exceeded in occupied areas
To ensure compliance with RF safety regulations when transmitter power exceeds levels specified in part 97.13, you must routinely perform RF exposure evaluations. You can do this by using the evaluation procedure found in FCC OET Bulletin 65 or by computer modeling of your station setup. In some cases, you may actually want to make field strength measurements with a calibrated instrument to ensure your safety.
QUESTION: Which of the following steps must an amateur operator take to ensure compliance with RF safety regulations when transmitter power exceeds levels specified in FCC Part 97.13? (G0A08)
ANSWER: Perform a routine RF exposure evaluation
QUESTION: How can you determine that your station complies with FCC RF exposure regulations? (G0A03)
ANSWER: All of these choices are correct
• By calculation based on FCC OET Bulletin 65
• By calculation based on computer modeling
• By measurement of field strength using calibrated equipment
QUESTION: What type of instrument can be used to accurately measure an RF field? (G0A09)
ANSWER: A calibrated field strength meter with a calibrated antenna
If an evaluation of your station shows RF energy radiated from your station exceeds permissible limits, then you must take action. This might mean reducing your transmitter power or moving antennas. If you use a directional antenna, you should ensure that it cannot be pointed in a direction that would cause people to receive more than the maximum permissible exposure.
QUESTION: What must you do if an evaluation of your station shows RF energy radiated from your station exceeds permissible limits? (G0A05)
ANSWER: Take action to prevent human exposure to the excessive RF fields
QUESTION: What is one thing that can be done if evaluation shows that a neighbor might receive more than the allowable limit of RF exposure from the main lobe of a directional antenna? (G0A10)
ANSWER: Take precautions to ensure that the antenna cannot be pointed in their direction
In addition to ensuring that you’re not exposed to high-energy RF fields, there are some simple precautions that you should take when installing an antenna. The first thing you should do is to turn off the transmitter and disconnect the feedline. Also, if you are installing a ground-mounted antenna, make sure that no one can touch it while you’re transmitting, as doing so may cause RF burns.
QUESTION: What precaution should you take whenever you adjust or repair an antenna? (G0B14)
ANSWER: Turn off the transmitter and disconnect the feed line
QUESTION: What precaution should be taken when installing a ground-mounted antenna? (G0A06)
ANSWER: It should be installed such that it is protected against unauthorized access
Following safe work practices when installing or working on an antenna tower is paramount. Always make sure that anyone climbing the tower is using the appropriate safety belt or harness and that no power can be supplied to any circuits powering devices on the tower.
QUESTION: Which of these choices should be observed when climbing a tower using a safety belt or harness? (G0B07)
ANSWER: Confirm that the belt is rated for the weight of the climber and that it is within its allowable service life
QUESTION: What should be done by any person preparing to climb a tower that supports electrically powered devices? (G0B08)
ANSWER: Make sure all circuits that supply power to the tower are locked out and tagged
Properly grounding a tower is also an important safety practice. Never solder wires that connect a tower to ground, as they will simply be destroyed by a lightning strike. Instead, makes sure that the legs of the tower are properly grounded by bonding them together and then bonding them to the tower’s ground rods.
QUESTION: Why should soldered joints not be used with the wires that connect the base of a tower to a system of ground rods? (G4C07)
ANSWER: A soldered joint will likely be destroyed by the heat of a lightning strike
QUESTION: Which of the following is good practice for lightning protection grounds? (G0B11)
ANSWER: They must be bonded together with all other grounds
When wiring your station or “shack,” pay special attention to the currents that the circuit must supply and use the appropriate wire sizes and fuse sizes. These values are specified by the National Electrical Code (NEC). You should refer to the NEC for any question you might have about electrical safety.
QUESTION: Which of the following is covered by the National Electrical Code? (G0B06)
ANSWER: Electrical safety inside the ham shack
QUESTION: According the National Electrical Code, what is the minimum wire size that may be used safely for wiring with a 20 ampere circuit breaker? (G0B02)
ANSWER: AWG number 12
QUESTION: Which size of fuse or circuit breaker would be appropriate to use with a circuit that uses AWG number 14 wiring? (G0B03)
ANSWER: 15 amperes
For some devices, such as a linear amplifier, you may have to install a 240 VAC circuit. Again, the National Electrical Code calls out requirements for wiring this kind of circuit. As with 120 VAC circuits, it’s a good idea to use ground fault circuit interrupters (GFCIs) to detect ground faults and prevent unsafe situations from occurring.
QUESTION: Which wire or wires in a four-conductor connection should be attached to fuses or circuit breakers in a device operated from a 240 VAC single phase source? (G0B01)
ANSWER: Only the two wires carrying voltage
QUESTION: Which of the following conditions will cause a Ground Fault Circuit Interrupter (GFCI) to disconnect the 120 or 240 Volt AC line power to a device? (G0B05)
ANSWER: Current flowing from one or more of the voltage-carrying wires directly to ground
Some equipment may have features that make it safer to use or maintain. For example, some power supplies have interlock switches. These switches disconnect the power supply when an enclosure is opened.
QUESTION: What is the purpose of a power supply interlock? (G0B12)
ANSWER: To ensure that dangerous voltages are removed if the cabinet is opened.
In an emergency, you may want to power your station with batteries or an emergency power generator. Again, please do so safely. Always make sure that before turning on a generator, the incoming utility power feed is disconnected, and if you’re using a gasoline-powered generator, operate it in a well-ventilated space away from people.
QUESTION: What must you do when powering your house from an emergency generator? (G0B13)
ANSWER: Disconnect the incoming utility power feed
QUESTION: Which of the following is true of an emergency generator installation? (G0B09)
ANSWER: The generator should be located in a well-ventilated area
QUESTION: Which of the following is a primary reason for not placing a gasoline-fueled generator inside an occupied area? (G0B04)
ANSWER: Danger of carbon monoxide poisoning
Finally, consider that the lead in the solder commonly used in amateur radio equipment might constitute a hazard. Remember what your mother always told you to do before dinner? After using lead-tin solder, wash your hands!
QUESTION: Which of the following is a danger from lead-tin solder? (G0B10)
ANSWER: Lead can contaminate food if hands are not washed carefully after handling
A letter in the December 2017 QST caught my eye. It had a safety tip for dealing with high voltage circuits, and I thought I would pass it along. It’s reprinted with permission from the author, Joseph Birsa, N3TTE…..Dan
Reading the article on DMM’s in the October 2017 issue of QST reminded me of a safety practice I want to pass along. Always, always, ALWAYS check the meter leads using the resistance function of a meter BEFORE checking a hazardous voltage! (Or any voltage or current for that matter.)
To do this, BEFORE YOU DO ANYTHING ELSE, turn the meter to ohms and short the tips of the leads to verify continuity (zero or low reading). Then, switch the meter to the appropriate function and proceed.
When I was starting out as an electrical engineer, a field engineer, who was a ham by the way, told me a story about an electrician who opened an equipment cabinet powered by three-phase, 480 V. Before beginning, he used his meter to check the 480 V. Seeing no voltage, he proceeded and was subsequently electrocuted! When they checked his meter, they found one of the leads was opened. Or perhaps a fuse was blown.
Since then, the first thing I do when I start to use a meter is to use the resistance function to check lead continuity.
Since sections G0A and G0B are relatively short, I’m lumping them into one blog post. There were only a few minor changes to these questions.
If you learn nothing else from this manual, I hope that you learn to be safe when setting up your station, building antennas, or operating a radio. It’s unfortunate, but hams every year lose their lives in accidents that could have been prevented. In this chapter, we will cover RF safety and electrical safety.
By RF safety, we mean safe exposure to the RF energy generated by amateur radio transmitters. One way that RF energy can affect human body tissue is that it heats body tissue. (G0A01) In reference to RF radiation exposure, “time averaging” means the total RF exposure averaged over a certain time. (G0A04)When evaluating RF exposure, a lower transmitter duty cycle permits greater short-term exposure levels. (G0A07)
All of these choices are correct when talking about properties that are important in estimating whether an RF signal exceeds the maximum permissible exposure (MPE) (G0A02):
If you install an indoor transmitting antenna, make sure that MPE limits are not exceeded in occupied areas. (G0A11)
How do you know if you’re being exposed to higher levels of RF radiation than you should be? One way is to measure the RF field. A calibrated field-strength meter with a calibrated antenna can be used to accurately measure an RF field. (G0A09)
To ensure compliance with RF safety regulations when transmitter power exceeds levels specified in part 97.13, an amateur operator must perform a routine RF exposure evaluation. (G0A08) All of these choices are correct for ways that you can use to determine that your station complies with FCC RF exposure regulations (G0A03):
If an evaluation of your station shows RF energy radiated from your station exceeds permissible limits, you should take action to prevent human exposure to the excessive RF fields. (G0A05) If an evaluation shows that a neighbor might receive more than the allowable limit of RF exposure from the main lobe of a directional antenna, take precautions to ensure that the antenna cannot be pointed in their direction. (G0A10)
In addition to ensuring that you’re not exposed to high-energy RF fields, there are some simple precautions that you should take when installing and tuning an antenna. Turn off the transmitter and disconnect the feed line whenever you make adjustments or repairs to an antenna. (G0A12) When installing a ground-mounted antenna, it should be installed such that it is protected against unauthorized access. (G0A06)
Following safe work practices when installing or working on an antenna tower is paramount. When climbing on a tower using a safety belt or harness is to confirm that the belt is rated for the weight of the climber and that it is within its allowable service life. (G0B07)
Any person preparing to climb a tower that supports electrically powered devices should make sure all circuits that supply power to the tower are locked out and tagged. (G0B08) Soldered joints should not be used with the wires that connect the base of a tower to a system of ground rods because a soldered joint will likely be destroyed by the heat of a lightning strike. (G0B09) A good practice for lightning protection grounds is that they must be bonded together with all other grounds. (G0B11)
When wiring a “shack,” pay special attention to the currents that the circuit must supply and use the appropriate wire sizes and fuse sizes. Electrical safety inside the ham shack is covered by the National Electrical Code. (G0B14)
According to the code, AWG number 12 is the minimum wire size that may be safely used for a circuit that draws up to 20 amperes of continuous current. (G0B02) 15 amperes is the size of fuse or circuit breaker that would be appropriate to use with a circuit that uses AWG number 14 wiring. (G0B03)
For some devices, such as a linear amplifier, you may have to install a 240 VAC circuit. When doing so, remember only the two wires carrying voltage in a four-conductor connection should be attached to fuses or circuit breakers in a device operated from a 240-VAC single-phase source. (G0B01) Current flowing from one or more of the voltage-carrying wires directly to ground will cause a Ground Fault Circuit Interrupter (GFCI) to disconnect the 120 or 240 Volt AC line power to a device. (G0B05)
Another way to make the shack safer, is to properly ground your equipment. The metal enclosure of every item of station equipment must be grounded because it ensures that hazardous voltages cannot appear on the chassis. (G0B06)
Some equipment may have features that make it safer to use or maintain. For example, some power supplies have interlock switches. The purpose of a transmitter power supply interlock is to ensure that dangerous voltages are removed if the cabinet is opened. (G0B12)
Finally, consider that the lead in the solder commonly used in amateur radio equipment might constitute a hazard. One danger from lead-tin solder is that lead can contaminate food if hands are not washed carefully after handling. (G0B10)
In an emergency, you may want to power your station with batteries or an emergency power generator. Again, please do so safely. When powering your house from an emergency generator, you must disconnect the incoming utility power feed. (G0B13)
Gasoline-powered generators may emit exhaust gases that could be hazardous. For an emergency generator installation, the generator should be located in a well ventilated area. (G0B15) Danger of carbon monoxide poisoning is a primary reason for not placing a gasoline-fueled generator inside an occupied area. (G0B04)
In this section, the answer to T0C11 was changed, and T0C12 and T0C13 were added. All good additions, in my opinion…Dan
Finally, let’s consider the safety hazards of being exposed to radio waves. When using high power, you are required to perform an RF exposure evaluation, even though VHF and UHF radio signals are non-ionizing radiation. (T0C01) RF radiation differs from ionizing radiation (radioactivity) in that RF radiation does not have sufficient energy to cause genetic damage. (T0C12)
Even so small levels of RF energy can be unsafe. The maximum power level that an amateur radio station may use at VHF frequencies before an RF exposure evaluation is required is 50 watts PEP at the antenna. (T0C03)
How do you perform an RF exposure evaluation? All of these choices are correct as acceptable methods to determine if your station complies with FCC RF exposure regulations (T0C06):
One of the factors to consider when performing an RF exposure evaluation is the duty cycle of your transmissions. The term “duty cycle” when referring to RF exposure is the percentage of time that a transmitter is transmitting. (T0C11) 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. (T0C10) A transmission with a lower duty cycle would be less hazardous than a high duty cycle transmission.
Consider this example: 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. (T0C13)
Because of the way radio waves interact with the body, the exposure limits are different for each amateur radio band. Exposure limits vary with frequency because the human body absorbs more RF energy at some frequencies than at others. (T0C05) The 50 MHz band has the lowest Maximum Permissible Exposure limit. (T0C02) All of these choices are correct when talking about factors that affect the RF exposure of people near an amateur station antenna (T0C04):
So, what should you do if your RF exposure evaluation shows that people are being exposed to excessive RF? One action amateur operators might take to prevent exposure to RF radiation in excess of FCC-supplied limits is to relocate antennas. (T0C08) You could also lower the power or simply transmit less.
After the initial RF exposure evaluation, you make sure your station stays in compliance with RF safety regulations by re-evaluating the station whenever an item of equipment is changed. (T0C09)
There were no changes to this section that I could find…Dan
Antenna safety is also of primary concern. There are two aspects of antenna safety—being safe when installing an antenna and safely operating an antenna.
When putting up an antenna tower, an important safety precaution is to look for and stay clear of any overhead electrical wires. (T0B04) When installing an antenna, make sure that it is far enough from power lines, so that if the antenna falls unexpectedly, no part of it can come closer than 10 feet to the power wires. (T0B06) This is the reason you should avoid attaching an antenna to a utility pole. The antenna could contact high-voltage power wires. (T0B09)
You also should position the antenna so that no one can touch it while you are transmitting. If a person accidentally touched your antenna while you were transmitting, they might receive a painful RF burn. (T0C07)
Another safety tip is to use a gin pole designed for use with the tower that you’re installing. The purpose of a gin pole is to lift tower sections or antennas. (T0B05)
At all times when any work is being done on the tower, members of a tower work team should wear a hard hat and safety glasses. (T0B01) Before climbing an antenna tower, it is a good precaution to put on a climbing harness and safety glasses. (T0B02) It is never safe to climb a tower without a helper or observer. (T0B03) When using a crank-up tower, an important safety rule to remember is that this type of tower must never be climbed unless it is in the fully retracted position. (T0B07)
Grounding is very important when installing a tower because the tower is basically a big lightning rod. Local electrical codes establish grounding requirements for an amateur radio tower or antenna. (T0B11)
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. (T0B08) When installing ground wires on a tower for lightning protection, it is good practice to ensure that connections are short and direct. (T0B12) Sharp bends must be avoided when installing grounding conductors used for lightning protection. (T0B10)
Lightning can also be conducted down a feedline and into your shack. To prevent this, several manufacturers make devices designed to shunt this current to ground before it gets into the shack. When installing devices for lightning protection in a coaxial cable feedline, ground all of the protectors to a common plate which is in turn connected to an external ground. (T0A07)
Several changes were made to this section that I don’t like. For example, the question pool committee removed the question about 30V being the commonly accepted value for the lowest voltage that can cause a dangerous electric shock. The question about 100 mA being the lowest amount of electrical current flowing through the body that is likely to cause death was removed from the 2010 question pool, so now there are no questions at all about these values. I’m leaving them in the study guide, though, because I think they’re important.
The committee also removed the question about charging a 12 V battery by connecting it to your car battery and running the engine. I’m all for removing that question. It was replaced by a question about what might happen if you short the terminals of a 12V battery…Dan
BE SAFE!
When operating or working on amateur radio equipment, it’s possible to come into contact with dangerous voltages and currents. Because it would be a shame to lose a single person, it’s important to know how to be safe when working with electricity. Having said that, 30 volts is the commonly accepted value for the lowest voltage that can cause a dangerous electric shock, and 100 mA is the lowest amount of electrical current flowing through the body that is likely to cause death. These are not very large values.
All of these choices are correct when considering how current flowing through the body can cause a health hazard (T0A02):
Three-wire electrical outlets and plugs are safer than two-wire outlets and plugs, and you should use three-wire plugs for all of your amateur radio equipment. The third wire provides an independent, or safety ground. Safety ground is connected to the green wire in a three- wire electrical AC plug. (T0A03)
All of these choices are correct when choosing a good way to guard against electrical shock at your station (T0A06):
Individual pieces of equipment may have their own fuses to protect that piece of equipment should something happen that causes that equipment to draw excessive current. The purpose of a fuse in an electrical circuit is to interrupt power in case of overload. (T0A04) When replacing a fuse, always replace the blown fuse with a fuse of the same type and value. It is, for example, unwise to install a 20-ampere fuse in the place of a 5-ampere fuse because excessive current could cause a fire. (T0A05)
If you plan to build your own equipment, be sure to include fuses in your designs. 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. (T0A08)
Whenever you’re working on equipment, be sure to disconnect it from the power lines, and even then be careful working around a power supply’s capacitors. If a power supply is turned off and disconnected, you might receive an electric shock from stored charge in large capacitors. (T0A11)
Finally, it’s necessary to take precautions when using batteries to power your amateur radio station. Conventional 12-volt storage batteries present several safety hazards. Shorting the terminals can cause burns, fire, or an explosion (T0A01), explosive gas can collect if not properly vented (T0A09), and, if a lead-acid storage battery is charged or discharged too quickly, the battery could overheat and give off flammable gas or explode. (T0A10)