Home - About AR - Learning Material - Exams - Clubs - Posters
While using a hand-held radio is generally a safe activity, some aspects of the hobby can involve hazardous voltages or potentially damaging currents, outdoor antennas can attract lightning strikes, and climbing masts and towers can be risky. This section is on mitigating these hazards.
Voltages below around 30 volts are generally considered safe, but short circuiting batteries and large power supplies can cause large sparks, fires, and other damage.
Fuses contain a thin wire or strip of metal, and if a current above the rated current is drawn through the fuse, the fuse wire will melt, interrupting the flow of current. If there is a heavy short in a high-current circuit the fuse will open in a fraction of a second, and in glass fuses this is indicated by the wire vaporising, and becoming a mirrored metal glazing inside the fuse. When the overload is lower, the fuse can take minutes or hours to operate.
Installing a mobile radio in a car or pick-up truck, etc, typically involves running a pair of heavy conductors from the battery to the cabin through the firewall, often using an existing penetration, being careful to maintain the seal. As close to the battery as possible a fuse, such as an "ATC" or "ATO" standard plastic-bodied automotive fuse. The positive line should be fused, based on the rating of the cable. Some say the negative should be fused, others not, based on the fact that the body of the radio may be grounded, or the shield of the coax may be grounded at the antenna base. One option is to use a higher value fuse than in the positive, such as 40 amps. Near the radio there is the option of fusing again, based on the current draw of the radio, lower than the first positive fuse.
|A backlit image showing a selection of ATC / ATO / ATS automotive fuses, showing different thicknesses of the fuse element. The blades are 5.25 mm wide, with a 4 mm gap.|
The ratings are:
Purple 3 A, Dark Grey 1 A, Orange 40 A, Orange 40 A (ATC);
Red 10 A, pink 4 A, Mauve 35 A, Clear 25 A.
Like 40A, 35A is beyond the standard, and blue-green, the standard for Maxi-fuses, is also used. Other common values are mid-blue, 15 A; and yellow, 20A.
|A glass fuse, rated at 10A, 250 V. It is about 20 mm x 5 mm (or 3/4" X 3/16").|
This is thus physically smaller than many similar fuses.
|Left:A ceramic fuse, rated at 10 Amp, 250 volts AC, but only 125 volts DC. Similar looking fuses are used in multimeters.|
Right:While only rated at 20 amps, the physical size is not related to the carrying current, but the breaking current. High Rupture Current fuses are used in situations where there is the potential of a very large current flowing, should a short occur. If a "reverse vending machine" for drink packaging deposit refunds were to be placed in a car-park next to the 750 kVA transformer for the shopping centre, and a short occurred in the machine, then a huge current could flow, resulting in an explosive release of energy. If the wee glass fuse above were used, the current would arc across the gap. In the HRC fuse the current flow would melt the sand in the fuse, making glass which cuts the current flow. I believe the voltage rating is 440 volts.
In devices such as multimeters, following the manual when replacing fuses is important, as if current bridges the gap in a cheap fuse, you could be seriously injured by an arc-flash.
Fuse symbol: ⏛
When designing equipment selecting fuses is somewhat of an art, and includes considerations such as transformer inrush current, capacitor charging current, and motor start-up current.
You should not replace a low value fuse with one of a higher value, as a fault may allow a current high enough to cause a fire to occur, while not blowing the fuse.
Not on the test, but a "thermal fuse" is a small two-terminal device which goes open circuit when the temperature inside a piece of equipment rises to a dangerous level. As most are not re-settable, they are not soldered in circuit, as this heat would make them open circuit.
Circuit beakers, which sense over-current by magnetic or thermal means, can also be used in the place of a fuse, subject to parameters such as operating speed and breaking current. There are easily reset, and are popular in aircraft.
The following are all rechargeable technologies.
Lead-acid batteries, such as car and marine batteries can generate hydrogen and oxygen gases when charging or being heavily discharged. These are explosive in combination. They can be ignited by spark from a short, or when attaching jumper leads, or removing charger leads without turning off the charger. The voltage per cell is 2.0 to 2.2 volts.
Improperly charging or shorting lithium batteries, as well as puncturing them, can result in "exciting" outcomes, including "vent with flame". Depending on the exact chemistry, cell voltage is 3.6 to 4.3 volts. Various bags are available, which claim to contain this energy. Lithium cells or batteries are used in hand-held radios; and Lithium Polymer (LiPo) packs designed for electric model aircraft can be used to power mobile radios, noting the capacity to supply very high fault currents.
Mythbusters Jr. conducted a series of experiments involving crushing, piercing, and heating various Lithium batteries, which resulted in much fire, toxic smoke, and some (small) explosions. DO NOT throw these batteries in the trash, but take them to a recycling point. Somewhat concerningly, disposable "vape" products use rechargable Lithium cells, which are then discarded in the street, or in municipal garbage collections. While vaping can cause severe lung damage, recovering the cells may be useful, following hygene and safety practices, and recharged. Big Clive on YouTube has several videos on this.
One cause of the reputation damaging incidents is the attempt to have charging times shorter than the competition. Poor cell manufacture or design is also a problem, including in the Samsung Note S7 case, just one of several of their products which is "pyrotechnic". Apple also has its own battery fire and explosion issues.
Nickel-Cadmium batteries include both small "dry" cells, and larger wet cells, the latter used for things such as starting aircraft. With proper care the latter can have a life of something like 100 years in amateur radio service. Even the NiCad (or Ni-Cd) cells used in hand-held radios can deliver high currents. There is also a related Nickel-Metal-Hydride (NiMH) technology, with similar characteristics to NiCad, but with some compromises. Both have a cell voltage of around 1.2 volts, so 10 are needed to power a 12 volt device. MiMH are considered "greener" as they don't contain Cadmium, but may last for fewer charge-discharge cycles.
Beyond the exam, it is possible to crack the ultrasonic weld in some battery packs by using a hammer, and tapping along the seam, or to otherwise open the them, and replace the cells (safety glasses would be a good idea). As the cells may have leaked alkaline fluid, it is a good idea to wear nitrile gloves. In most cases, all should be replaced. Replacement NiCad or NiMH cells are usually quite affordable. These have metal strips spot-welded to the terminals, and these can be soldered to. Soldering directly to cells in a bad idea, as overheating can cause cells to rupture.
A somewhat rarer technology, available in AA (UM-3) and AAA (UM-4) is NiZn, Nickel-Zinc, with a terminal voltage of 1.6 volts, so quite good replacements for standard cells. Some hand-held radios have optional AA cell holders, and these cells could be used in those holders.
|Top: This is likely a NiCad cell, suggested by its capacity, lower that the typical NiMH. Ah is amp hours; with mAh used on smaller cells. 1.8 Ah is also 1800 mAh. Sub-C is 23 mm diameter by 43 mm, somewhat smaller in both dimensions than the C (UM-2) cell.|
Bottom: A NiZn cell in AA (UM3), mainly as a size comparison. Note that it is marked in mWh - milliwatt hours, rather than mAh. That would calculate as: 2500 / 1.6 = 1562.5 mAh. They yellow one conversely calculates thus: 1800 x 1.2 = 2160 mWh.
Not on the exam, capacity is a somewhat nominal figure as to how much current a battery could supply for an hour. A 7 amp-hour gel battery could theoretically supply 7 amps for an hour, although ratings are usually taken for a 20 hour rate, so 350 mA for 20 hours. Smaller batteries, or cells use mAh. A rating of milliwatt hours per cubic centimetre (mWh/cm³) or Watt-hour per kilogram is probably more useful to product designers than the typical hobbyist; although knowing lithium-ion has at least twice the energy per kg as lead-acid based ones might be handy to know if planning to hike up a mountain with your HF radio.
The mains supply, as well as various DC supplies, and high-power radio-frequency sources can cause serious or fatal electric shock.
Even the US 120 volt AC supply can deliver a serious, even fatal, shock. Injury types include heating of tissue, including burning; disruption of nerve and other cells; and involuntary muscle contractions, either making it impossible to let go of live wires, or throwing the person against a wall or sharp objects, causing further injury. One result can be either stopping the heart, or causing ventricular fibrillation. Touching an antenna wire or internals of an operating transmitter or amplifier can cause serious RF burns, damaging internal tissue.
In the United States, Canada, and Japan the Hot wire is Black, while the neutral is white. Earth is often plain green.
Many buildings now include RCDs or "Safety Switches", called a ground-fault current interrupter (GFCI) in the US. These interrupt the mains if the current flowing in the active / live is different to the neutral current, the assumption being the difference is due to current flowing via your body to ground. Plug in units are available if one is not fitted, as are ones to replace the plug on a powerboard, etc. These are based on the current transformer concept used in many clamp meters, with both live and neutral running through the core, and an imbalance triggering the breaker.
Three phase is a system where instead of just one hot / live / line / active swinging positive and negative relative to the neutral, there are three such hots, each taking turns to reach the most positive part of their cycle, one third of a rotation apart. In an Australian residential street often this is primarily a way to share the load across several conductors, but in larger motors, it improves the motors performance. In such cases instead of a star or Y (wye) connection working with a neutral, a delta connection, named for the upper-case Greek character, Δ. Here connections are between the phases, and the voltage between the phases is √3 ≈ 1.73205 times the phase to neutral voltage. In the US, where split-phase is not used, a three-phase system using 120 and 208 volts is used, NYC being an example. In Mexico they want 220 volts between phases, so the phase-neutral voltage is 127 volts. Where a delta arrangement is used, no neutral is run - why waste copper? Unlike in Australia where the whole street or industrial estate is powered by a large 3-phase transformer, with an earth-referenced neutral, a single industrial unit or, large doughnut shop might be fed from its own "pole-pig" transformers, and in this case it may be one of the corners of the delta which is grounded. Lighting, fans, heating, etc are selected for this voltage; and a smaller transformer inside the building is used for the 120 volt supply for office and point-of-sale equipment.
Flash burns, and electrical explosions can be fatal, so those working on high energy switchboards wear face shields and heavy woollen clothing.
Valve or tube receivers and test equipment often uses valves with around 200 to 300 volts DC for the anode / plate supply. High power transmitting valves may use around 2000 volts (2 kV), as do microwave oven magnetrons (also valves), and their supplies have the ability to supply a sustained, lethal current!
In the US Red is the second hot, (or second phase); and blue may be the the high-leg, 208 volts away from neutral, especially if marked or sleeved in orange, 240 volts from the other hots.
A Red hot and grey neutral means you are dealing with a 277 volt system; and brown, orange and yellow hots, possibly with a grey neutral, indicates 480 volts between the hots, There are also 347 / 600 volt systems, more popular in Canada.
One method to prevent electric shock is to earth the metal chassis of equipment, so should a live wire break away and contact the chassis, instead of it becoming live, meaning that if a person touches it while touching a water pipe or grounded metal equipment they get a shock; either an over-current fuse / circuit-breaker operates, or a Ground-Fault breaker (safety switch) kills the power. The earth is connected by a third pin on standard plugs. Most multiphase connectors also include an earth, as do 240 volt plus neutral connections, used for things like large linear amplifiers, meaning 4 pins - 2 hots, N & E. In the US system this wire is often plain green, or can be un-insulated wire inside walls. In Australia and Europe, it is usually green with a yellow stripe, meaning even a colour-blind person can identify it. It the US system the white wire is the neutral wire, and black the hot, or live wire.
For the North American domestic electrician working on industrial power, the practice of disconnecting the hot and neutral of the circuit being working on can be a fatal, or life-changing error, as loads on other phases can raise this disconnected neutral several hundred volts above earth. In Australia I understand it is usual to leave the neutral connected.
Earth symbol: ⏚
|This image shows a set of three "pole pigs", or transformers, supplying a range of accommodation businesses, restaurants, and residences in the "Fashion District" of Toronto, Canada. The upper three conductors are a three-phase supply, perhaps 13,800 volts. The conductors pass through a fuse each, and there may be over-voltage / lightning / surge protection. The exact arrangement is unclear, but given each transformer can only has a single high voltage terminal, it appears that they are in a "star" connection, with a single live connection, and a return via the low voltage neutral, but if the currents are well balanced, there should be little such current. In any case, if these are 10 kVA, then the current is only around an amp. The lower voltage connections then go to the various premises. It appears that the 600 means 600 volts. If so, large loads such as heating uses 600 volts, and small loads run off 600 to 120 volt transformers. Or maybe, there are 600 and 120 / 208 volt systems, given the two bundles of low voltage conductors.
Streetview shows that the transformers have been replaced, and are marked 347, indicating the phase to neutral voltage of a 600 volt delta system.
The CN Tower (La Tour CN) is behind. It supports the VE3TWR repeaters on 2m and 70cm.
A larger version of the photo is here
Streetview of the transformers: Augusta Street. You can change the year.
Australia follows the European and International standard for modern flexible cables, brown for active, blue for neutral, and green / yellow for earth. (IEC cables do turn up in the US, for things like PC power leads.) Older leads in Australia use red for active, black for neutral, and green for earth. In-wall wiring tends to use red and black, for A and N, with green or green/yellow for earth. Old cables had a bare earth, sleeved green at ends. Red-white replaced red-black cable going to switches, making the white the switched active, going to lights and fans. Three phase is often red, white, (darker) blue with black neutral (if needed), but European brown, black, and grey, with a (lighter) blue neutral is allowed. Red, yellow, blue was used once, with a black neutral. Here voltages are, in practice 240 / 415 volts, officially 230 / 400 volts. While the latter is also the official standard in the Europe, on the Continent the actual voltage may closer to 220 / 380 volts, the old standard.
The 433 volt warning sign seen on transformers in central-western NSW calculates to a 250 volt phase to neutral voltage. Western Australia used 264 / 440 volts once, sometimes at 40 Hertz. 264 / 440 volts is also used at 60 hertz on naval ships, in addition to 110 or 120 volts.
The old Russian standard, also used in China, included solid green as the second phase (!), with a green-yellow earth. This, and the above, indicates that colour codes must be read in context, and you shouldn't goof around with power, unless you know what you are doing, or have the guidance of an experienced person.
|At a transmitter / communications site in northern Victoria (Australia), this pole transformer is connected between two phases, hence the two large HV terminals. The additional devices are some sort of over-voltage protection devices, which would work in conjunction with the high voltages fuses (not shown) in the feeders. The spiral acts a a vibration suppressor on the feed wires. The output lines go into the conduit.|
Way off topic, but many farms and residential areas in Norway use a system with the 230 volt outlet pins being 2 phases, not Active and Neutral, this meaning that something like a large 3-phase pressure cleaner uses a blue (200-volt range) three-phase plug (3P+E), not the red 400 volt one used elsewhere in Europe.
Also not on the exam, but important if you have a separate high voltage DC supply for large amplifiers, and other valve / tube equipment, ensure that the two chassis are linked, as if the negative connection fails, the chassis / case of the transmitter, etc, will become live through the circuits within it, and if you touch it, you may become a "silent key", as deceased Amateurs are often called. Note that safety switches (RCDs or GFCIs) generally do not protect you from contact with high voltages beyond a transformer.
Contact with a high voltage connection is how the Australian pioneer Ross Hull VK3JU died, while working in the US. He was preparing to demonstrate a television receiver with a separate 6000 volt power supply, consisting of a 4400 volt pole tranformer connected backwards, and made contact with a wire between the transfomer and rectifier, while wearing headphones, which earthed him, completing the lethal circuit. The pole transformer had an utterly excessive current capability, which contributed to his death. In most cases the high voltage (EHT) supply in a CRT TV or monitor may have a higher voltage, but can only supply a very limited current, which is unlikely to cause serious injury.
Meanwhile, one Sunday morning the local news included the tale (or tail?) of a guy in Perth, WA, who continued the practice of dispensing, um, "used beer" onto the roofs of passing trains from bridges; AFTER conversion of the network from diesel to overhead 25 kV AC! Apparently he survived with "severe abdominal burns". The voltage is high enough to jump any breaks in the stream, even if the 600 volt of third rail systems isn't.
While working on electrical systems which are either potentially electrically live, or known to be live, a range of insulated and tested tools are available. Examples for general use are screwdrivers and pliers. Screwdrivers have insulation down the shank, with only 10-15 mm of metal exposed. These are often sold as "VDE Electrical Screwdrivers", for the German certifying institute.
For live working, which requires significant training, tools include fixed and adjustable spanners, socket sets, hex (Allen-style) keys, hacksaws, off-set screwdrivers, regular screwdrivers, and nut-drivers, along with insulating sheets or "blankets" and clamps for them.
The most famous brand is Sibille from France. Also French are SAM and CATU. The appropriate standard is IEC EN 60900. The classic orange Sibille drivers have a white insulation covered in a hard orange PVC. Thus damage to the tool becomes evident, with white plastic becoming visible.
Another standard is ASTM F1505-16(2021), with Klein being a US manufacturer using this standard. Fluke also now make drivers.
The red tinted acetate handled ones sold by Stanley in Australia appear not to be certified.
The oldest is the blade, flat, or flat-head driver, dating to at least 1475. Many traditional driver have a flared tip, while some have straight-sided blades. The latter may be refered to as "electrician's screwdrivers", as they allow the tip to fit into recessed terminals; however, be aware that if these are not insulated you should only use them in situations where there is no possibly that dangerous voltages are present. Several designs have exposed metal passing through the handle, some being traditionsl woodworking tools. The second are those with the metal tang ending in a flat striking cap. "Engineer's screwdriver" is just a marketing claim.
Tips of these drivers, or "turnscrews" are specified by width of blade × its thickness, such as 5 x 0.8 mm. In some cases the width in fractions of an inch is specified instead.
Then came the square Robertson or Scrulox, invented in Canada in 1906. A relative is the hex socket head, operated by Allen keys and straight or ball-ended drivers.
There are several cross form tips. The first was Phillips, starting around 1935. Frearson is a variation. The Pozidriv and Supadriv are European versions which resist "cam-out", a problem with Phillips. JIS Type S is a variation used in Japanese cameras and at least some radios from there. These are listed by number, getting larger as they increase; 1, 2, 3 trending from the domestic to the industrial. 0 is small electrical, and 00, 000 are used inside watches and lenses. PH0 (Phillips 0) and PZ2 (Pozidriv 2) are examples Moody Tools sell several kits of JIS drivers.
Screws with hexagonal holes in the head are fairly common in various equipment. The most famous are 4 mm versions in Swedish flat-pack furniture. Most often they are operated using Allen Keys, or copies, but screwdriver and power driver bits are available too. Hex screwdrivers are great for "deconstructing Ikea". Grub screws, and most set screws, have no head, but rather a hex hole smaller than the diameter of the screw. A typical 3 mm one requires a 1.5 mm key. In Ham radio they are used to hold wire whips in vertical antennas, while allowing adjestment for low SWR. There are also fractional inch versions.
"Nut-drivers" fit over hex nuts, for low torque or initial driving, with millimetre and fractional inch versions available.
There are then a bunch of "security" designs, such as Hex head with a pin in them, requiring a bit with a hole. Likewise there are security version of the 6-lobe Torx head. Tri-point and Tri-wing are others. Bi-pin is another. Pentalobe is a method Apple use to impede repair of their overpriced devices. Thankfully, Chinese tool makers are quick at providing solutions. They do however have the benefit of making opening the sealed area of hard-drives more difficult, as this is very much not a good idea unless it is no longer of use, and you wish to see the insides.
Various sets of bits are available for regular and "security" bits, as are official and unofficial drivers.
To counter cam-out several manufacturers offer drivers with roughened tips, such as Wera'a Laser Tip: Kraftform Plus Series 100
Many electrical terminals use a compromise head which accepts both blade and Phillips or Pozidriv drivers. As neither driver may provide ideal fit, several manufacturers offer "+-" drivers which they clain fit into the recess better. The annoying aspect of this is that you have to ensure the tip is correctly orientated. As these recesses may also accomodate Roberstson, these may be the a better option, as is ECX, a combined Robertson and blade tip. ECX drivers are sold by Klein, and by Milwaukee.
If doing something like fitting a plug with screw terminals, try to have it on a bench or other surface, rather than in your hand, to avoid "perforating your palm" as a Telecom instructor used to say. Likewise, be careful when using prying tools or "spudgers" to open consumer electronics, etc.
Drivers with handles designed to fit the hand more naturally are both more comfortable to use, and allow the user to apply a greater torque. That said, they can also allow you to break screws, or strip threads.
The opposite are ESD-safe tools. These are drivers with a degree of conduction across the handle, and between the handle and the blade, to prevent static build-up and discharge. Cutters, pens, brushes, and other tools are availabe for working in ESD-safe work areas. These precautions protect CMOS and related electronic circuitry, including PC parts from damage due to electrostatic discharge. Wrist straps, which ground workers through a 250 kΩ or 1 MΩ resistor are also necessary, teh latter required in 230 volt countries to ensure current flow is limited in-case of contact with the mains. ESD-safe tools and earthed wrist straps should NOT be used when testing or adjusting equipment using mains or similar voltages.
ESD-safe storage bins and trays are also available, typically made from carbon loaded plastic, which is thus black. Parts are boards are often stored in nickelised plastic bags. While not providing full protection, pink plastic bags and foams do not generate static. Even ESD-safe black waste bins are available, along with pink plastic liners. Why pink? It is easier to do a pink tint than a full red one.
When a few 10s of dollars can buy a safe meter, extremely cheap ones do not make sense. And while AliExpress is great for Sausage Dog socks and generic components, I wonder about the safety of some of the cute meters which they sell. I was going to suggest thet they might be OK for low voltage stuff (9-volts battery powered), but remember that a marine style or deep cycle battery which can power a station for emergency comms is capable of providing large fault currents.
In addition to voltage and CAT rating between probes, the voltage above ground for the common probe is also subject to a rating.
And forget slipping over on a bit of BBQ onion, a certain hardware selling warehouse is spuiking the 1000 V dc and 750 volt ac ratings of some low dollar meters, with no CAT numbers, the higher cost one shown on the 20 volt range, but with one lead in the UNFUSED 20 amp socket. Perfect (NOT!) for testing a large, gassing starting battery from a heavy diesel SUV. 💥 Their Klein one is not great value, but should be fine if you have an urgent need.
If replacing leads, or upgrading, remember that voltage, current, and category ratings on these must be appropriate to the circuits being tested.
Lightning is the discharge of very large static charges, either between clouds, or between clouds and ground. It contains wide-band radio frequency energy, especially around 1 MHz. Towers and antennas can be struck by lightning, due to being high, and "pointy". Voltages and currents are very high, and significant effort must be put into managing these. Larger towers much be grounded using multiple ground-rods, well spread out, and heavy conductors. Three or six runs of cable, with several rods each is a good ground. Feed-lines must be grounded, and fitted with over-voltage protection devices, such as manufactured by PolyPhaser, not some random unbranded one from a truck-stop's CB section. The RF nature of lightning means connections must be heavy and direct, without sharp corners. Around US$60 is affordable protection for expensive equipment.
An example: POLYPHASER IS-50NX-C0. A SO-239 version also available, as are units for higher power levels, and ones used when DC power needs to be passed to mast-head amplifiers, tuners, or band-change switches.
A new question emphasises the need to link earth stakes with heavy conductors or straps. A strap using the same mass of copper per metre has a greater surface area than round cable, and this surface area is useful for carrying away lightning energy, with its RF content.
Using grounded antennas, such as folded dipoles for VHF and UHF means that if a the antenna itself is struck, much of energy goes to ground, is also good practice. Lightning CAN strike the side of a tower, not just the top, although a metal rod above the highest antenna can be beneficial.
If you have a metal roof, grounding it is also a good idea. Also, better TV antenna shops sell grounding blocks for TV antenna coax, just cut the cable, put on two F-connectors to connect to the block, and run a heavy wire to your station ground, or a ground rod also connected to this.
One professional communication friend who lived on an ironstone ridge had a strip of earthed copper strip running around the wall in his ham radio room, just in case lightning came looking for his well grounded radios, and found him in the way through. Instead, the current would have gone to earth via the strip and its ground connection.
It is a good idea to disconnect antennas at times when electrical storms are expected. Unplugging ADSL / VDSL lines, including (for VKs) the "Fraudband" / FTTN version of the NBN. If only there was a way to transmit data through something insulating like glass. Oh, optical fibre, like the smart Kiwis have.
Amateurs use various masts and towers to elevate antennas to provide longer range communications, or to act as antennas on lower frequency bands. Obviously, falling from such a structure will result in a sudden, and highly problematic stop at the bottom. Thus a safety harness is required, with the benefit that it allows both hands to be used while working. Good harnesses have two straps or ropes with hooks so that the climber is always attached while ascending or descending. They also have straps over the shoulders. All workers, including those on the ground, should wear a helmet and safety glasses. Work must cease whenever there is the potential for lightning anywhere nearby. In general, all systems should be shut-down, where possible.
Crank-up towers mean that the antenna can be worked on at a lower level, and the tower retracted during storms. There are however a range of hazards related to these, and requirements for safe winches, which cannot rapidly un-spool. These must not be climbed while elevated. Be aware that a galvanised pipe or tube can corroded internally, and be little more than rust and galvanising, but look good.
Towers must be grounded effectively. The exam specifies a ground rod bonded to each tower leg, and to each other. A friend has a large tower, and runs two cables from each of the 3 legs, and each has up to 7 rods, with a 2 metre spacing between each rod. He also has Polyphaser surge protection on feed-ins. This is the extent of protection required to have equipment survive a strike. He has also grounded the metal roof of the "shack".
While there is no proof that radio signals have negative health effects unless the signal is so powerful it causes heating of body tissues, there are a range of exposure limits.
At a club meeting discussing this, the lecturer ran through calculations to demonstrate that for HF signals, at a power of 100 watts into a dipole, as long as it is not possible to physically touch the antenna, meaning it is beyond 2.5 metres, the RF field will be at a level considered safe.
The ARRL VEC has provided this useful information sheet.
One thing it indicates is that the Maximum Permissible Exposure is lowest in the VHF bands, 30 to 300 MHz. Just remember, this includes 6 metres (50 MHz).
At VHF, UHF, and in the microwave bands, longer yagis, along with dish antennas, can generate high field strengths, potentially in excess of the number in the standards, in the direction in which they are pointing.
One method to reduce the field strength in your neighbour's yard or house is to raise your antenna, so the signal passes overhead harmlessly. This also reduces TV and Radio interference for the same reasons. Of course, haters who don't like antennas (or councils and "home owner associations" who ban them) mean it may be necessary to quietly run your HF antenna wire along inside a wooden fence. These can be quite effective. Any "exposure" is therefore entirely there fault.
If you do put up a conspicuous antenna, putting it up before you get your licence, or before your HF radio arrives, etc, if someone claims you are interfering with their TV, you can point out that you have not been operating yet, or that you have only been listening.
|International Standard Non-ionising Radiation symbol.||Global ionising radiation symbol.|
Also called a Trefoil, for the 3 lobes.
|Internal markings for radiation sources, warning the thief or|
scrap-yard worker to cease disassembly, and evacuate the area.
|US ionising radiation symbol, which originally had a blue|
background. Magenta was chosen as it is unique in safety signs.
The term "duty cycle" applies to many electrical and other processes. Often it is expressed in percent, although a ratio (such as 1:3) is an option. It can also be expressed as, say, 20 seconds each 10 minutes for the high current range on a multi-meter, where the shunt heats when current is flowing, not only potentially damaging the equipment, but affecting accuracy. Suppose you calculate that the maximum power at which field strength complies with the rules and your fence-line is 1000 watts if you transmit constantly, but you typically only transmit 50% of the time in a conversation, then the safe limit doubles to 2000 watts, meaning 1500 watts (legal power in most cases) is fine.
For a repeater you need to allow a 100% duty cycle, as a club net can cause it to transmit almost contantly for an hour or more.
Some questions use an old British unit, the foot. This is 12 inches long, so is defined as 12 x 25.4 mm = 304.8 mm, or 30.48 cm, or 0.3048 metres. Thus there are 1 / 0.3048 = 3.28084 feet in a metre. A single apostrophe indicates feet, a double one inches, thus: 3' 3⅜", this being 1000.125 mm, a hair's breadth over a metre.
Thus a 20 metre band half-wave dipole, at around 10 metres long is rounded to 32 or 33 feet, depending on the whim of the examiner.
While a lot of consumer electronics has gone "lead free" using nearly pure tin, rather than tin-lead (Sn-Pb) solder, hobby electronics often uses lead containing solder. Also, as pure tin grows whiskers which can cause short circuits, lead-free equipment has reduced reliability over the lead versions, and is banned in medical and space electronics, and emergency related equipment. If using lead based solder, make sure you wash your hands after soldering. Also, avoid breathing the fumes from the flux which activates when solder is heated. A filtered fume extraction fan may be a good idea.
WSW Solder Wire 0.8 mm, 100 grams is a lead free solder suitable for most hobbyist jobs.
Small petrol / gasoline motors, including as used in generators which may be used at field day and emergency support events are generally very polluting, having no pollution control gear. Of most concern is carbon monoxide (CO). While quite reactive, it is odourless, and invisible, but it is absorbed into the bloodstream, reducing oxygen uptake, resulting in flu-like symptoms, and potentially death. Thus they need to be operated outside. As they tend to be noisy, a long, high-quality lead means the generator can be placed away from the operating position. Inefficient combustion of hydrocarbon fuels and wood, including when used for heating or cooking, also generates CO. Low cost CO detectors, some looking similar to a smoke detector, are available at many hardware stores.
While petrol / gasoline may not be quite as easily ignited as Hollywood would like you to believe, clearly smoking while filling a generator, etc is rather unwise, as would filling up near a naked flame, or someone griding metal. Diesel is combustible rather than flammable, but again care should be taken. Note that ethanol flames can be difficult to see, and generate little smoke. I am not sure how E85 fuel behaves in this regard.
Over the coming years, in California new gasoline yard equipment, and eventually new gasoline generators will be banned. While solar panels and large, probably lithium, batteries may be idealised replacement, compression ignition (diesel / biodiesel) will likely be used; and depending on the wording of the law, spark ignition engines running on propane (LPG), CNG, alcohol or other biofuels, etc, instead of gasoline could be the used.
Many hams engage in wood and metal work to build cabinets for projects, and shelving and the like for their station.
Use the correct tool where possible, and to follow relevant safety advice for the tools being used.
Safety glasses are inexpensive. They can also protect your eyes while clipping component leads, and while soldering. Shooting glsses are perhaps suitable too.
Be careful when using spanners than they do not slip off the nut, and also be aware to avoid your hand hitting something which will injure it if it slips, or the nut suddenly becomes very loose once it "cracks".
These are actual exam questions, from the published NCVEC Technician pool, relevant for exams up to midnight on June 30, 2026.
Which of the following is a safety hazard of a 12-volt storage battery?
A. Touching both terminals with the hands can cause electrical shock
B. Shorting the terminals can cause burns, fire, or an explosion
C. RF emissions from a nearby transmitter can cause the electrolyte to emit poison gas
D. All of these choices are correct
The typical (lead-acid) 12 volt rechargeable battery is designed to be able to start a large capacity, high compression, automotive or marine engine, which requires a lot of current, so get a spanner between the positive terminal and the bodywork of a car, while the negative strap is connected, and very large currents will flow, with the potential that sparks will cause hydrogen gas to explode. Splattering molten metal, overheated wires, etc can cause thermal burns; and if the case splits, splashing or spraying acid will cause chemical burns. Overheating wires can start a fire too. Answer B.
The voltage of such a battery is generally too low to cause a shock, but if you have deep scratches on your hands, and pick up a battery with your thumbs around both terminals, you could experience enough pain that you drop the battery, meaning acid everywhere! Submarine batteries pose the risk that seawater, containing sodium chloride, mixing with battery acid would produce chlorine gas, killing the crew.
What health hazard is presented by electrical current flowing through the body?
A. It may cause injury by heating tissue
B. It may disrupt the electrical functions of cells
C. It may cause involuntary muscle contractions
D. All of these choices are correct
A sustained electrical current of a moderate to high level typically causes heating or burning of tissue, messes with your cells, and makes your muscles (including heart) contract, all causing injury. Answer D.
One factor is the duration, so a high voltage but current limited short duration pulse from an electric fence really only causes short-term pain, unless it is during a night-time rural roadside "comfort" stop, when I am told it is the absolute opposite of "comfort"!
In the United States, what circuit does black wire insulation indicate in a three-wire 120 V cable?
C. Equipment ground
D. Black insulation is never used
Hot is black, answer B.
What is the purpose of a fuse in an electrical circuit?
A. To prevent power supply ripple from damaging a component
B. To remove power in case of overload
C. To limit current to prevent shocks
D. All of these choices are correct
Fuses open due to current overload, helping to prevent fires and other damage, answer B.
Why should a 5-ampere fuse never be replaced with a 20-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
Suppose a device is designed to use 4 amps, and a short in a transformer output, or a partial short of a heating element, or a stalled motor draws 15 amps, then excessive heat will be dissipated, and instead of the fuse operating, "exciting" things such as fire happen! Answer C.
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. Install mechanical interlocks in high-voltage circuits
D. All of these choices are correct
The answer they want is D, all choices.
Three wire cords, in other words a cable and plug with an earth connection is necessary when using equipment with a metal case, or when it contains a metal framed transformer; unless the equipment is approved with "double-insulated" markings, or it is powered by an approved plug-in power supply or "wall-wart". Some amateur equipment has an external grounding terminal, and these can be connected via a braid or strap to a copper trip at the back of your bench or desk, and then connect this to ground rods outside, making sure this system is "bonded" or connected to the house mains earth. Lightning protection should also be connected to this common earth. A mechanical interlock is a device within a valve based power amplifier which shorts the high voltage supply to ground, or otherwise disconnects it, should the equipment's cover be removed.
The GFCI / RCD / safety switch has been removed, but is a good idea.
Which of these precautions should be taken when installing devices for lightning protection in a coaxial cable feed line?
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
Lightning protection devices are designed to short over-voltages on the inner of the coax cable to the grounded coaxial shield, and to ground. The usual place for them is the point at which the coaxial cables enter the building, on a common metal entry plate, answer D. The protectors need to be rated for the power the station transmitter puts out, so they do not arc-over on transmitter power. Switches in the ground line are a stupid idea, and would either arc-over, be welded shut with the first strike, or be blown to bits, probably along with your radio...
What safety equipment should always be included in home-built equipment that is powered from 120V 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
Applying to mains powered equipment of any voltage, fuse(s), or a suitable circuit breaker, should be placed in the hot (live / active) conductor(s), answer A. Not safety equipment, but inductors and/or capacitors of suitable rating can be used to filter either noise coming in on the mains, or RF energy leaving the device via the mains lead.
What should be done to all external ground rods or earth connections?
A. Waterproof them with silicone caulk or electrical tape
B. Keep them as far apart as possible
C. Bond them together with heavy wire or conductive strap
D. Tune them for resonance on the lowest frequency of operation
All grounds must be bonded (joined) together with heavy wire, or better, heavy conductive straps, answer C. This includes linking the power ground / earth to your radio equipment ground system. Waterproofing is generally not required.
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
High current flow causes heating due to ²R losses. Charging lead-acid batteries is an "exothermic" chemical reaction, and so generates additional heat. Heat also causes chemical reactions to be more active, and causes increases in gas pressure, swelling of cases, and potentially causing over-pressure explosions, while sparks can set off explosions in hydrogen gas, produced during charging and discharging. Answer A. "Memory effect" primarily refers to Nickel-Cadmium (NiCad) cells, which are repeatedly charged after being lightly discharged. This does not apply to either lead-acid, or lithium technologies. Cell reversal can occur in over-discharged NiCads if one cell is under-capacity.
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 the charged stored in large capacitors
Capacitors store energy, and if the voltage is high, this means an electric shock is possible, answer D. Large (broadcast) transmitters often have interlocks on the covers, which short the high tension (high voltage) to ground, and blow the HT fuse; note Ham linear amps do NOT have this protection. B appears to allude to collapsing magnetic fields in relays and other coils zapping transistors. Static discharges won't damage earth wiring, but can damage some electronics, such as computer boards.
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
Tools, antenna parts, nuts, and bolts can be dropped from the tower. If they hit a cross-bar, etc, they can then bounce horizontally at high speed. Thus both helmets and safety glasses should be worn at all times by both climbers and ground crew. It is also possible for the climber to bang or cut their head on sharp metal, etc. Answer C.
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 (fall arrester) and safety glasses
D. All of these choices are correct
A climbing harness will stop you turning into a blob of strawberry jam at the base of the tower if you slip, and safety glasses protect from loose objects, flakes of rust, etc; so answer C. Wrist straps are to prevent static discharge into CMOS electronics while working on un-powered or low voltage equipment. Un-grounding the tower is just silly, and would not prevent lightning strikes, etc.
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
If you slip, even while wearing a harness, you may be injured and need assistance from emergency services, so a helper or observer should always be present, so answer D.
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
If either an antenna element falls on an electrical wire, or the wire falls onto the antenna, high voltages can enter the radio room along the feedline, and obviously, you could get electrocuted if a part of the mast, or an antenna contracts the live wires when you are working. The US tends to use 6 to 14 thousand volts on overhead lines, feeding small transformers feeding each house, or a few houses, so rather nasty voltages. Answer C. Again, grounded wrist straps are not for this sort of work, and amateur radio towers generally should be grounded, as they usually support antennas, rather than being the radiating element, as in AM broadcasting.
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
Suppose you have a mast with a pivot at the base, to which we have affixed out antenna(s) and feedline(s). We may be able to lift the end, perhaps with help, but as we walk along it, towards the base, the force we need to use to lift it becomes greater and greater, as we loose mechanical advantage; and even if we have someone on the ground pulling on a rope to help lift, most of the force is trying to pull the mast along the ground, rather than lift it. If only we had a crane to provide vertical lift... Attach a second, strong piece or timber or metal to the pivot point, maybe half to 2/3 the length of the mast, with a few metres of rope going to the mast, and one going to the team-members pulling, or maybe to a reliable winch, and pull on this, and the force of directed in such a direction that it is efficiently lifting the mast. Another arrangement is a pipe, pole, or lattice section attached to the already erected section of a tower to lift the next section into place. Answer C.
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
For various reasons, including age, metal fatigue, ice-loading, or falling tree branches, an antenna or the mast supporting it can fail, and if it contacts mains wires, the user could be "electroluxed", especially if you are doing something like holding a metal hand-held radio connected to an outside antenna, with no earthing at the entry point. Clearly, half a wavelength could be 80 metres or more, or it could be 12 centimetres, so that is not a sensible answer, and A and B are also variable. Thus D is the only sensible answer, 10 feet being 3.048 metres. As power lines can be electrically noisy, due to poor quality switch-mode power supplies, motors, arcing thermostats, etc, keeping antennas significantly further away is a great idea. Note also that older insulated power feed-in cable can have cracks in its insulation
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 not be climbed unless retracted or mechanical safety locking devices have been installed
D. All of these choices are correct
Some ham radio towers consist of nested triangular or square lattice tower sections. These use a winch, often hand-cranked, to lift the inner sections, telescope fashion. These allow antennas to be worked on at lower level, as well as allowing them to be lowered to during storms, or keep neighbours happy. In Australia, at least, it is illegal to use a crappy trailer-boat winch, where if the ratchet detent is released, the whole thing collapses to the ground, but never-the less, everything is hanging on a single cable. Thus C is the answer - only climb while the tower is at its lowest, or fully retracted position. The exception is when there are mechanical locking devices to prevent the sections telescoping down. All towers should be grounded, and perhaps if near an airport, painted. (The prohibition on painting applies to ladders, as this stops cracks and splits being visible).
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
Each tower leg should be grounded, and if soil depth allows, long earth-rods should be used. The desired answer is C. Ideally there should be a very heavy cable running from each leg, with several earth rods, each around two metres apart. The idea of having the rod in close proximity (30 cm) of the tower is pointless, as the base usually has some grounding effect, especially if a course mesh of copper wires are laid in the bottom of the hole before the concrete is poured. Rods much closer than 2 metres apart have little benefit over a single rod, but three (or more) runs with correctly spaced rods is a great idea.
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
US street poles can have up to 13,800 volts on them, and down-under 11,000 volts, sometimes 22,000 volts, so not something you want to go banging a large hook into (and potentially causing bits to fall off). You don't know when something like a truck crash will cause the higher voltage lines to fall, and you really don't want those wires landing on your antenna, so C. While not the safety reason in the desired answer, it is true than proximity to such wires may increase interference; and secondly, it isn't your pole, so leave it alone... That said, if you can pay to get the supply authority, or others, to stand a couple of their tallest poles on your rural property, there are some great antenna options, such a curtain arrays and large rhombics.
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
You may have noticed that I said that lightning is radio-frequency current, and as such, heavy, direct connections are needed, and that sharp bends need to be avoided, so answer C. There is nothing wrong with using insulated wire or insulated strapping. All grounds must be bonded, otherwise if your tower is hit, there can be a large voltage between your radio case and the case of your computer, etc. Cable-TV lead-ins, TV antenna cable and satellite TV cables should also be connected to the same ground, as separate grounds are a major hazard. Bonding grounds is also required by electrical codes around the world.
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. UL recommended practices
In the US, states, counties or cities select which electrical standards apply, usually a version of the National Electrical Code (NEC), but they do make their own interpretations, etc. Answer B. In other countries, the local standards must be followed, such as the Australian and New Zealand common standards.
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
Loops to prevent moisture entering buildings are great in coaxial cable and things like antenna rotator control cables, but in earthing systems they add inductance, which can limit the earth current, thereby raising the voltage on the protected equipment, etc. Again, tight bends are bad, so C, short and direct, gets you the mark.
What is the purpose of a safety wire through a turnbuckle used to tension guy lines?
A. Secure the guy if the turnbuckle breaks
B. Prevent loosening of the guy line from vibration
C. Prevent theft or vandalism
D. Deter unauthorized climbing of the tower
Turnbuckles consist of two eye-bolts, one with a left-hand thread, which both screw into a central piece (or frame), and rotating this piece tightens the guy lines. Wind makes guys vibrate, and this could lead to the turnbuckle loosening, perhaps to the point the point these unscrew totally; potentially allowing the tower to collapse. A safety wire prevents this loosening, answer B.
This can consist of the two ends of the guys looped back and joined with small U-bolt based clamps.
What type of radiation are VHF and UHF radio signals?
A. Gamma radiation
B. Ionizing radiation
C. Alpha radiation
D. Non-ionizing radiation
Gamma and Alpha are both ionizing (or ionising) radiation, but radio signals are non-ionizing radiation, so D.
Which of the following frequencies has the lowest value for Maximum Permissible Exposure limit?
A. 3.5 MHz
B. 50 MHz
C. 440 MHz
D. 1296 MHz
The VHF bands, which include 50 MHz (6 metres, the "magic band"), have the lowest MPE, so answer B. You probably just need to memorise this rule.
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
For the VHF bands if your power is above 50 watts PEP at the antenna, where it counts, answer C. 1500 watts is legal lower, unless another limit applies, and certainly anywhere near this, on any band, assessment must be carried out.
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
The level of exposure rises with the power of RF, and the allowable level varies with frequency; field strength drops rapidly as distance increases (double the distance, quarter the power); and the radiation pattern of the antenna also has an effect; so D all are correct.
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
The body (basically a big bag of salty water), absorbs RF to a different extent at different frequencies, so D.
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
Manual calculations, following the document mentioned; computer modelling; and measurement using calibrated equipment are all valid, noting that this is quality equipment, not the simple relative measurement some CB SWR meters may include; so answer D, all choices.
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
Radiation poisoning is related to very high levels of ionising radiation, say from a very serious nuclear accident. While poor quality TVs can suffer interference from Amateur signals, a stupid person interfering with your antenna while you are transmitting won't cause TVI, unless you count the loud swearing as they suffer a painful RF burn, answer B.
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
It is the location of the antenna, not the transmitter which matters, so A. Increasing duty cycle increases average exposure.
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
The FCC really does NOT want to know what you are doing... Poor SWR does not increase exposure, although making sure your radio sees a reasonably low SWR is a good idea. It is B, that if you change antenna, or buy or build a linear amplifier, or even upgrade your coax to reduce loss, field strength can increase beyond the official limit, so you should re-evaluate compliance.
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 feed line loss
D. It takes into account the thermal effects of the final amplifier
Changing duty cycle does not affect the peak power, but the average, answer A. While not the "why" in the question, feedline losses are a part of any field strength calculations, but thermal effects in the amplifier aren't related to RF exposure, although duty cycle is an issue with some ham-grade or two-way transmitters (that is, their final amplifiers), compared to broadcast units, designed for 100% duty.
What is the definition of duty cycle during the averaging time for RF exposure?
A. The difference between the lowest power output and the highest power output of a transmitter
B. The difference between the PEP and average power output of a transmitter
C. The percentage of time that a transmitter is transmitting
D. The percentage of time that a transmitter is not transmitting
In a typical conversations you transmit about 50% of the time, and listen about 50%, unless you have a full-duplex telephone-like system. Thus duty cycle is 50%. In a group you might only operate one minute in six, about 16% duty cycle. A repeater can transmit up to 100%, but something like a weather station might send data for a few seconds every few minutes, so a very low duty cycle. This is answer C.
How does RF radiation differ from ionizing radiation (radioactivity)?
A. RF radiation does not have sufficient energy to cause genetic damage
B. RF radiation can only be detected with an RF dosimeter
C. RF radiation is limited in range to a few feet
D. RF radiation is perfectly safe
RF radiation does not have the energy to damage the DNA and other genetic material, so answer A. RF energy can be detected by electronic equipment, even a simple RF signal diode and a cheap mechanical meter movement, although more complex electronic systems exist, called "densiometers", the term dosiometer referring to small badges containing a patch of photographic film, which is "fogged" by ionising radiation. It is actually beta particles (one type of ionising radiation) which are stopped by a few feet of air, with gamma waves not going much further. Very high field strengths can cause heating of tissue, just as a microwave oven heats food, and looking into a waveguide carrying high power microwave signals can cause heating in the eye. At lower levels, there may not be health effects which can be proven, but it is difficult to entirely prove a negative.
Waveguide is an alternative to coaxial cable for use at microwave frequencies, where coax is very lossy. They are rectangular, round, or corrugated elliptical metal tubes, the last one semi-flexible, a few millimetres to maybe 12 cm in width, and can contain high level RF energy. It is used in radar, microwave radio towers, and some satellite dishes.
Sign on microwave / radar gear: "WARNING! Do NOT look into waveguide with remaining good eye!"
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?
A. 3 times as much
B. 1/2 as much
C. 2 times as much
D. There is no adjustment allowed for shorter exposure times
Say you calculate 800 watts is an acceptable level, then 1600 watts would be acceptable with the 50% duty cycle in the questions, so 2 times the power, answer 2, meaning 1500 watts legal power is fine, and the limiting factor. If you calculated 500 watts, then your would be only allowed 1000 watts at 50% duty cycle. Answer C.
On to: Regulations 1
You can find links to lots more on the Learning Material page.
This has taken a fair bit of work to write, so if you have found this useful, there is a "tip jar" below.
Written by Julian Sortland, VK2YJS & AG6LE, August 2022.
Tip Jar: A Jefferson (US$2), A$3 or 3 Singapore Dollars. Thanks!