No matter what kind of operating you do, sooner or later you’ll need a “gadget” that isn’t readily available commercially.

Maybe you’ll need a special switch or an interface between connector types or to a radio accessory port. After making one or two of these, you might develop a taste for homebrewing of the electronics variety! Many hams started small and wound up making equipment that rivals professional quality.

One thing you’ll learn quickly, though, is that nice-looking metal enclosures are surprisingly expensive. Even small boxes can cost as much as the electronics inside them.

To keep the cost of building reasonable, I’ve learned to make use of less-expensive materials to make my own, particularly when building something for the first time or just trying out an idea. Low-cost materials encourage prototyping and trying out alternatives—you can then use the money saved on a better enclosure for the final version. Or you might find the inexpensive alternative to be a fine permanent solution.

Here are some tips and tricks that have served me well.

Basic Boxes

One of your most useful discoveries will be that specialty products sold for electronics are often quite a bit more expensive than a very similar product made and sold as consumer and commodity products.

This is true for more than just metal boxes!

If you can use something made and sold by the zillion, you’ll save a lot of money, especially if you are willing to accept a different shape or can modify a commercial product. For example, electric fence insulators and PVC pipe, or conduit fittings, are much cheaper than ceramic insulators!

My favorite source of project enclosures is products made for electrical wiring parts, especially the junction and switch boxes. You can see several examples in the photos below. The boxes are sturdy and cheap, and they are galvanized or plated. They make good shields since they are metal, which is extra important in the ham station where RF is present everywhere.

Most of these boxes have convenient holes for grounding and bonding connections. The boxes are inexpensive so if you make a mistake or decide to change a layout, you can start over very easily and cheaply. Ganged boxes can be joined together to make larger boxes. There are quite a variety of these metallic boxes available online or in the electrical section of your local hardware stores.

Electrical boxes have round “knockouts” for attaching conduit and cable clamps. There are three common sizes specified as “trade sizes” of 1/2, 3/4, and 1 inch. They mount in the body of the box with a small tab. Push on the knockout with a screwdriver to bend the tab, then flex it back and forth to break the knockout free. Threaded conduit clamps mount in the resulting hole. There are a large number of clamps and parts that mount in knockouts for different purposes.

Rubber grommets are available to avoid chafing a cable.

The conduit clamp is threaded and mounts on the box with a large nut similar to a toothed lockwasher. Tighten it by tapping on the nut’s serrations with a screwdriver while holding the clamp with pliers. The clamp is flat-sided to capture electrical cable and is tightened with screws. The clamp will also capture the flat side that is present on most threaded RF connectors. 

Smaller connectors, such as phono or phone plugs, will probably require a drilled hole or you can enlarge a pre-drilled hole. Another option is to use a pair of large flat washers to both fill the hole and hold a threaded connector.

If you are running coax or other shielded cable through the clamp, create a pigtail from the shield braid or wire that is long enough to wrap around one of the clamp screws. This allows you to make a good connection to the metal box.

Another nice thing about electrical boxes is that they are heavier than a similarly-sized aluminum or plastic box. This helps keep them in place when cables are attached or if controls or switches mounted on them are used frequently. Rubber or plastic stick-on feet work as well on steel as on aluminum, but be sure to clean the surface first since there may be some lubricating residue left from the manufacturing process.

Noise Pickup

A caveat about using plastic enclosures—unshielded enclosures for RF projects can allow common-mode noise to get into feed lines. (Noise refers to any unwanted signal picked up on the outside of the shield.) Noise currents flow to the end of shield on the outside and then enter the cable as a differential-mode signal.

If you can’t shield the enclosure, consider feed line chokes from ferrite cores on the cables to block the noise currents.

Surplus and Used Enclosures

An often-overlooked source of project materials is surplus, overstock, or used equipment. Popular online auction websites are a good place to find enclosures and other materials. Local sources include Craigslist and free “buy nothing” sites organized by location. You will also be able to find “service pulls,” which are equipment and devices designated as past their service life. You may have to buy several to get the best price, so share the savings with friends!

Along with hamfests, flea markets, and garage sales often include electronic gear that can be stripped for parts and hardware, with the enclosure left to be reused. Equipment cabinets for outdoor use, like the fiberglass box I bought surplus, are usually weatherproof, too.

Data and cable TV service boxes are widely available as surplus and usually have a basic weather-resistant cable entry. They are mostly plastic and unshielded but make good protective enclosures for cable connections and smaller devices.

The photo below shows such an enclosure used to hold a control circuit for switching a pair of receiving loops. Feed lines come in through the foam inserts at the bottom.

Obsolete instruments and equipment are usually constructed with solid, high-quality cabinets that cost a lot new. Panels and other metal parts can be cleaned in the dishwasher. Disassembling this type of equipment is an education in how electronic devices are assembled and provides a lot of useful hardware.

Taking this stuff apart is a great project for beginning electronics and ham radio hobbyists to build expertise (and a junk box)!

Holes in used enclosures can be filled with metal “hole plugs” that snap in place. Large holes can be covered with a piece of unetched PC board material or scrap sheet metal to maintain shielding. Older outdoor enclosures, particularly fiberglass or plastic, should be painted with automotive primer to protect and seal the surface.

Food and Novelty Containers

A popular activity in the QRP community is to build gadgets in the snap-together tins that hold Altoid mints. After all, they say, if the mints themselves were “curiously strong,” then why not the signal from a transmitter built in the same container?

There are even prototyping kits based on the tins such as this product from QRPme.com.

Don’t expect heavy-duty use from these lightweight, nearly disposable items. They are often painted and need to be scraped or sanded to bare metal around connectors and any overlap joints you expect to act as shielding. There are a variety of sizes from postage stamp-sized to large cookie and chip tins. The metal is quite thin, so drill with caution or use a punch to avoid tearing the metal. People have come up with all kinds of projects for candy tins, such as this Instructables collection.

Not only candy tins are pressed into ham service. Even tuna fish cans get into the act, like the legendary “Tuna-Tin 2” 40 meter transmitter. You can read all about this Doug DeMaw, W1CER, creation from 1976 at DIYRadio. Cans make great sub-enclosures in larger projects, too.

Hobbies and Crafts

Finally, hobby, outdoor, and craft stores sell a wide variety of containers and boxes that can be used for electronics. Metal toolboxes make very nice enclosures for electronics, particularly portable or mobile radios, and can even serve as a ground plane for a mag-mount whip! They are often lockable as a bonus. Larger coolers can carry an entire station, may have wheels, and are almost always water-resistant.

My VHF/UHF emergency communications station in the photo below was built in one such cooler. Watch for seasonal sales at the start of camping, fishing, hunting, and boating seasons.

Although they aren’t often used for projects, tackle boxes, compartmented trays, and storage boxes come in very handy.

These can be used to keep connectors, parts, and hardware organized and ready for action in the field. I save my chewing gum and peanut butter jars to make great hardware kits, even including a crimping tool with the terminals so everything is kept together and sorted.

The Eye of the Beholder

I hope this article gives you the idea that useful materials are all around—not only for enclosures, but for hardware and accessories, too. Using inexpensive materials lowers the “barrier to entry” for building your own gear and will make you a more capable and flexible homebrewer.

Editor’s note: For those less inclined to homebrew enclosures, you’ll find the DX Engineering Utility Enclosure Kit at DXEngineering.com. Check out this article on ways customers have put the DXE-UE-2P Utility Enclosure to work around their stations.

The post Ham Radio Tech: Inexpensive Project Enclosures appeared first on OnAllBands.

This is the second installment of a two-part article about RF when you are operating “in the field,” meaning away from a fixed station.

For example, when you are operating a portable station for Parks On The Air (POTA), that’s considered “in the field” whether you are in an actual field or a parking lot or not even outside. Field Day certainly qualifies in most cases. In both parts of this article, the RF from your transmitted signal is what we’re concerned with.

Mechanical Concerns

We can start with some non-RF considerations that are certainly related to antennas, but not the radiated RF.

Most antennas used in the field are either ground-mounted or lower in height than at a fixed station. This, combined with the likelihood of their being in a public space, presents a variety of hazards to passers-by and other visitors. Your goal is to keep people from walking into, tripping over, touching, or otherwise getting too close to the antennas and feed lines.

The photo below shows a typical portable station with a table, tarp, and temporary antenna about 20 feet away in the background.

You can see the yellow rope placed around the antenna as a warning not to get too close. Plastic fence posts were used to hold the rope. Yellow caution tape is inexpensive and even more visible. Remember that many parks prohibit sticking anything in the ground, even for safety. In such cases, orange traffic cones are a good compromise.

Feed lines and power cords present a tripping hazard to both visitors and operators. If allowed, a stake in the ground next to the cables with a bit of yellow caution tape marks their location and can secure the cables. I always tie or secure the cables to a table leg so that if something does happen, the equipment is not dragged off onto the ground. (Don’t ask me how I learned to do this…)

Finally, don’t install your antenna where it can come in contact with vegetation. The end of an antenna element can present fairly high RF voltages, even at 100 watts output. This is enough to heat up leaves to the point where they will catch fire or at least smolder. Starting a fire is a definite no-no! (Don’t ask me how I learned this, either…)

Choose Your Words Carefully

Before we go any further, I need to remind you that the word “radiation” when referring to our transmitted RF may be accurate, but it is not a word the public or facility staff are comfortable with. I am careful to keep things simple and speak of “radio signals” instead of “field strength” or “radiation.” If someone asks about risks, you could truthfully tell them they might get a slight shock if they touch the antenna while you are transmitting. (If you are using an amplifier, it might be harsher than “slight,” so consider the possibilities.) Then explain that is why you have taken steps to prevent anyone from accidentally coming in contact with the antenna.

This is also a reminder to read or re-read the paragraph on preventing RF burns in the first part of this article, “RF Management—In the Field.”

RF Field Strength

The primary concern of this article is the high RF field strength near an antenna. FCC rules require us to evaluate the RF exposure from our fixed station antennas. Portable stations don’t require the same level of scrutiny, but you can use the same methods to determine whether your portable antennas might present a hazard to you or the public with respect to the Maximum Permissible Exposure (MPE).

Uncontrolled vs. Controlled

The allowed exposure levels are different for two kinds of environments—controlled (or operational) and uncontrolled (or general public). For a fixed station at our home, for example, the antennas are on private property and access to them is limited by property boundaries, fences, etc. This implies that anyone in the vicinity of the antenna either knows it is present or is there with your permission and supervision.

This is a controlled environment, and the MPE levels are higher because it is assumed the person can either take steps to stay away from the antenna or avoid being close to the antenna when the station is transmitting.

Uncontrolled environments are different and assume someone near the antenna is not aware of what it is or that it is present. They may approach the antenna at any time and are not assumed to be under your supervision, nor can they manage their own exposure.

For example, a vehicle-mounted antenna on your car in a parking lot can be approached by anyone in the lot. This is why the MPE levels are lower for uncontrolled environments. It’s safest that you assume these limits apply when considering how to construct and use your station.

High-Q Antennas

Another factor to consider is how your antenna radiates a signal and whether the RF field strength near the antenna will be particularly strong. The antenna’s ratio of stored energy to radiated energy is a measure of the antenna’s Q. Q is also known as quality factor, and for components, measures the ratio of reactance which stores energy to resistance which dissipates energy.

Antennas that store a lot of energy in the near field (within a wavelength or two of the signal frequency) can build up a surprisingly high field strength for any given power. These are known as high-Q antennas.

A high-Q antenna usually has a very low radiation resistance, which represents the antenna’s ability to radiate power into its far field, which is what launches our signals. The low radiation resistance means the antenna has to store a lot of energy for our transmitter output power to be turned into radiated signal (or heating in antenna system losses).

Imagine our antenna as a balloon being inflated by a compressor that delivers a continuous flow of air—this is our transmitter. The antenna’s radiation resistance is represented by a hole in the balloon through which air leaks out to the outside world (i.e., our transmitted signal). The balloon inflates until the amount of air leaking through hole balances the compressor’s output. The smaller the hole (the lower the radiation resistance), the higher the pressure in the balloon must be (the near field strength) for the leaking air to equal the incoming air.

The relationship between stored energy and radiated power and Q is clearly presented in a February 2013 QST article, “Q and the Energy Stored Around Antennas,” by Kai Siwiak, KE4PT. In the article, he describes and illustrates these important relationships and gives examples for real-world antennas.

For example, dipole antennas have a Q ranging from around 7 to 20, while small HF transmitting loops (a.k.a., a “magnetic” loop) can have a Q as high as 1,000. Antennas that are physically small compared to the transmitted signal wavelength generally have low radiation resistances and are high-Q. 

You can tell if you have a high-Q antenna if the SWR bandwidth of the antenna is low compared to a full-size antenna. Along with the small loops, this includes popular antennas like loaded whips that are often mounted near the ground.

Tune the antenna for an SWR of 1:1 at the operating frequency. Then find the two frequencies at which SWR increases to 2.6, F_U and F_L. Divide the square root of F_U x F_L by the SWR bandwidth, F_U – F_L, and that will give you Q.

For example, if SWR equals 2.6 at 14.275 and 14.295 MHz, Q = 714. That’s a high-Q antenna!

Bear in mind that losses in the feed line will make SWR look a little better at the meter than it is at the antenna terminals, so the actual SWR bandwidth is smaller and Q is higher.

How Safe is Safe?

Like most questions about antenna systems, the answer always seems to begin with “It depends…” So do answers about minimum safe distances for transmitting antennas.

The answer depends on operating frequency, antenna Q, and transmitter output power. Since every portable setup is a little (or a lot) different, you can’t be modeling or making complex calculations all the time.

To help amateurs deal with this complexity, the ARRL provides an online RF exposure calculator.

The following is a calculation for a 100-watt, 14 MHz station using unprocessed SSB with a 20% operating duty cycle and a ground-plane antenna with 1 dBi of gain.

Note that it’s safe to get pretty close to the antenna. However, if I turn on speech processing or operate more aggressively, such as during a contest or POTA activation, the minimum distance will increase. Similarly, using a mode like FT8, which has a 50% duty cycle of full power on periods, will increase minimum distances still further.

This short table is an excerpt from Table 5.7 of RF Exposure and You (see this article’s conclusion for how to obtain that book) that provides typical gains for some popular portable antennas. For a vertical dipole or end-fed half-wave antenna, use the half-wavelength dipole gain. For a “hex” beam, use the two-element Yagi gain. Loaded whips are less efficient than a full-size vertical, so that antenna’s safe distances are a conservative estimate for the whip.

Typical Antenna Gains in Free Space (dBi)

• Quarter-wave ground plane – 1.0
• Half-wavelength dipole – 2.15
• 2-element Yagi – 6.0

For the special case of a small HF transmitting loop, the minimum distances are larger, due to the higher stored energy of this very high-Q antenna. Siwiak calculates these minimum safe distances in his May 2017 QST Technical Correspondence item, “RF Exposure Compliance Distances for Transmitting Loops, and Transmitting Loop Current.” 

From that article, for a one-meter-diameter loop with five watts of continuous transmit power on the 40–10 meter bands, the minimum safe distance for the uncontrolled environment is 1.7 meters (5.6 feet). This increases to 2.1 meters (6.9 feet) at 10 watts output power. Table 17 from the FCC OET Bulletin 65B shows the safe uncontrolled distances for 150 watts increasing from 2.8 meters (9.2 feet) on the 40 meter band to 4.2 meters (13.8 feet) on 10 meters. 

Using an amplifier, such as for a special event or contest, with a small loop increases the minimum distances on 40 through 10 meters to 17.4 feet to 42.4 feet, respectively. (A two-meter-diameter loop on 80 meters requires 21.6 feet of separation at full power.) 

See Siwiak’s March 2012 QST Technical Correspondence article, “An Antenna Idea for Antenna-Restricted Communities” for more information.

Please Think About RF Safety

It’s easy to overlook these concerns in the “heat of battle” when you are just trying to get a station put together and on the air. Hopefully, this article will encourage you to consider antenna placement in the field. I see far too many pictures of portable setups where the antenna is a few feet away from a 100-watt transceiver. There are even photos of “mag loops” sitting right on a picnic table next to the operator! Don’t do that.

You can learn a lot more on the ARRL’s RF Exposure website. The excellent text reference RF Exposure and You by the ARRL’s Ed Hare, W1RFI, is downloadable at no cost as a PDF book. It has many helpful tables and examples.

I don’t think RF exposure is something we should be afraid of, but neither should we be careless in how we treat it.

The post Ham Radio Tech: RF Safety—In the Field appeared first on OnAllBands.

This is the first of a two-part article about RF when you are operating “in the field,” meaning away from a fixed station.

For example, when you are operating a portable station for Parks On The Air (POTA), that’s considered “in the field” whether you are in an actual field or a parking lot or not even outside. Field Day certainly qualifies in most cases.

Because these are temporary situations, you have to apply a different set of techniques to get everything working and keep it working.

“RF Management”–What Does That Mean?

In both parts of this article, I’ll consider the RF to be from your transmitted signal. There is certainly RF floating around from other signals, and some might be very strong, but let’s deal with your transmitted signal here.

What does the “management” part mean, though?

I have been using the term to include all of the various techniques that are used to keep our RF where it belongs and out of where it doesn’t belong. That includes configuring your station so that it performs correctly when you are transmitting. So, we are going “manage” how your station performs when the strong RF is present.

As you’ll see, that covers a surprisingly wide range of concerns.

Where Is the RF? 

Better to ask, Where isn’t the RF? That is really a better question than the first part.

We tend to think of our station as “over here” and the antenna radiating RF as “over there,” so the RF just flies away in the direction of other stations. Well, not quite. You, the operator, and your station are very, very close to where that strong RF is launched, at least electrically.

Let’s ask a question: What is the wavelength of a 40 meter signal?

Not a trick question! It’s about 40 meters, which is about 132 feet. More specifically, a 7.15 MHz signal has a wavelength of about 42 meters, which is about 137 feet.

Note that only two of the HF bands contain the wavelength by which they’re known: 160 meters at 1.875 MHz and 80 meters at 3.75 MHz.

If your 40 meter antenna is closer to you than about 1/2 wavelength, or 60-something feet, you’re right in the near field of the antenna! It takes another 100 feet or more to get you out of the strong RF field.

The resulting strength of your signal is going to be STRONG!

As a result, RF is going to be picked up by just about every bit of conductive material within 100 feet or more of the antenna. Pro tip—you are conductive as well.

Everything in your station—everything—is going to have RF voltage and RF current on it. Unless you are operating in a metal shipping container, you might as well figure out how to deal with RF.

Let’s start with your station equipment.

RF and the Equipment Table—Bonding

Take a look at your typical portable setup. There will be a radio, power supply, maybe an antenna tuner, a laptop or tablet for logging and digital modes, headphones or other audio gear, and a gadget or two. All of these are connected together with short antennas…er…wires and cables.

If you just throw everything on the table and hook it all up, there are lots of paths for RF to follow. Some might be low impedance so the RF current is high, and some might be high impedance so the RF voltage is high. The end of any unconnected wire or cable will be a high impedance point and that’s where you get an “RF burn”—on microphones, keys, and isolated metal boxes. You never forget an RF burn on your lips from touching a “hot” metal microphone!

These aren’t particularly hazardous, but they are obnoxious!

Even more obnoxious is equipment misbehaving when you press the key or mike switch. Maybe an automatic tuner decides to suddenly re-tune, a computer keyboard freezes up, or a radio changes a setting. This is caused by RF current getting into (or out of) something it shouldn’t. And what causes RF current to flow? RF voltage! More specifically, a difference of RF voltage between pieces of equipment.

If you can minimize the difference in voltage between pieces of equipment, you will also minimize RF current flowing between them along connecting cables.

That’s what bonding does for you.

If you look up “bonding” in an electrical dictionary, you’ll find that it is “a connection between two points to keep them at the same potential or voltage.” That’s all—no fancy implications or calculations. You just want to keep everything on the equipment table at the same voltage, and you do that by bonding them together with heavy wires or straps. The wires and straps should be short so they don’t have an appreciable impedance of their own.

In a portable setup, the easiest way to bond everything is to connect all of the equipment directly together. Have an assortment of jumper wires (#12-16 is good) or straps (flat tinned braid works well) that connect to screws on the metal enclosures. Powerpole connectors on the wires allow the equipment to be bonded however you arrange it. I recommend using green wire insulation and connector bodies, signifying a ground connection.

Another option is to put some aluminum foil under all the equipment and connect the enclosures to it with heavy test clip leads (#18 or heavier). The metal surface helps equalize voltage.

This is a great addition to any go-kit and has saved Field Day for me more than once.

The foil weighs hardly anything, so you can even use it for Summits On The Air (SOTA) stations carried in your pack. When you’re done, wad it up and recycle it. The foil surface should be big enough to cover a strip under all your equipment. I find a three-to-four-foot strip is more than adequate.

RF and the Station Wiring

What about all those cables connecting everything together? There are three basic techniques that will reduce or eliminate most RF problems:

1. Use the shortest cables you can. One-foot USB and audio cables are available. 
2. Coil up excess cable in a figure-8 to minimize its inductance and the RF voltage it will pick up.
3. Use shielded cables for everything and avoid plastic, unshielded boxes for equipment enclosures.
4. Have Type/Mix 31 (preferred) or 43 ferrite clamp-on cores available.

What is a figure-8 winding? This is a handy technique for all kinds of cable, including coax feed lines, power cables, and extension cords. The basic idea is illustrated in the last half of this YouTube video on cable winding for video work. If you practice these techniques, you’ll avoid creating a spiral twist that creates kinks. For small cables, you can wind the figure-8, then fold the two halves together. Winding half the turns in opposite directions causes a magnetic field to create equal-but-opposite voltages in the coil, minimizing RF pickup.

If you use the aluminum foil approach or have a metal table, lay the cables, including the excess length all coiled up, on the foil. That minimizes the length of cable exposed to the RF fields.

If you do need the ferrite cores, place them on the affected cable as close to the equipment experiencing interference as possible. Wind several turns of the cable onto the core before snapping it shut. Be sure both surfaces of the core are flat against each other. This creates an impedance that blocks the RF current where it is getting into the equipment.

If you’re not sure what mix makes up a “mystery core,” it’s worth buying a half dozen, then labeling or color coding them as in this photo of a ferrite core kit. The toroids can be used to wind multiple turns of coax and power cords. Snap-ons can be labeled with a permanent marker or colored tape.

A combination approach that accomplishes bonding and keeps all of your equipment together is a portable rack. These have metal shelves and rails with an overall plastic enclosure. They’re usually available as portable audio equipment racks.

You can install all of your portable equipment more or less permanently in one of these racks. This lets you bond everything, use short cables, and debug all of the wiring so that when you take the rack of gear to the field, you know it will work with a minimum amount of setup.

True, a rack is heavier and not suitable for backpacking, but for many portable vehicle-based scenarios, it will be just fine.

These photos are from my Field Day operation in 2023 showing an IC-7000 and an FT-7900 in a standard portable audio rack. All of the equipment is bonded to the metal rack shelf. The operating table is my great-Aunt Ruth’s!

Despite your best efforts—and every field setup is different—you may find that transmitting on a particular band “lights up” the station equipment (or the operator). You might see RF interference to equipment, or a “hot spot” may cause a tingle (or more!) on some frequencies.

In this case, use a 1/4-wavelength piece of wire (calculate as 470/f in MHz–length is not critical) attached to the affected equipment on one end with an alligator clip and left open on the other. Insulate the open end.

This detuning wire will create a low-impedance point, lowering RF voltage where the wire is attached. The open end may have high voltages on it, so insulate it and don’t put it where you might touch it or step on it with bare feet! (Don’t ask me how I learned this…) Have one detuning wire for each band you plan on using.

RF on the Antenna System

Other than on the antennas themselves, as discussed earlier, RF is going to be picked up by every conductor in your station, including by the antenna feed lines as common-mode current. This is a particular challenge in mobile operation since the vehicle body is part of the antenna. The RF picked up by the feed line will flow into your station and cause problems unless you take steps to block it:

1. Use a common-mode choke (ferrite or wound-coax) where the feed line attaches to station equipment.
2. Add one or more chokes along the feed line between the station and antenna. If you are using an end-fed half-wave (EFHW) antenna, a choke at the impedance transformer may affect the antenna’s SWR. Check the antenna manual for guidance.
3. If you are using a vertical antenna, such as a whip with a base-loading coil close to the ground, place some chicken wire or hardware cloth under the antenna to act as a ground plane. Route the feed line underneath it to maximize the shielding effect.
4. If your antenna is mounted on a vehicle, bond the antenna mount to the body with a heavy wire as close to the mount as possible. This helps keep the feed line from becoming part of the antenna.
5. In a vehicle, operate with the doors closed to keep RF on the outer surfaces. A ferrite choke where a feed line enters the vehicle is also helpful.

Finally, what about a ground connection to the Earth itself?

Generally, you don’t need one! Most generators do not require a ground rod or connection—check the manual.

A vertical antenna will require radials or a ground screen as in item three above but does not need a direct connection to the soil. Horizontally polarized antennas like dipoles, most EFHWs, and double-whips will be de-tuned by a ground connection. In many public places, it is not allowed to drive stakes or rods into the ground.

What about lightning protection?

In a portable or mobile setup, the best advice during storms is to lower the antennas to the ground, disconnect the feed line and secure it at least six feet from the station. There is little you can do to protect your equipment from a lightning strike in the field. Take shelter yourself! If you’re in a vehicle and lightning is striking nearby, close the doors and try not to touch any metal until the storm passes.

***

This article touched on some of the important aspects of dealing with the strong RF you’ll encounter when operating a portable station. In the next article, I’ll discuss some concerns for RF safety in these setups, an often-overlooked aspect of setting up away from home.

The post Ham Radio Tech: RF Management–In the Field appeared first on OnAllBands.

For Guglielmo Marconi, the great challenge was to transmit wireless signals across the Atlantic and to all the ships at sea. He built stations at Poldhu, England; Glace Bay, Nova Scotia; and Cape Cod, United States—all near the ocean.

Was this done with a knowledge of oceanside propagation, or was it because he was in the business of ship-to-shore communication?

Those of us blessed with a waterfront residence on the east or west coast have much stronger communications links across the Atlantic or the Pacific than people living in the middle of the continent. We’ve all heard stories of antenna farms on or near saltwater marshes that get much improved signals. I even heard one about a ham with both feet in the Atlantic operating a low-power backpack radio with a whip and having a QSO with a station in France.

The “saltwater amplifier” is the increased ground conductivity near the sea, leading to more antenna gain. Average soil has a conductivity of 0.005 Siemens per meter, saltwater averages 5.0 Siemens per meter—an improvement by a factor of 1,000.

Do the math and that’s roughly 10 dB of gain. Imagine turning your 10-watt QRP radio into the equivalent of 100 watts.

Medium Wave Beside the Waves

Early on, some AM stations in the metro New York City area learned that oceanside towers can produce big signals. For more than four decades, High Island had been home to two of the biggest New York City AM signals: WFAN (formerly WNBC) on 660 kHz and WCBS on 880 kHz.

CBS’s station was so powerful that it could be heard as far away as Florida and Chicago on good days. Typical coverage included daytime signals up the coast as far as Cape Cod and down to Cape May. Then as now, CBS was one of America’s principal broadcasters, and the company found the saltwater ground system of Long Island Sound ideal for carrying radio waves.

Broadcasters have sometimes found some advantage or necessity to locate transmitter sites on islands. These islands vary from the isolated home of KUHB on St. Paul Island in the Bering Sea to the now defunct WMBL on “Radio Island” near Morehead City, North Carolina. It was the first radio station serving the area and was well known for its clear reception and surprisingly long range.

Gordo’s Ground Shootout

Gordon West, WB6NOA, once did a head-to-head comparison between a traditional copper-foil strip that went nearly all the way around his boat and a seawater ground. The results of his experiment were published in Sail Magazine. Using an Icom marine SSB/ham transceiver and Icom AT-130, he was careful to retune the antenna each time ground systems were switched for an accurate comparison.

While the copper foil capacitive ground did produce a usable signal, the seawater ground improved antenna power output considerably.

In addition, this configuration decreased the noise floor while receiving and increased sky wave signal strength. It also caused a four-foot fluorescent tube to glow brightly with modulation peaks.

He saw the light.

WSPR Test

Greg Lane, N4KGL, did a test comparing two identical verticals, one on the beach near the water and another inland, away from the beach. In addition, a low dipole was added to the mix to see if horizontal polarization made any significant difference. Only simultaneous spots were used for comparison.

Using a pair of identical WSPRlite transmitters on 20 meters, Lane first established a baseline with a WSPRlite attached to each vertical. Both were set up several hundred feet inland at the same distance from the ocean. Evaluating the 55 spots, all were similar in output and operation. Using a low-power wattmeter onsite showed no discernable difference in output.

Two trials were conducted with the saltwater vs. land antenna comparison. The first one had the antenna placed at the shore and the other 700 feet inland. The second trial had them placed 200 feet apart. Results showed the saltwater vertical always beat the inland vertical for any WSPR spot with an average 10.8 dB advantage. As expected, the closer the antenna to the water, the better the gain.

In the low dipole vs. saltwater vertical scenario, the saltwater vertical was better 32 times out of 33 spots, with nearly a 10 dB advantage. The only downside was higher radiation angles.

Overall, his observations appear to support the presence of a significant saltwater gain.

Radial Placement for Maximum Gain

The object of the saltwater effect is to improve the ground system for better efficiency. Rudy Severns, N6LF, reminds us when AC current (RF) flows in a conductor, the current tends to flow only near the surface. The ground current for a saltwater vertical antenna is restricted to a thin layer near the water surface (skin depth). This means radials need to be near the surface to take full advantage of the saltwater effect.  

Running a copper wire with a fishing weight (or several) to the edge of the surf would probably be sufficient for casual use at the beach. A floating radial on an anchored pool noodle would be a good solution in calm inlets and tidal pools.

Tides are a challenge. Local tides can range from a foot to more than 50 feet. That would significantly cover the radials and vertical element, changing the effective length of the antenna system. A workable long-term solution could be a floating dock or a float substantial enough to support the antenna. You don’t need a long radial—attaching a piece of sheet metal or screen several feet long to the bottom or side of the dock can provide a low-resistance ground without a trailing wire.

Several DXpeditions have used pairs of 1/4 wavelength elevated radials connected to vertical antennas directly over flooded reefs. The radials need to be kept well above the water surface, even at high tides, for best results.

Close Also Counts

The objective with a vertical monopole antenna is not just to have any ground connection, but to have a low-loss ground plane under the base of the antenna. Think of the ocean like a huge copper sheet, just not quite as conductive. Being within a few wavelengths of an ocean is the next best thing to having radials near or in the water. Walt, K4OGO, has some videos online that discuss antenna designs and setup for use on the beach.

Going mobile? When you park close to the sea, the radio waves go over the surface, reflect and bounce off into the atmosphere and skip, just like stones or pebbles across a pond.

Reflections on Saltwater Propagation

Seawater is too good of a conductor to pass radio waves—instead, it reflects them like a mirror off of its surface. Saltwater contains Na+ and Cl- ions. Saltwater is electrically conductive because these ions are free to move in solution.

You might argue that 10 dB is only a little more than 1.5 S-units, but it can mean the difference between “can’t hear a thing” and full copy.

This might be a good time to book that beach vacation to fish for some DX!

The post The Saltwater Amplifier Effect (& How it Impacts Your Amateur Radio Station Performance) appeared first on OnAllBands.

Did you know that the Federal Communications Commission (FCC) now requires all amateur radio stations in the U.S. and possessions to be evaluated for RF exposure? It’s been a little more than a year since this went into effect, so OnAllBands thought it would be a good time to remind our readers.

As of May 3, 2023 (the end of a two-year transition period), all transmitters operating in the U.S. were expected to comply with the exposure rules. The new rules did not change exposure limits, but those who were previously exempt from running exposure calculations now must comply.

Under the old rules, many amateurs were exempt from the need to do an evaluation—based on transmitter power used with each band, for example. Under the new rules, there are no longer any service-specific exemptions. These have been replaced with formulas that can be used to determine whether an installation needs to be evaluated.

The ARRL noted that these formulas can be used for exposure that is beyond the near-field/far-field boundary of your antenna, defined as wavelength/2π or 0.16 wavelength. Most stations that were exempt under the old rules will still be exempt from needing to perform a more complete evaluation under the new rules.

As OnAllBands reported last year:

“Under the updated FCC rules, every radio amateur is responsible for determining that their station does not cause exposure that exceeds the FCC MPE (Maximum Permissible Exposure) limits to any person, either within their homes or outside of them. This is also required for portable and mobile operations.”

Gregory Lapin, N9GL, QST Magazine, May 2023

Lapin noted that the FCC does not require that the results of a station’s exposure analysis be submitted, but “it is advisable to keep a record of the analysis so that if there’s ever an exposure complaint about that station, the calculations can be shown to the FCC.”

You can read N9GL’s entire QST article here.

There are many resources on the internet for calculating this RF exposure. The ARRL’s website includes an RF Exposure Calculator (below) to assist amateurs in performing station assessments.

The ARRL points out three ways to evaluate your station: calculations (using the above calculator, for example); antenna modeling; and measurements using calibrated equipment. You’ll find many more details about these methods and additional information in the ARRL document, Frequently Asked Questions about the FCC RF Exposure Rule Changes

We also highly suggest reading these resources recommended by the ARRL:

• 100th Edition ARRL Handbook’s RF Safety Section
• Helping Amateurs Interact with Neighbors Asking about Radio Transmissions 
• ARRL Learning Network Video on RF Exposure 

Also check out these FCC resources on RF exposure

• FCC Frequently Asked RF Exposure Questions
• FCC Radio Frequency Safety
• FCC Q & A about Biological Effects and Potential Hazards of Radio Frequency Electromagnetic Fields

Questions? Share them in the comments below or email me at KE8FMJ@gmail.com.

The post Get up to Speed on Amateur Radio RF Exposure Rules appeared first on OnAllBands.

Power. It is one of the most important aspects of running an operation. But what if you don’t have access to AC power or a storm knocks out all power in your area?  

What Are Your Backup Power Options?

There are some differences if you are at home or in the field. At home you will want to power more than just a radio and its accessories—things like a refrigerator, air conditioning, and internet service.

What you want is an uninterruptable power supply (UPS). These can be as little or as large as you can afford. Most of us have small units connected to our computers for safe shutdown. There are room size UPS units that back up large data centers, hospitals, and other critical infrastructure.

The big question is how much runtime do you get? This is almost solely dependent on…

…you guessed it. Batteries.

Lead-acid batteries, most often deep-cycle, are a good choice for emergency power. They are rugged and have relatively low energy density. The deep-cycle option also handles a slow discharge well. They can be used with or without a battery box. A battery box can be purchased or homemade. The cost is on the lower side for batteries as well. The main disadvantage is that they can be extremely heavy, which is usually not an issue for home use.

The next option for home use is a generator, like the Generac GP3600 Series Portable Generator shown below. These can provide power for an extended time period and are rugged. However, generators are bulky and not easy to move. You also need to have fuel to power them and keep them running smoothly.

Solar is a good choice for home and portable use. It also has the advantage of being environmentally friendly. A solar cell, or photovoltaic cell (PV), is a device that converts light into electric current using the photovoltaic effect. Multiple solar cells are connected inside modules and modules are wired together to form arrays. The arrays are then tied to an inverter, which produces power at the desired voltage.

A large array for maximum power can become very expensive. Home solar systems often have a way to store excess energy and feed it back into the power grid. Portable solar panels come in many shapes and sizes that you can roll up, fold up, or fold over for easy storage. Straight panels that are more rigid are a good option as well.

You’ll find several solar power options at DXEngineering.com, including Bioenno Power foldable solar panels and solar charge controllers, and the Samlex Solar Portable and Foldable Solar Battery Charging Kit below.

So, what are some good options for people out on a field exercise or during a Parks on the Air activation?

A choice that is growing in popularity is a power station, like the A-iPower 300W Lithium Portable Power Station below. It includes outlets for USB and 12-volt power, with receptacle plugs for easy hookup and power supply. While power stations are relatively lightweight, they may not be the best option for tossing into a backpack from a weight perspective.

Another extremely popular option is the lithium iron phosphate battery. Lithium iron phosphate (LFP) is an inorganic compound with the formula LiFePO4. Some of its advantages include long cycle lifetimes, high power density, wide operating temperature range, and easy transportability due to its light weight. You can find a range of Bioenno Power LiFePO4 12VDC batteries (see the 12 Ah model below) and battery/charger combos at DXEngineering.com.

What is your favorite alternative or backup power? Questions?

Share them in the comments below or email me at KE8FMJ@gmail.com.

The post Backup Power for Home & Field appeared first on OnAllBands.