40m Mastless NVIS Antenna
Even though I had a working mostly homebrew station, I now realize I had only a small idea what I was doing, and almost no understanding of what made antennas work. No mast in this context means no structure taller than a person. Crossing of Beverages has little effect if they are not parallel or nearly parallel. Here is concept antenna you may find worth trying. The tuning range will vary if the size is changed.
Active 3-30 MHz Hula-Loop Antenna for Shortwave
Lower value chokes can be used, but at some point, the low frequency response will suffer. When this type of insulator is mounted horizontally, the wire's weight will stress both the molded nail tube and a single tab. The antenna is simply hung from a hook or string and the end could be pulled into the air by tossing a string over the branch of a tree. Even with the Q-killing 4. With the values shown the buffer will work well from below kHz to about 15 MHz which covers the frequency range where an antenna buffer is useful.
Kohler demonstrated how easy it was to reach false conclusions, unless we use valid measurements. Most antenna myths and misconceptions, many making it into print in articles, come from repeating feelings or unsubstantiated claims, or are based on improper measurements or models.
I've seen comparisons years apart, going on memory of how signals were on some other antenna that was long gone! I presently have a great deal of room, with wiring in place to install multiple antennas, and reasonably good test equipment.
This allows installation of multiple antenna systems at the same time, which allows direct comparisons over time, as well as measurements. I constantly refine antenna systems by comparing systems against each other for extended periods of time, usually more than a year. Even though I use engineering tools books and models , I always compare and measure actual working systems in multiple ways if possible. My station has a convenient switching system, allowing instant comparison of antenna systems.
When an antenna system is almost never better, or evolves to almost never being used because other system is better, I abandon that system. I keep the better-working systems, and try to find something better still. I presently have over thirty Beverages in three different clusters of arrays, the end result refined through years of measurements and A-B comparison testing of systems.
User interface is important when comparing antennas. Since the early 's, I've used push-button antenna controls. Push-button controls are good for contesting, and good for experimenting. This control panel selects antennas for each receiver in the K3. The far left switch is for the main receiver which goes to the left ear, and the next switch left goes to the sub receiver which is the right ear.
I have seven primary antenna group selections available. The K3 is the only standard transceiver system offering true diversity. Other receivers advertise diversity reception , but performance is poor. As a general rule, the receivers are not identical, and audio phase is not locked! To have true stereo diversity, each channel must have an identical, or nearly identical, receiver. All frequency control and bandwidth adjustments must track.
The small, silver, push-button box on the desk selects directions. In the normal case, I lock all antenna group directions to one box. For contest use, directional control of antenna groups can be independent, through use of multiple identical control boxes. My system has a special locked-position for Europe antennas, since they are the most frequently used antennas. Operators can lock their "ear of choice" to Europe, while scanning any of eight directions on the other ear, using the push-button directional control.
I occasionally hear or read claims that insulation prevents charged droplets of water from making an antenna "noisy". I've never been able to verify that claim, either in A-B tests of actual antennas, or through planned experiments. Other reports, many from reliable sources, also seem to discredit the claim that charged droplets striking the wire cause noise.
One of my experiments was to charge a stream of water against earth with an extremely high voltage supply, and spray the charged water on a wire. Other than corona noise from sharp points, the type of wire bare or insulated made no difference at all in "noise". The charged water droplets were not discharging into the wire like hundreds of random charged capacitors, they generated no detectable noise at all.
This is really what we would expect, if we consider that each drop contains only a very miniscule amount of charge, and also has nearly perfect insulation distilled water is a very good insulator.
Controlled and general observations support the idea that corona actually cause precipitation static , rather than charged individual droplets striking the antenna. In Ohio, my long Beverages stretched across open farm fields. Snow would whip across the fields, rain would pelt the wires, yet insulated wire and bare wire Beverages, running in the same direction, always had about the same noise level.
Beverages that picked-up corona or "p-static" noise were always near or aimed at tall towers. With corona noises sizzling at over-nine on my tall towers, Beverages and even small "magnetic" loop antennas aimed at my towers or near my towers would "hear" the same precipitation noise. The same was true for tower-mounted antennas. The largest noise problems came from antennas mounted high on towers, and generally were with antennas that had "sharp" ends jutting out in the air.
Lower antennas, even those of identical construction, were either significantly quieter or totally free of precipitation static. This effect was reported many times by contest operators and DX'ers with stacked antennas. They universally switch to low antennas to eliminate or reduce p-static, even though the same moisture is hitting the lower and upper antennas.
This strongly indicates precipitation static is from corona discharge, and not from charges in each individual drop of moisture hitting the antenna. After my move to Barnesville, Georgia, hook-up wire was pressed into service in my first group of temporary Beverages.
As non-insulated conductors in more permanent antennas were added, there wasn't any observable change in inclement weather noise. As before, antennas nearest or aimed at my tall towers picked up p-static noise.
Antennas located away from the towers remained free of precipitation static. Each was true, whether bare or insulated wire was used. There is often some element of fact behind rumors. Insulated wire may reduce noise, if the insulation reduces corona discharge.
Insulation can prevent St. Elmo's fire from narrow points. Also, insulated wire might result in more consistent performance. If a substantial part of the conductor is in contact with unwanted resistive paths, such as wet brush or tree branches, insulation can reduce leakage losses and attenuation.
But we are probably better off just trimming back any substantial foliage in contact with the antenna wire, and using air insulation. In my experience, directly comparing various receiving antennas at the same time over many years, insulated wire has no major performance advantage. It also has no significant disadvantage. Use insulated wire if readily available, but unless your antenna is in contact with soil or other conductors, don't go out of your way to purchase insulated wire.
Field telephone wire is sometimes used in reversible Beverage antennas. Such wire is generally a terrible choice. I measured a meter band loss of around 2 dB per feet with clean dry field wire, and around 4 dB loss per feet on 7 MHz. This means the transmission-line mode of a reversible full wavelength Beverage, which supplies the far end connection, would have a dry weather loss of about 10dB on meters.
Field wire, speaker wire, or zip cord has to be the ultimate in trading performance for cost. The most common Beverage wire types are single-conductor hook-up wire or electrical wire, electric fence wire, and specialized antenna wires such as copperweld. The only easily noticed differences between commonly-used wires are in physical properties, such as ease of soldering, strength, and life. I've generally avoided aluminum wire because of connection issues, so I cannot comment on aluminum Beverage wire.
Copper wire is a good choice if supports are close, and if it is readily available. Pure copper wire lacks the mechanical strength of steel-core wires, but is very easy to work with. It is softer, making it easier to bend. Copper wire can be repeatedly scraped, cleaned, and re-soldered without worries about piercing a thin copper coating and exposing a rust-sensitive steel core.
Copper wire is readily available, and relatively inexpensive, in large quantities. Like copper, it is easy to clean and solder after it has been exposed to the weather as long as you are very careful to not scrape through the outer layer of copper.
It is considerably more difficult to work with than normal pure copper wire, any small kink or sharp bend will substantially weaken the wire. Be mindful how thick copper is.
Many copperweld wires have such a think layer of copper that current flows in the underlying steel core on lower bands. Steel wires like electric fence wire are strong and cheap, but have some disadvantages. One disadvantage is rust. In middle Georgia, common brands of electric fence wire last about 5 years before rust becomes a problem.
If an antenna is properly terminated , contrary to some internet claims and rumors, there is no advantage to lossy steel wires, such as electric fence wire. This is because the wire self-terminates through series resistance distributed along the wire's length.
This effect can actually be measured and documented, by observing current taper along the wire. Due to the close proximity with lossy earth, Beverages have substantial current taper with distance. Current taper reduces available directivity, because antenna areas further from the feedpoint connect through significant attenuation.
This undesired current taper is increased with reduced height, as well as unnecessary antenna conductor losses. Most fence wire I've found is cadmium plated, rather than zinc galvanized.
Using RF current meters, zinc or cadmium plated steel wire clearly shows increased loss compared to copper or copperweld wire. At the same time beamwidth, and any advantage caused by increasing antenna length, must diminish. Steel fence wire would aggravate losses, and losses and spatial fading already limit performance of extremely long Beverage antennas. In a very long antenna, the small additional loss of steel fence wire would reduce performance. I use copperweld wire or electric fence wire, because strength is a primary concern.
With spans exceeding feet, my antennas need a large strength-to-weight ratio. Don't use welding wire! It is a very poor material choice.
Welding wire has poor conductivity, easily rusts, and as with aluminum, can be difficult to solder. There are claims non-metallic supports work better for Beverages, but there is not the slightest technical justification for using non-metallic support posts.
The only requirement for the support is it must hold the antenna up, and the support cannot connect the antenna to ground. A metal pole with a small PVC stub for an insulator is every bit as good as a non-metallic pole. Trees make good supports, especially if you use nail-type electric-fence insulators designed for wooden posts. PVC is wedged over the end of standard metal conduit. String may be required to hold the lower wire in the notch. Notice the wire floats freely through the insulator.
This allows a single tensioning point, and easy checking at one point to see if the antenna has lost tension from a break. I never anchor or wrap the Beverage wire around insulators, except at the ends. I always allow the wire to "float" through the insulators. The standard strain insulator hangs from a branch.
The beverage wire lays across the insulator webbing, fully floating. Only the hanging wire wraps the web. For end supports, I use trees, pressure treated lumber, or landscaping timbers. With a lot of tension, I backstay the poles to a dead-man generally an old brick buried in the ground. When I set end-posts with my power auger, I line the hole with copper flashing. The flashing becomes part or all of the feedpoint or termination ground connection.
When the wire floats along the length between ends, you can tension the entire antenna from either end. If anything breaks the wire, you can see it at any point! A "floating" wire is much easier to repair if it is damaged, because you only need release tension on one end to splice the wire. Re-tension that same end, and everything is restored. It takes no more tension to support a foot Beverage with supports every feet than it does to support a foot wire between two rigid supports, but it is a much more difficult to break the longer floating wire.
A longer "floating" wire will often take-up enough slack to remain up after deflecting a large tree branch, where a shorter rigidly-anchored span will almost certainly break either the insulators or wire. Some types of electric fence insulators will not last long. The unreliable types of post insulators have two square folds to hold the wire, a square shaped base, and nail through a small molded plastic angle.
The weak points of this insulator are the square retaining tabs, and the molded nail tube at the insulator base. When this type of insulator is mounted horizontally, the wire's weight will stress both the molded nail tube and a single tab. After three years, the few dozen installed here have virtually all failed. Round yellow or back plastic insulators with the nail going through the center, like the examples below, are much more reliable post insulators.
Ceramic post insulators may look great, but they do not allow floating the wire across the insulator. Even if you do manage to find a ceramic insulator that allows floating the wire, the ceramic will quickly wear away at the constantly moving wire. Tune for strongest signal, or strong increase in noise from the receiver. If you use a table model receiver or an amateur transceiver, make a single turn loop of about 18 insulated hookup wire by taping the wire in place one inch inside the foil loop.
Bring the wire away from the antenna on the middle of the side opposite the tuner. The pickup loop can be brought to the receiver by twisted pair or by RG or similar coaxial cable. Put the antenna on some insulating support so it can be tipped up on one side or corner. One of the early investigators working with us Cheryl Hagn pointed out that a pillow serves very well for this support! While listening to the interfering noise, tip the antenna a bit to reduce the noise.
Many times, with just a minute or so of adjusting, the noise from power lines, nearby TV sets, etc. I finish with a simple schematic diagram showing what you built. The newspaper and two foil flaps make a capacitor. The book allows you to vary the amount of overlap of foil, so you made a variable capacitor which is attached to the ends of a single turn loop, made of a very wide, flat conductor.
The receiver, sitting on the foil, has a good deal of capacity between its internal circuit board or chassis to one end of the loop. Its whip antenna is connected to the other end, so the voltage developed across the loop is injected into the receiver. Tuning the loop causes the voltage at one frequency to be maximized. This causes the increase in signal strength.
Noise from local sources — arcing power lines, fluorescent tubes, TV sets, etc — travels to your receiver along the ground. Its horizontally polarized components are attenuated very rapidly, so only its vertically polarized part gets through.
But skywave signals arrive at your receiver randomly polarized, so their horizontal part enters the antenna. HLA antennas can be made both larger and smaller, with foil that is wider or narrower. The tuning range will vary if the size is changed. If you decide to make a bigger HLA, just keep in mind that the total circumference of the outside edge of conductor should be kept to well under one-third wavelength.
Otherwise, the result will no longer be a small, horizontal loop above ground, but will have other maybe even interesting properties. Sheet aluminum, sheet steel, window screen wire but not fiberglass, which was the reason for my first failure to get one to work! She just put weights at the corners, and the capacity through the oxide layers was essentially a very good connection at RF frequencies.
The HLA was designed to cancel vertically polarized noise. To do so, it was engineered to be kept within about a tenth of a wavelength above ground — not elevated much at all. You can, of course, put them up much higher, but I offer no data on performance when the loop is elevated — other people can attest to the qualities of elevated, horizontal loop antennas. I hope you find this antenna interesting and useful. Some time ago, I had built one and was using it for reception on 15 meters, while using a grasswire for transmitting.
In contact with a ham in Europe, I noticed the lights blinking on and off slightly. The grasswire, being rather impervious to lightning, and the HLA cancelling QRN from the lightning, kept me from realizing that a storm was even in progress! Interesting article and thanks for uploading it!
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Imsges: antenna hookup
Customer Reviews 3yrs going strong - Review by: Multiple antennas actually may be the only case where a sloped feeder can make a difference, the slope will actually move the effective feedpoints further apart. If you inductors are significantly lower in resistance, add a series resistor to total around ohms.
Here's a little video showing it in action. There is nothing new or novel about reflector wires underneath horizontal dipoles with an example in shown in Fig.
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