Home made antennas - creative solutions for radio amateurs

Simple wire antennas which do not require special tools

Let's face it: Directional antennas with multiple elements and vertical radiators, possibly with trap circuits, magnetic antennas and the like, require advanced knowledge and experience in metalworking. Additionally an extensive range of tools and equipment might be required. Apart from a classic ground plane, a simple vertical radiator or an HB9CV for VHF, not much can be produced without a reasonably well-stocked toolbox. This is in stark contrast to DIY wire antennas.

Customized solutions without great expense

When building wire antennas, you should ask yourself what you want to achieve. Is it worth building a commercially available product yourself? An equivalent homemade wire antenna is certainly feasible, but it will hardly be significantly cheaper than a commercially manufactured product if you have high demands on manufacturing quality. The primary motivation for DIY is often the construction of antenna models that are not available in stores. Even if an individual solution is somewhat more expensive, it can sometimes be the only way to get on the air. Furthermore, the limited spatial conditions of a small property are a motivation for DIY an individual wire antenna. DIY wire antennas do not place too great a demand on the necessary tools and technical skills.

Materials, techniques and tips for long-lasting constructions

The following instructions are generally applicable to the self-construction of all wire antennas. Commercially available antenna wire for amateur radio consists of copper bronze wire or steel/stainless steel with clear PVC insulation. The copper bronze wire has a lower tensile strength than the steel wire, but is much more flexible and is easy to solder. Its tensile strength is sufficient for our purposes. The steel wire is designed for the tensile load of long wire antennas and consists of a few thicker strands, which makes the material quite unruly. In addition, there are high-quality antenna wires with a steel core and silver-plated copper braiding, as well as extremely weather- and UV-resistant insulation with Teflon-like properties. For initial test setups of relatively short wire antennas for the higher bands, a simple stranded wire with a cross-section of 1.5mm² is also suitable for the time being.

The strain relief loops on center and end insulators are included in the total length of the antenna when using insulated antenna wire. Bare antenna wire forms a short circuit at this point, so that only the simple length of the strain relief loop is included in the total length. Stainless steel box clamps are the first choice for fixing the antenna wire to the strain relief loops and to the end insulators. The nuts should always be tightened by hand first, and then the last turn should be tightened with an open-end wrench. Steel strands should always be cut with the pincer, but never with side cutter pliers. The latter will soon develop “caries”.

In the past, soldered connections on wire antennas were frowned upon and this view has persisted for a long time. In absolutely weatherproof connection housings, clamp and screw connections are justified. But imagine if you were to insert an uninsulated end of the standard PVC-insulated CU antenna strand into the shaft of a cable lug and simply crimp it. The strain relief provided by the plug shaft may be sufficient, but what happens behind it at the contact point with the CU strand, not to mention a galvanized steel strand? Corrosion and an imminent contact resistance are the inevitable result. The advice not to solder the antenna wire comes from the days of early broadcasting, when everyone had an L-antenna made of a rigid copper bronze strand hanging over the street or garden for their medium-wave radio. A directly soldered lead did not last long and broke at the soldering point due to the constant movement of the antenna. Therefore, twisting was always recommended at this point. If the connection point is fixed with strain relief, soldering and subsequent sealing with Zapon varnish or plastic spray is the better solution electrically. This method has proven itself. Solder joints treated in this way still look the same after a few years outdoors as they did on the first day. Always solder crimp or spade lugs first and then attach or screw them on. Otherwise the soldering point will not get hot enough due to the heat dissipation. The end of the antenna strand at the cable lug must be strain-relieved and immovably fixed. Finally, the soldering point is sealed with Zapon varnish or plastic spray. Always apply it only with a brush or mask the cable lug itself! Otherwise, the varnish will be absorbed between the contact surfaces, causing insulation! Heat-shrink tubing is also well suited for protecting the connection from the effects of the weather at this point. Insulating tape is not recommended; UV-resistant, black cable ties are a better alternative.

The monoband dipole

Calculating the length of a monoband dipole

The lengths given in the literature are based on calculations or are the results of experimental setups whose environmental influences cannot be reproduced. Length values calculated in advance are to be regarded as preliminary guide values. Here are two formulas for calculating the as-yet unabridged half-wave and quarter-wave lengths:

• Half-wave length (m): $\frac{{\mathrm{\lambda }}^{}}{2}=\frac{{150}^{}}{\mathrm{f\; (MHz)}}$
• Quarter-wave length (m): $\frac{{\mathrm{\lambda }}^{}}{4}=\frac{{75}^{}}{\mathrm{f\; (MHz)}}$

How to achieve perfect matching

Ideally, the goal of the final adjustment is to get the minimum of the standing wave ratio either in the middle of the band, for example on the border between the CW and SSB range, or in the middle of the band segment of your preferred mode. You cannot expect a homemade (or even a ready-made) dipole antenna to “work” right away. Most of the time, there is no way to avoid precise tuning. Depending on the installation height and other environmental influences, a velocity factor of 0.98 to 0.95 must be expected, by which the theoretically required length of the dipole must be shortened. Mount the dipole without shortening it for the time being and start measuring with an SWR meter, or better and easier still, with an SWR analyzer. Now you can shorten the dipole at both ends in small, equal steps and monitor the adjustment process via the SWR until you have achieved the best SWR in the desired band segment.

Guidelines for matching dipole antennas

Twin wire dipole: the versatile all-band radiator

Of course, every dipole of any length has a natural resonance, but with the so-called 'twin wire dipole' this does not necessarily have to be within one of the amateur radio bands. Therefore, these dipoles can be described as non-resonant radiators. However, this no longer works when feeding via a coaxial cable. In these cases, the dipole must be fed via a tuned, symmetrical two-wire line. The dipole and the two-wire line form a complete system, which is tuned with a symmetrical antenna coupler to resonance and matching at 50 Ω. This arrangement provides a dipole antenna that can be tuned over a wide frequency range across several amateur radio bands.

With minimal effort to a vertical radiator from antenna wire

Endfed antennas: broadband all-rounders – simple construction, great effect

The current endfed antennas with their broadband matching via a 1:49 UNUN transformer are the renaissance of the well-known Fuchs antenna, which, however, worked with a selective parallel resonant circuit at the time. The common feature is the high-impedance coupling at the end of the half-wave radiator (or a multiple thereof). The advantage of the modernized version is the broadband matching for several bands, which eliminates the need for switching and remote tuning. In particular, the mechanical advantage of feeding at the antenna end is what has made endfed antennas so popular. Compared to dipoles or Windom antennas, the coaxial cable can be fed into the house more easily and inconspicuously in many cases.

Weatherproof and durable protective enclosures

Now a few tips for building and housing BALUN transformers with the currently most popular transformation ratios 1:1, 1:4, 1:6 and UNUN transformers 1:9 and 1:49 in a protective housing. The problem with DIY is not so much winding the toroidal transformers. The greater challenge is the requirements for a self-built protective housing, such as: light, not too big and bulky, break-proof, weatherproof, splash-proof, waterproof, UV-resistant? With a junction box screwed under a simple “bone-type” end insulator for strain relief and sealed with some unknown compound, it's not easily possible to make it work. Even higher-quality installation boxes made of light metal, with a sealing insert in the lid, will sooner or later be ruined without a ventilation opening with a drip edge on the underside. Because: completely closed is usually not yet sealed. If rainwater does not immediately penetrate from the outside, at least the following happens: during the day, the air in the box warms up in the sun, expands and escapes outside. A vacuum is created, which causes the now humid ambient air to be sucked in when it cools down at night. The moisture condenses in the housing and accumulates over time because it cannot easily escape again in its liquid state. Therefore, the “bucket" construction that is completely open at the bottom is better than trying to seal such a housing in DIY. Mount the ferrite core transformer or just the direct connection of the coaxial cable at the bottom of a cup-shaped container. Remember to provide strain relief for the coaxial cable by tying a loop in the cable tie and securing it to the edge of the housing. Once all the connections have been soldered, spray the inside of this protective pot for the connection or balun with plastic spray. After installation, it is only necessary to ensure that this pot is always mounted or hung with the opening facing downwards. This solution to the problem is simple, inexpensive and effective!

Simple projects for beginners with a big impact

You don't necessarily have to be a great craftsman to get started. If you don't have the proverbial “all thumbs hands”, you too can build the basic versions of wire antennas yourself. Just give it a try, start with a lightweight wire antenna for portable radio on vacation or for the next field day. Once you have developed a taste for DIY and experienced how much can be achieved with relatively little effort, then keep going! You can still build an individual antenna here that may not be available ready-made and can, in the best case, match the manufacturing quality of a commercial product.

Empty toolbox? Everything you need for your next antenna project!

And if the contents of your toolbox don't include all the necessary materials: You can find everything you're missing in the categories of our extensive range. Here, of course, even as an advanced semi-pro, you'll find all the materials and accessories you need for projects as demanding as building a multi-element directional antenna yourself.

Browse the following categories for ideas and tips for your DIY projects.

All photos: Alfred Klüß, DF2BC

September 24, Alfred Klüß, DF2BC