UA4HAZ 20 Meter Folded Dipole Antenna – For many amateur radio operators, the 20-meter band is the “money band.” It is the workhorse of the high-frequency spectrum, offering reliable long-distance propagation during the day and often remaining open well into the night during the peak of the solar cycle. However, a standard half-wave dipole for 20 meters requires approximately 10 meters of horizontal space.
While that might sound modest, many modern suburban lots, apartment balconies, or densely wooded yards simply cannot accommodate a straight wire of that length. This is where the UA4HAZ 20 Meter Folded Dipole Antenna design enters the fray, offering a “folded” geometry that provides a elegant solution to the perennial problem of limited real estate.
Geometry of the UA4HAZ Design
The antenna illustrated in our schematic is a variation of a loaded or bent dipole. In a traditional horizontal dipole, the wire stretches out in a single straight line. The UA4HAZ approach takes that 10-meter span and breaks it into three distinct segments: a central horizontal section and two vertical “tails” that drop down at 90-degree angles. According to the specific dimensions provided, the horizontal section spans 5.32 meters (composed of two 2.66-meter arms), while the vertical drops each measure 2.6 meters.
When you sum these components, you find a total radiator length that approximates the standard formula for a half-wave resonance. The genius of this “inverted-U” or “Moxon-like” fold is that it concentrates the highest current portion of the antenna—the center—at the highest possible point. Since the center of a dipole is responsible for the majority of the radiation, keeping this part horizontal and elevated ensures that you maintain a predictable radiation pattern and a relatively low angle of radiation, which is essential for DX (long-distance) communication.
Folded Dipole Antenna :The Physics of the Fold
Folding an antenna is never “free” in terms of physics. When you bend the ends of a dipole downward, several things happen simultaneously. First, the mutual capacitance between the ends of the wire and the ground increases. This usually means that a bent antenna will appear electrically longer than a straight wire of the same physical length. Consequently, the dimensions provided—2.66 meters for the horizontal arms and 2.6 meters for the drops—are carefully calculated to balance this effect for the 14 MHz range.
Secondly, folding the ends changes the radiation resistance. A center-fed dipole in free space typically exhibits an impedance of about 72 ohms. By folding the ends toward the ground, the impedance generally drops. Fortunately for the modern ham, this drop often brings the antenna closer to the 50-ohm characteristic impedance of standard coaxial cables like RG58 or RG213. This simplifies the matching process, as it often eliminates the need for complex 4:1 baluns or external tuners, provided the antenna is mounted at a reasonable height.
Step-by-Step Construction and Material Selection
Building this Folded Dipole Antenna requires minimal investment but demands attention to detail, particularly regarding the wire gauge and insulation. The schematic specifies a 3-mm diameter wire. While you can use thinner 14-AWG house wire, the 3-mm thickness (roughly 8 or 9 AWG) provides better structural integrity and a slightly wider bandwidth. Thick copper wire or “copperweld” is ideal because it resists stretching under the tension of the horizontal span.
To begin construction, measure out two lengths of wire, each approximately 5.3 meters long. This gives you enough excess to create the loops for your center insulator and the end insulators where the wire bends downward. The bend itself should be supported by a non-conductive spacer or a lightweight PVC frame if you want to maintain a crisp 90-degree angle. However, in many field installations, simply let the wire hang naturally after passing through an insulator at the 2.66-meter mark.
Correcting the Coaxial Feed: The Heart of the System
One of the most common mistakes in DIY antenna building is the improper termination of the coaxial cable. As noted in the corrected diagram, a 50-ohm coax like RG58 consists of a center conductor and an outer braided shield. To feed this dipole correctly, you must treat these two components as individual wires.
You should strip back about 5 centimeters of the outer black jacket. Carefully unbraid the copper shield and twist it into a tight “pigtail.” This pigtail becomes your second conductor. Strip the inner dielectric to reveal the center copper pin. In the UA4HAZ folded dipole antenna design, the center pin is soldered to the right-hand arm of the dipole, and the twisted pigtail shield is soldered to the left-hand arm.
This transition from a coaxial (unbalanced) line to a dipole (balanced) radiator technically benefits from a 1:1 choke balun—which can be as simple as six to ten turns of the coax itself coiled into a 10-cm diameter circle near the feed point. This prevents “RF on the shack,” where the outside of your cable becomes part of the antenna and causes interference with your electronics.
Folded Dipole Antenna : Installation Heights
The performance of the UA4HAZ folded dipole antenna is heavily dependent on its height above ground. Because the ends of the antenna drop down 2.6 meters, you need to ensure the horizontal section is high enough so that the tips of the “tails” are not touching the ground or within reach of people or pets. RF burns are a real risk, even at modest power levels. Ideally, the horizontal span should be at least 7 to 10 meters high. This keeps the high-voltage ends of the antenna well above head height and reduces ground losses.
If you are forced to mount the antenna lower, you will likely notice that the resonant frequency shifts downward. This is due to the increased capacitive coupling with the earth. In such cases, you may need to “prune” the vertical tails. Trimming just 2 or 3 centimeters at a time from each side can move the SWR (Standing Wave Ratio) “sweet spot” from the bottom of the band up into the SSB (Single Sideband) portion of the 20-meter band.
Why Choose This Design Over a Vertical?
Many space-constrained hams immediately look toward vertical antennas. While verticals have a small footprint, they often require an extensive (and sometimes frustrating) radial system of wires laid out on the ground to be effective. The UA4HAZ folded dipole antenna is a self-contained system. It does not require a ground plane or radials to function. Furthermore, because it is primarily horizontal, it tends to be much quieter in terms of man-made noise. Vertical antennas are notorious for picking up “hash” from LED lights, switching power supplies, and neighborhood electronics. The dipole’s inherent balance helps reject some of this local interference, providing a clearer path to those weak DX signals.
Final Tuning and Operation
Once the antenna is hoisted, the first step is to check the SWR across the 14.0 to 14.35 MHz range. A successful build should show an SWR of 1.5:1 or lower at the center of the band. If the resonance is too low, shorten the vertical tails. If it is too high, you might need to add a small “fuzz” of wire to the ends or lower the antenna slightly to increase ground coupling.
The UA4HAZ 20-meter folded dipole antennais more than just a compromise; it is a smart piece of engineering that proves you don’t need a massive tower to participate in global communications. Whether you are operating QRP (low power) from a park or running 100 watts from a suburban home, this antenna provides a reliable, easy-to-build gateway to the world. By following the corrected wiring diagram and ensuring your connections are weatherproofed with self-amalgamating tape, you will have a durable radiator that will serve you through many seasons of sunspots.
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