For amateur radio operators, the quest for a versatile yet simple HF antenna often leads to complex multi-band traps or expensive vertical systems. However, some of the most effective solutions are found by revisiting and refining classic designs. One such standout is the 3-band asymmetrical dipole, a clever modification of the legendary DL1BU HF antenna. This design is specifically engineered for peak performance on the 40m, 20m, and 10m bands, offering a streamlined approach that eliminates the need for cumbersome symmetric feeders.
The brilliance of this HF antenna lies in its simplicity and accessibility. Originally envisioned by the late antenna specialist Guenter Schwarzbeck (DL1BU), this modern adaptation by OK1IKE utilizes a single coaxial feed line and a custom-wound toroid transformer. The physical construction consists of two wire legs: a longer section of 14 meters and a shorter section of 6.7 meters. While historical data often suggested a 300-ohm impedance for this configuration, modern software modeling and practical field tests have confirmed that the impedance at the feed point actually sits closer to 150 ohms.
To bridge this to a standard station, the design employs a specialized toroid balun. According to the original documentation, a transformer wound on a core with a 2 cm² cross-section works exceptionally well. For those using 75-ohm cable, the recommended winding ratio is 15 turns on the primary side and 30 turns on the secondary side using 1 mm wire. However, most modern operators using 50-ohm RG-8X or similar coaxial cables will find that a 1:4 or even a 1:2 voltage balun provides the most stable match across all three bands.
3-Band HF Antenna Performance
The performance results of this modification are impressive and highly reliable. Users can expect an excellent Standing Wave Ratio (SWR) of 1.1:1 on the 40m band, approximately 1.3:1 on 20m, and a manageable 1.8:1 on the 10m band. This makes it a “forgiving” antenna that performs brilliantly even without a high-end external tuner. By focusing on the precise trimming of the 14m and 6.7m legs and ensuring high-quality insulation at the center and end points, you can create a durable, high-gain radiator. This project is not just a tribute to the legacy of DL1BU, but a practical, high-performance tool for any ham looking to maximize their reach across the HF spectrum with minimal fuss.
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