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Constructing an HF End-Fed Half-Wave (EFHW) vertical antenna, the resource details the winding of a monoband matching unit, inspired by _AA5TB_, designed to provide a 50 Ohm impedance match without a ground plane or antenna tuner. It specifies the use of a _T200-2_ ferrite core for the transformer, outlining the 13-turn secondary and 2-turn primary winding process with enamelled copper wire. The document also describes the integration of a coax capacitor, whose length is critical for tuning and varies by band, with specific starting lengths provided for 20m, 17m, 15m, 12m, and 10m operation. The practical application section guides the builder through tuning the antenna using an antenna analyzer, emphasizing the iterative process of spacing secondary windings and trimming the coax capacitor to achieve resonance at the desired band frequency. It highlights the antenna's low angle of radiation, beneficial for DX, and claims up to 2 S-points improvement over a _G5RV_ or similar doublet when used as an omnidirectional vertical. A comprehensive shopping list, including specific part numbers from _Rapid Electronics_, is provided, along with advice on selecting fiberglass fishing poles for support and suitable antenna wire.

One point eight MHz to 30 MHz is the operational bandwidth for this 4:1 Ruthroff voltage balun, designed to interface an unbalanced T-Match network with a balanced antenna system. The project details the construction using a _T200-2_ powdered iron toroid core, tightly wrapped in PVC electrical tape for insulation, and wound with 17 double bifilar turns of 1.25mm enamelled copper wire. This outboard balun offers flexibility, allowing hams to trial various baluns based on antenna system and impedance characteristics, rather than integrating it directly into the tuner. The resource includes a schematic of the balun, a wiring diagram showing winding connections, and a table suggesting alternative toroid cores like the T80-2 or T400-2 with corresponding winding counts. Component sourcing is straightforward, listing items such as the _Amidon_ T-200-2 core, SO-239 connector, and a sealed polycarbonate enclosure from Jaycar. Performance evaluation was conducted using an _AIM 4170C_ antenna analyser, demonstrating efficient 1:4 voltage transformation across the specified HF spectrum. Further efficiency tests involved measuring RF power loss at various frequencies, revealing minimal loss—less than 0.7 dB from 3.6 MHz to 30 MHz, and only 2.0 dB at 1.8 MHz. These measurements, performed under ideal 50-ohm conditions, confirm the balun's effectiveness as a low-loss interface for multi-band antenna systems. The page also links to several other balun and unun projects, including 1:1 current and voltage baluns, and 9:1 voltage ununs, providing a broader context for impedance matching solutions.

Constructing an End-Fed Half-Wave (EFHW) antenna offers a practical solution for HF operators seeking a multiband wire antenna without the need for extensive radial systems. This design typically employs a high-impedance transformer at the feed point, matching the antenna's inherent high impedance to a 50-ohm coaxial feedline. The article specifically details a 2012 approach, focusing on a transformer with a 49:1 turns ratio, which is a common configuration for EFHW antennas. The resource outlines the construction of a wire element cut for a half-wavelength on the lowest desired band, with specific coil arrangements enabling operation on harmonically related bands such as 40m, 20m, and 10m. It discusses the physical dimensions and winding details for the matching transformer, often utilizing a ferrite toroid core to achieve the necessary impedance transformation. The content provides insights into the operational principles and practical considerations for deploying such an antenna, including methods for tuning and optimizing performance across multiple amateur radio bands. While acknowledging that the presented information from 2012 may be superseded by newer insights, it serves as a foundational reference for understanding EFHW antenna theory and construction.

Article about isolation transformer construction to perform optimal impedance matching. Winding the FCP isolation transformer, includes interesting table for Winding Turns and Lengths and Core Configurations for T300 T200 T400 toroids

Building an End-Fed Half-Wave (EFHW) antenna from a kit, as detailed by Frank Bontenbal, PA2DKW, with process photos by Bob Inderbitzen, NQ1R, offers a practical approach for hams. This specific kit, a collaboration between ARRL and HF Kits, targets 10, 15, 20, and 40 meters, making it a versatile option for HF operations. Unlike a center-fed dipole, the EFHW is a half-wavelength antenna fed at one end, which simplifies deployment, particularly for portable use. The construction guide meticulously outlines the assembly of the 49:1 impedance matching network, crucial for transforming the antenna's high impedance (around 2,500 Ohms) to a transceiver-friendly 50 Ohms. Steps include preparing the enclosure by drilling holes for the coaxial connector and antenna connections, followed by the precise winding of enameled copper wire onto a toroid to create the transformer. The guide emphasizes careful insulation removal and soldering for reliable connections. Final assembly involves integrating a 100 pF capacitor for higher band compensation, soldering the transformer's primary and secondary sides, and conducting SWR tests with a 2K7 resistor or a half-wavelength wire. The document also provides examples of wire lengths for different bands, such as 16 feet for 10 meters or 66 feet for 40 meters, demonstrating the transformer's adaptability for various half-wavelength configurations.

This PDF article introduces a series of dual-tuned bandpass filters designed for input tuning in amateur band receivers. Developed by Stefen Niewiadomski, these filters feature 50-ohm input/output impedance and can be cascaded for improved roll-off outside the passband. The designs use readily available TOKO coils, with taps on the tuned winding for matching input circuits with impedances around 1k ohm. The inductors are core-tuned, with average inductance values provided for easier matching to other inductors.