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These are sometimes known as a Magnetic Longwire Balun. Its really an impedance transformer (9:1) to feed a high impedance, end fed (unbalanced) random wire which is likely to be a few hundred ohms, and transform it into something closer to a 50Ω (unbalanced) coaxial input, hence UnUn.
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Figure 2 Schematic of the 9:1 voltage unun. Typically unbalanced = 50/75 ohms too unbalanced = 450/675 ohms. Figure 3 Wiring of the 9:1 voltage unun. Note this drawing shows winding connections and not the number of turns required. See article for details.
The heart of the Un-un uses a Type 43 [FT240-43] core and consists of a trifilar [3 wire] winding arrangement around the core. The wires are wound to create a 9:1 transformer and would ideally suit an end-fed long wire antenna fed against ideally – a good counterpoise, or a good radial system.
Start with the end of the wire in the center of the toroid and begin winding as shown in the image to the right. Make about 7-10 full turns, evenly spaced around the toroid. The starting end of the wire will solder to the “GND” pad on the PCB.
Figure 1 Typical 9:1 voltage unun and long wire antenna configuration. Construction . 1.25mm Enamelled copper wire was used in a triple bifilar winding of 4 turns wound evenly spaced around the L15 ferrite toroid core with the three individual windings wound close together.
21 maj 2022 · With no goals and constraints, here is a coaxial wound 9:1 UnUn. Performance is very poor. and also. The first link shows the typical 9:1 UnUn while your second link is about BalUns. I assumed from the title, the goal was to make an UnUn. Specifically a 9:1. The OP was only testing from 3-30MHz, with a worse case VSWR of 1.4:1.
14 kwi 2002 · Wind 9 turns around the core with the three wires. I used a couple of small zip ties on either end of the windings to hold everything in place. Now, solder up the wires as follows: Red wire on left side of unun winding and green wire on right side of winding goes to BNC "hot".
