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4 cze 2021 · Easiest way to find out is to build it and measure empirically. Using triple windings allows closer wire spacing between the transformer input and output (primary and secondary) windings which can improve the magnetic coupling coefficient.
12 sie 2016 · It’s relatively easy to build a 9:1 balun. One of the most common designs is to wind nine turns of a trifilar winding around a toroid core. Trifilar means that there are three wires wound simultaneously around the core.
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.
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.
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.
21 maj 2022 · I swept from 400Khz to 4MHz. Again, I'm just using that box of resistors to get some idea how the transformer behaves. At 4MHz the LiteVNA is showing a VSWR of 1.32:1 which I expect if due to the load.
The "9:1 UNUN" are for random length wire antennas fed at the end. 49:1 or other high ratio transformers are for resonant "cut to frequency" antennas like the traditional zepp/fuchs antenna.
