Random Wire & End-Fed Antennas
Overview
End-fed wires are the dominant HF antenna of the post-2010 amateur era — the end-fed half-wave (EFHW) with a 49:1 ferrite-toroid UNUN gives a "single end-support, one feedline, no center insulator, no radial field" antenna covering four bands at usable SWR without a tuner. This dive covers the resonant EFHW (high-voltage end-impedance ≈ 2450 Ω, 49:1 or 64:1 UNUN, harmonics on 40/20/15/10 m), the non-resonant random wire and long wire with a 9:1 UNUN plus tuner, and the sloper and inverted-L geometric variants. UNUN topology, ferrite-core selection, and core saturation under sustained TX are treated at transformer-designer depth. The DIY build is a 40 ft EFHW for 40/20/15/10 m; commercial buys are ranked from $30 kit to $300 engineered unit.
Context
The EFHW is the backpack-portable HF antenna — deploy a real station in 90 seconds from a backpack with no center support — and the stealth antenna for HOA-restricted lots where a visible center insulator is problematic. The UNUN is the load-bearing component: it is what separates the $30 EFHW kits (undersized ferrite, core saturation at 50 W sustained) from the $300 engineered units (adequate core for 100 W sustained). The random-wire-plus-9:1 variant is the all-band receive antenna for any SDR; the 9:1 UNUN winding guide cross-links to the companion BALUNs & UNUNs sub-project for deeper ferrite treatment.
