Low-Band EFHW Inverted-L
On 160, 80, and 40 meters, a lot of “EFHW advice” is really just the same 49:1 story repeated across every band. The RF.Guru position is different: on the low bands, the installed end impedance of an inverted-L often lands in the several-kΩ region, so the transformer ratio should follow the real impedance target, not a copy-paste default.
(The goal here is not a slogan like “radial-free.” The goal is a stable RF system: a sensible ratio, a short defined return path, and controlled common-mode.)
160/80 m EFHW Inverted-L with 68:1
On 160 and 80 meters, my go-to TX antenna is not the classic 49:1 EFHW. It is a dedicated RF.Guru-style inverted-L cut as a true 160/80 dual-band wire, using a 68:1 transformer because that ratio tracks the real installed end impedance of this geometry far better than the usual 49:1 assumption. In serious 160/80 inverted-L installs, the end impedance often lands in the several-kΩ region, so 68:1 is not a gimmick — it’s simply the right engineering target when the goal is lower mismatch stress, better efficiency, and more repeatable behavior on the low bands.
Return path and choking
I would never explain these antennas as “radial-free magic.” They still need a return path, but in the RF.Guru approach that return is kept short, intentional, and defined instead of being handed over to a big buried radial field or left to chance on the outside of the coax. A short counterpoise or local RF reference, together with a 1:1 choke placed about 0.05 λ down the coax, makes the system far more stable and stops the feedline from becoming the uncontrolled counterpoise.
Why it works so well in real low-band yards
Performance-wise, this is a strong low-band transmitting antenna because the vertical section supports the low-angle radiation needed for DX, while the horizontal section still contributes useful higher-angle energy for regional coverage. Just as important, it avoids the biggest weakness of short or radial-starved low-band verticals: on 80 and 160 meters, ground and loading losses can eat a large part of the RF when radiation resistance is low and current is concentrated near the base. The 160/80 EFHW inverted-L pushes the system toward a more efficient current distribution, is less dependent on perfect ground, and is therefore often the better real-world DX choice from a single wire.
Two practical ON6URE notes
Ferrite choice: On 160/80, Mix 77 is often a logical match for the transformer because it helps deliver the needed inductance without excessive turns.
Mast height trade: Around 20 m tends to shift the antenna more toward DX-leaning angles, while ~15 m often keeps a bit more regional/NVIS energy and is mechanically easier. (Exact behavior still depends on the horizontal run, nearby conductors, and how the return path is defined.)
80/40 m EFHW Inverted-L with 70:1
For 80/40 meters, I stay with the same philosophy: a dedicated EFHW inverted-L, but now with a 70:1 transformer. Again, the reason is not dogma but installed impedance. In this geometry, the 80/40 wire often presents a several-kΩ end impedance that maps much more cleanly to 50 Ω with about 70:1 than with a copied 49:1 design. That gives lower SWR, less mismatch stress, more predictable deployment, and better high-power robustness than the “one ratio fits all bands” mindset.
DX plus regional utility
This band pair is especially attractive because it covers both DX and useful regional work. On 40 meters, the vertical section helps launch energy at lower angles for long-haul paths. On 80 meters, the horizontal leg still contributes meaningful high-angle radiation, so the antenna is not just a DX tool — it also remains useful for shorter-range contacts and some NVIS-style work. That balance is exactly why I prefer it over a short 80-meter vertical or a purely horizontal wire when I want one transmit antenna that leans toward DX but still stays versatile.
Build it as a complete RF system
The key is to treat it as a system: correct transformer ratio, short defined return path, and proper choking. Use a short counterpoise or local reference, and place a 1:1 current choke about 0.05–0.1 λ down the coax. If you do not define the return path, the station will define one for you — usually on the outside of the coax — and that is when you get shifting SWR, pattern changes, and RF in the shack. Built properly, the 80/40 inverted-L becomes one of the most practical and contest-friendly low-band TX antennas you can deploy.
Choke placement — what “0.05 λ” looks like in practice
- 160 m: 0.05 λ is typically on the order of ~8 m of feedline distance.
- 80 m: 0.05 λ is typically on the order of ~4 m of feedline distance.
- Rule of thumb: measure along the coax route, not “as the crow flies.” Keep it practical, accessible, and mechanically tidy.
(This is about controlling common-mode and stabilizing the system. It’s not a magic number, but it’s a consistently useful starting point.)
Practical checklist
- Choose a ratio that matches the installed end impedance: 68:1 for 160/80, ~70:1 for 80/40 in this inverted-L geometry.
- Define the return path: use a short counterpoise/local RF reference rather than “letting the coax decide.”
- Control common-mode: add a real 1:1 current choke at ~0.05–0.1 λ down the feedline.
- Expect small shifts: height, nearby conductors, and routing always move resonance and SWR a bit on the low bands.
Mini-FAQ
- Why 68:1 or 70:1 instead of 49:1? Because the installed end impedance of these low-band inverted-L geometries is often several kΩ, and the ratio should track the real target for lower mismatch and more repeatable behavior.
- Do I still need radials? You need a return path. The RF.Guru approach is a short, intentional counterpoise/local RF reference so the outside of the coax doesn’t become the “surprise return.”
- Where should the 1:1 choke go? A strong starting point is ~0.05 λ down the coax (and sometimes up to ~0.1 λ), placed where it’s practical and mechanically secure.
- Is this only a DX antenna? No. The vertical section supports low-angle radiation, while the horizontal section contributes higher-angle energy that remains useful for regional coverage (especially on 80 m).
- What causes unstable SWR and RF in the shack? An undefined return path and uncontrolled common-mode on the feedline. Define the return, then choke the coax so the antenna behaves like an antenna, not a “house wiring experiment.”
- Can I run high power? Yes, if the transformer and choke are designed for the power level and heat, and if the install is mechanically sound. Lower mismatch stress helps, but QRO still demands proper materials and conservative design.
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