Build an Inverted-L Antenna for 160m and 80m
The inverted-L is the most practical antenna for 160m and 80m that most amateur stations can realistically build. Where a full quarter-wave vertical for 160m demands a 130-foot structure, the inverted-L achieves similar low-band performance using whatever vertical height is available — a 60-foot tree, tower, or push-up mast — and runs the remaining wire horizontally to reach quarter-wave electrical length. It requires no exotic components, no loading coils, and no elaborate support structures. Fed against a radial ground system with a simple matching network, the inverted-L delivers genuine low-angle DX radiation on both 160m and 80m from a structure that fits in a typical rural or suburban lot. This guide covers the physics, wire dimensions, radial system, matching options, dual-band operation with a relay-switched capacitor, and the complete installation procedure.
How the Inverted-L Works
The inverted-L is a quarter-wave monopole in an L-shape — the wire starts vertically from the feedpoint, rises to the available support height, then bends 90° and continues horizontally to achieve the total quarter-wave electrical length. The horizontal section acts as a combination of top-loading and additional radiator. The feedpoint is at the base of the vertical section, fed against a radial ground system:
Radiation Pattern — Vertical vs Horizontal Section
The inverted-L's radiation pattern is a combination of the vertical section's low-angle vertical polarisation and the horizontal section's higher-angle horizontal polarisation. The relative contribution of each section depends on the vertical-to-horizontal length ratio:
Why the Inverted-L Outperforms a Loaded Vertical
Many operators compare the inverted-L against a base-loaded or top-loaded shortened vertical of the same physical height. The inverted-L wins on efficiency for a fundamental reason: the horizontal section carries current that contributes to radiation, while loading coils and capacity hats do not radiate — they only change the antenna's electrical length:
Dual-Band Operation — 160m and 80m from One Antenna
The inverted-L naturally operates on 80m as well as 160m. On 80m, a 160m quarter-wave inverted-L is approximately 5/8-wave — longer than optimum but still an efficient radiator. The feedpoint impedance changes significantly between bands, requiring either a switchable matching network or an ATU:
| Support height | Vertical section | Horizontal section (160m) | Total wire (160m) | Horizontal section (80m) | Rr (160m approx) | Est. efficiency |
|---|---|---|---|---|---|---|
| 40 ft (12.2 m) | 40 ft | 88 ft | 128 ft | 21.5 ft | ~15 Ω | ~65% (good radials) |
| 50 ft (15.2 m) | 50 ft | 78 ft | 128 ft | 11.5 ft | ~20 Ω | ~72% (good radials) |
| 60 ft (18.3 m) | 60 ft | 68 ft | 128 ft | 1.5 ft* | ~28 Ω | ~80% (good radials) |
| 70 ft (21.3 m) | 70 ft | 58 ft | 128 ft | — | ~33 Ω | ~84% (good radials) |
| 80 ft (24.4 m) | 80 ft | 48 ft | 128 ft | — | ~38 Ω | ~87% (good radials) |
| 100 ft (30.5 m) | 100 ft | 28 ft | 128 ft | — | ~45 Ω | ~91% (good radials) |
*At 60 ft support height, the antenna is nearly a full quarter-wave vertical on 80m — a very short horizontal section remains. At 70 ft and above, a separate 80m inverted-L configuration with a shorter wire is more practical for 80m operation.
Materials for a dual-band 160m/80m inverted-L using a 60-ft support with relay-switched matching
Building the 160m/80m Inverted-L
This guide builds a dual-band inverted-L on a 60-ft support with relay-switched matching for 160m and 80m. Install the radial system first — it has the largest impact on efficiency. Then erect the vertical support, run the wire, and build the matching network last once feedpoint impedance is measured.
Install the Radial Ground System
The radial system is the single most important factor in inverted-L efficiency on 160m. Install as many radials as possible before erecting the support structure. Radials lie on or just under the ground surface and radiate outward from the antenna base in all directions. For a dual-band 160m/80m inverted-L, radials of 65 feet provide good performance on both bands:
Erect the Vertical Support and Run the Wire
Erect the 60-ft support at the radial plate location. For a fibreglass push-up mast, anchor the base in a sleeve of concrete or a heavy wooden post anchor. For a tower section, follow the manufacturer's installation guide. The support must be stable in wind — the horizontal wire exerts a sideways pull at the top of the mast that adds to wind loading.
Run the antenna wire from the base insulator (mounted at ground level at the radial plate) straight up the support to the top, then horizontally to the far support point. Secure the wire to the vertical support with UV-resistant zip ties every 2–3 feet — keep the wire 2–3 inches away from any metal mast surface to prevent direct contact, which would partially short the antenna. At the top, make a clean 90° bend using a corner insulator, then continue horizontally to the far anchor.
Determine Horizontal Wire Length and Resonance
Before building the matching network, establish the correct total wire length for resonance on 160m. The theoretical length (127.9 ft at 1.83 MHz) is a starting point — the actual resonant length varies with wire height, diameter, horizontal wire height, and ground conductivity at your specific installation:
Build the 160m Matching Network
With the feedpoint impedance known from the NanoVNA measurement, build the L-network to transform the measured feedpoint resistance to 50 Ω. For a feedpoint resistance below 50 Ω (typical for an inverted-L), the L-network uses a series inductor on the high-impedance side and a shunt capacitor on the 50 Ω coax side:
Add Relay-Switched 80m Matching
On 80m the inverted-L presents a high and reactive impedance at the feedpoint — the fixed 160m matching network does not provide a useful match on 80m. A relay-switched capacitor in parallel with the feedpoint, bypassing or augmenting the 160m network, shifts the system to work on 80m. This is the most practical dual-band solution for a permanent installation:
Verify Performance on Both Bands and Weatherproof
With both matching networks installed and adjusted, verify SWR on both bands from the shack end of the coax. Check the relay switching by toggling between 160m and 80m mode and confirming the SWR changes appropriately on each band. Document the SWR curve on both bands:
Weatherproof all outdoor components thoroughly. The matching network enclosure must be fully sealed — condensation inside the enclosure causes capacitor leakage that shifts the 160m resonance unpredictably. Apply silicone sealant to all cable entries and use desiccant packs inside the enclosure, renewed annually. Inspect all connections every spring after the first winter season.
Shunt-Fed Tower as an Inverted-L
If you already have a guyed or self-supporting tower, shunt-feeding it for 160m is an effective way to create an inverted-L without a separate wire running up the tower face — the tower itself becomes the vertical element and a wire extends horizontally from the top for additional length:
- How it differs from wire inverted-L: the tower is grounded at the base (the yagis and rotator are unaffected). A separate feed wire connects to the tower at a height of approximately 1/4 to 1/3 of the way up, with an omega or gamma match providing the 50 Ω connection. The feed wire goes up to the tower and horizontally from the tower top.
- Effective vertical section: the full tower height — typically 60–100 ft — provides the vertical section. The existing yagis on the tower act as inadvertent top loading, often improving 160m performance beyond what the bare tower height suggests.
- Wire from tower top: a single horizontal wire of 30–60 ft from the tower top extends the electrical length on 160m. This horizontal wire is the "L" portion of the shunt-fed tower inverted-L.
- Reference: the W8JI website documents shunt-fed tower techniques for 160m in extensive detail and is essential reading for operators considering this approach.
Horizontal Wire Direction — Does It Matter?
The direction the horizontal section points affects the inverted-L's radiation pattern — but less than most operators expect:
- Pattern asymmetry: the horizontal wire introduces a slight forward tilt in the radiation pattern — the antenna radiates slightly more strongly in the direction the horizontal wire points than directly away from it. This asymmetry is typically 2–4 dB on 160m at low angles.
- Practical significance: for a US station wanting to work Europe, pointing the horizontal wire eastward adds a small amount of gain toward Europe. This is a minor optimisation compared to getting the vertical section as tall as possible.
- Constraint from lot layout: in most installations the horizontal wire direction is constrained by the available space and support points. Do not sacrifice vertical height (the dominant performance factor) just to point the horizontal wire in a preferred direction. Vertical height matters far more than horizontal wire direction.
- Multiple horizontal directions: some operators run two horizontal wires in opposite directions from the same support, switched with a relay. This allows choosing between two preferred DX directions without moving the antenna. The switching relay grounds the unused wire while the active wire is connected to the matching network.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| No resonance visible on 160m sweep | Open circuit — wire break, base insulator failure, or matching network fault | Check DC continuity from feedpoint through wire to far end; check base insulator for cracks; check matching network connections | Repair wire break; replace cracked base insulator; re-solder matching network connections |
| Resonance shifts 50–100 kHz seasonally | Ground moisture changes effective electrical length; or wire sags in heat changing horizontal length | Compare resonance spring vs autumn; measure SWR on a hot day vs cold day | Accept seasonal shift as normal (±30 kHz is typical); adjust matching network tap or relay capacitor seasonally if needed |
| Good SWR but very poor 160m performance — low WSPR spots | Inadequate radial system; base insulator leakage; or antenna wire touching mast | Measure ground resistance at radial plate; inspect base insulator; check wire clearance from metal mast | Add more radials to minimum of 32; replace leaky base insulator; add spacers to keep wire away from mast |
| 80m relay switching not working — same SWR both positions | Relay not energising; or relay wired incorrectly in the matching network | Measure DC voltage at relay coil terminals with toggle switch on — should be 12V | Repair DC control wiring; verify relay wiring connects 80m capacitor correctly across feedpoint |
| SWR rises significantly at 100W+ but fine at low power | Capacitor voltage rating too low; or component lead lengths too long creating resonance | Transmit 100W CW and listen for arcing; check capacitor for burn marks | Replace capacitor with higher-voltage-rated unit; shorten all component leads to under 1 inch |
| RF feedback in shack on both 160m and 80m | Common-mode current on coax — matching network ground not connected to radial plate | RF tingle on equipment chassis; check that coax shield connects to radial plate through matching network | Verify coax shield to radial plate connection in matching network; add ferrite choke on coax at shack entry (8 turns through FT-240-31) |
| Horizontal wire sagging — resonance shifted below 160m CW band | Wire elongated in heat or ice loading; support rope stretched | Measure horizontal wire length; compare to original installation length | Replace nylon rope with Dacron (Dacron does not stretch); retension horizontal wire; trim if necessary to restore resonance |
Does the horizontal wire direction affect DX performance significantly?
The effect is real but modest — typically 2–4 dB asymmetry at low angles depending on the horizontal wire direction. Pointing the horizontal wire toward your primary DX target adds a small directional advantage, but maximising the vertical section height has a far larger impact on 160m DX performance than wire direction. If you must choose between a taller vertical section (which requires a shorter, differently-directed horizontal section) and a longer horizontal section pointed toward Europe, always choose the taller vertical. Vertical height is the dominant variable in inverted-L performance.
Can I use the inverted-L on 40m and higher bands?
On 40m the 128-ft inverted-L is approximately 1.25 wavelengths — an odd multiple of a quarter-wave. It resonates and can be matched with an ATU, making it usable on 40m as a high-angle antenna (the pattern on 40m is complex with multiple lobes). On 20m and above the antenna becomes electrically long and the radiation pattern degrades into multiple high-angle lobes — not ideal for DX but usable with an ATU for general operation. Many 160m/80m inverted-L operators run the antenna on all bands with a shack ATU and accept the pattern compromises on the higher bands, using it primarily as a 160m/80m specialist antenna and having separate antennas for 40m through 10m.
How many radials do I really need?
The practical minimum for a useful inverted-L is 16 radials — below this the ground loss dominates. For serious 160m operation, 60 radials is the commonly recommended target. The efficiency gain from 16 to 32 radials is approximately 2–3 dB — equivalent to doubling transmit power — and is easily worth the labour of laying the additional wire. Beyond 60 radials the improvement per additional radial is small. The most practical advice: install as many radials as you can in the available space. Even 24 radials of 50-ft length makes a dramatically better 160m inverted-L than 8 radials of any length.
Is the inverted-L better than a dipole on 160m?
For DX — unequivocally yes. A dipole at typical amateur heights (under 100 feet) on 160m radiates primarily straight up, making it an excellent NVIS antenna for regional contacts within 500–2,000 miles but a poor DX antenna. The inverted-L, fed against a good radial system, radiates at low angles along the ground — the key to 160m DX propagation. Even a modest inverted-L with 32 radials on a 50-ft support will outperform a full-size 160m dipole at 100 ft for transcontinental and intercontinental DX contacts. For regional contacts within 1,000 miles, the high-angle dipole may perform comparably or better.
What is the minimum support height for a useful 160m inverted-L?
The practical minimum vertical section for a useful 160m inverted-L is about 40 feet. Below this height the vertical section is only 31% of a quarter-wave, the radiation resistance is very low (around 10–15 Ω), and efficiency drops even with a good radial system. At 40 feet with good radials, the inverted-L still significantly outperforms a 160m dipole for DX. At 50–60 feet it becomes a genuinely competitive 160m antenna. At 70–80 feet or taller it is an excellent 160m antenna by any standard. If your tallest available support is only 30–35 feet, consider adding top-loading (a T-hat at the support top) to increase the effective electrical height before the wire bends horizontal.
Do I need a separate antenna for 80m or can I rely on the inverted-L?
The inverted-L works well on 80m with appropriate matching and is a genuine all-round 80m antenna — not just a 160m antenna pressed into dual-band service. On 80m the 128-ft wire is approximately 5/8-wave, which produces efficient radiation at moderate elevation angles with some low-angle DX capability. Many operators use the inverted-L as their primary 80m antenna and find it fully competitive with a dipole at similar heights. For serious 80m DX contesting, a pair of phased verticals or a 4-square array will outperform the inverted-L — but for general operation including DX, the dual-band inverted-L is a highly practical single-antenna solution for both low bands.