Inverted L Antenna: A Practical Low-Band Wire Vertical

The low bands have a way of humbling station builders. A full-size quarter-wave vertical for 160 meters is around forty metres tall, and few gardens come with a mast that high. The inverted L antenna is the classic compromise: a vertical wire as high as your support allows, bent at the top into a horizontal section so that the total length reaches a quarter wavelength. It is cheap, easy to build from wire and has been a favourite of low-band DXers for decades. This guide explains how the antenna works, what shape and size to aim for, why the ground system matters as much as the wire, how to feed and match it, and how to stay safe around a wire that carries high voltage.

If you are still deciding what to put up for the top band, read it alongside our general guide to 160 meter DXing. The inverted L is not the only choice, but it is one of the few that a typical suburban plot can accommodate.

What an Inverted L Is

An inverted L is a monopole antenna: a single radiating wire worked against a ground system. It resembles the letter L turned upside down. A vertical wire rises from the feed point, and a horizontal wire continues from the top. As the encyclopedia entry on T-antennas and inverted-L antennas explains, the inverted-L is similar to the T-antenna, except that the vertical feeder is attached at one end of the horizontal top-load wire instead of the centre. The same source notes that these antennas are typically used on the long-wave, medium-wave and shortwave bands and are widely used as transmitting antennas for amateur radio stations.

Both antennas work as monopoles with capacitive top-loading. The horizontal section acts like the plate of a capacitor and allows more current to flow in the vertical section, and it is the current in the vertical section that does most of the useful radiating. The inverted L is weakly directional, with maximum radiation in the direction of the top-load wire.

Because the radiation comes mainly from the vertical wire, the antenna has a low take-off angle, which is what you want for long-distance work on the low bands. The horizontal wire also radiates a horizontally polarised component, so the antenna produces a mixture of polarisations, which can be an advantage when signals arrive with varying polarisation.

How Big Should It Be?

The antenna is resonant when the total length of wire, vertical plus horizontal, is close to a quarter of a wavelength. A useful starting point is the quarter-wave formula in metres: about 71.3 divided by the frequency in MHz. Treat the results below as a first cut to be trimmed with an antenna analyzer, because the real resonance depends on height, nearby objects, wire diameter and ground quality.

The golden rule is to make the vertical section as tall as practical. The vertical wire does most of the radiating, so every extra metre of height in the vertical part improves efficiency. A short vertical with a long horizontal wire works, but it behaves more like a loaded antenna, with less radiation resistance and more loss in the ground system. Height also lowers the take-off angle, which is the reason the low-band DXer climbs every tree in the neighbourhood.

The Ground System Is Half the Antenna

Any monopole needs something to push against. W8JI, a well-known low-band antenna builder, lists the jobs of an antenna ground on his page about antenna grounds: it provides the other terminal for the feed point of Marconi-style or single-wire end-fed antennas, it provides a low-loss return path for the displacement currents caused by the antenna’s electric field and an alternative path for currents that would otherwise flow in lossy soil. For an inverted L, that means radials or a counterpoise.

A few rules of thumb apply:

• A ground rod is not a radial system. A rod gives a safety and lightning connection, but the return path for the antenna current is the job of the radials. The same builder’s page on ground systems lists a controlled RF return path for end-fed, single-wire-fed antennas as one of the primary functions of a ground system, separate from lightning protection and safety.
• More radials beat longer radials. Many wires of moderate length reduce ground loss better than a few long ones. Our article on vertical antenna radials goes through the numbers and the trade-offs.
• Raised radials work too. If you cannot bury wires, elevated radials above the soil act as a counterpoise. They must be insulated from walkers and animals.
• Symmetry helps. Spread the radials evenly around the base so that no single direction takes the full return current.

The efficiency of a low-band vertical is dominated by ground loss. If you must choose between a better wire and more radials, choose more radials.

Feeding and Matching

An inverted L is fed at the bottom, between the base of the vertical wire and the ground system. A good starting point is a coaxial cable from the shack to a small box at the base. The impedance at the feed point depends on the geometry, the height of the vertical part and the quality of the ground, so measure it rather than assume it.

In practice there are three common ways to match the antenna:

1. Tune it to resonance and feed directly. Trim the wire so that resonance falls where you operate, and check the standing wave ratio with an analyzer. If the match is not close to 50 ohms, adjust the radial system or add a simple matching network.
2. Use an L-network or tuner at the base. A matching network at the feed point lets you resonate the antenna on a wider frequency range. Our article on external antenna tuners explains when a tuner at the antenna is better than one in the shack.
3. Use a remote tuner. For multi-band operation, an automatic tuner at the base keeps losses low and lets you change bands from the shack.

If you try to use a 160 meter inverted L on 80 meters, remember that the wire is then close to a half wavelength long and the feed point impedance can be very high. A matching network designed for such loads is needed, and losses will be higher than on the design band.

Building It Step by Step

1. Choose the support. A tall tree, a mast or a tower can support the top of the vertical section. Use a pulley or a non-rotting rope so you can lower the wire for adjustment.
2. Pick the wire. Insulated or bare stranded copper or copper-clad steel wire works. Use a gauge that will survive wind and the weight of ice, and test the tension before you commit.
3. Plan the horizontal part. Keep it clear of the vertical wire and away from metal objects. A horizontal section that slopes down toward the far end is common when height is limited.
4. Insulate the ends. Use proper insulators at the far end and at the support. Remember that the far end of a quarter-wave antenna sees the highest voltage.
5. Install the radial system. Lay or elevate radials in a symmetric pattern from the base, and connect them to a common bonding plate.
6. Add common-mode protection. Place a choke on the feed line near the base to keep currents off the coax. Our article on common-mode chokes covers the details.
7. Tune and test. Sweep the antenna with an analyzer, trim for resonance and re-check after rain, because wet ground and wet wire can shift it.

If you like to experiment before you cut wire, model the shape in antenna modeling software and compare an inverted L with a straight vertical of the same total length.

A Worked Example for 80 Meters

Suppose you want a CW and SSB antenna for 80 meters and you have a tree that holds a pulley at 12 metres. The quarter-wave figure for 3.6 MHz is about 19.8 metres, so a first cut of 21 metres of wire leaves a little to trim. Run 12 metres straight up the tree, which leaves roughly 9 metres for the horizontal part. Slope the horizontal wire gently away from the tree toward a lower support, keeping it well clear of branches and metal. Lay out at least a dozen radials from the base, each as long as the space allows, and bond them together at a plate under the feed point.

Sweep the antenna with an analyzer. If resonance is below your target frequency, the wire is too long, and you shorten it a little at a time at the far end. If it is above, add wire. After each change, check the result before cutting again, and make final adjustments after a spell of dry and wet weather so that you know how the antenna behaves in both. The same method scales to 160 meters, with roughly twice the wire and much more demanding supports.

The T Variation and Other Options

If you have supports at both ends of a long span, a T-shaped top load puts the feed point under the centre of the horizontal wire. The encyclopedia entry notes that the T version is omnidirectional while the inverted L is weakly directional. If height is the only thing you lack, a loading coil or a longer horizontal wire can compensate, but both reduce efficiency compared with extra vertical height, so use them as a last resort.

Receiving on the Low Bands

A transmitting antenna that works well is not always a good receiving antenna. The inverted L picks up local noise like any vertical, and low-band stations often add a separate receiving antenna to hear weak DX. Our guide to low band receive antennas describes Beverage and loop options that complement a vertical for transmitting.

Safety

• High RF voltage. The far end of a quarter-wave wire carries high voltage, and the feed point deserves respect at higher power. Keep both out of reach, and never touch the wire or the radial junction while transmitting.
• Keep it away from power lines. Plan the route so that a falling wire or mast cannot reach a power cable.
• Mark the radials. Wires at ground level are a trip hazard. Bury them shallowly or mark them clearly.
• Protect against lightning. Disconnect the coax when the station is not in use and use a proper entrance panel and ground.
• Respect exposure limits. A high-power antenna near living areas needs an exposure check.

Common Mistakes

• Skimping on radials. A poor ground system can turn power into heat in the soil.
• Making the vertical section too short. Height in the vertical part matters more than length in the horizontal part.
• Forgetting to trim. Cut long, and shorten in small steps.
• Running the horizontal wire too close to metal or to the house. Nearby conductors detune the antenna and absorb power.
• Ignoring common-mode current. A choke at the base protects the station from RF.

The Bottom Line

The inverted L is one of the best answers to the low-band space problem. It uses the height you can reach for the vertical radiator, bends the remainder of the wire into a top load and relies on a good ground system to do the real work. Aim for as much vertical wire as your support allows, build as many radials as you can, measure the match before you transmit and add common-mode protection. With patience, a simple wire antenna can give a modest station a real voice on 160 and 80 meters.

Frequently Asked Questions

How long should an inverted L antenna be?

The total wire length should be close to a quarter wavelength, which is about 39 metres on 160 meters and about 20 metres on 80 meters. Start longer than needed and trim it with an antenna analyzer.

Is an inverted L better than a dipole on 160 meters?

For long-distance work it often is, because the vertical section produces a lower take-off angle than a low horizontal dipole. A dipole needs significant height on 160 meters to perform well.

How many radials does an inverted L need?

There is no single number. More radials give lower loss, and many moderate-length radials work better than a few long ones. Read about radial systems for verticals and use as many as practical.

Can I feed an inverted L with coax?

Yes. Feed it at the base between the vertical wire and the radial system, ideally with a matching network or tuner at the base and a choke on the coax to keep common-mode current out of the shack.

Can I use one inverted L on several bands?

You can, with a tuner at the base. Resonance changes by band, and the feed point impedance can be very high on some bands, so expect more loss and plan for a good matching network.

Is the inverted L dangerous?

It carries high RF voltage at the ends, so keep the wire and the feed point out of reach, and treat it like any other transmitting antenna. Keep it away from power lines and ground it properly against lightning.