Vertical Antenna Radials: How Many, How Long, and Where
A vertical is one of the easiest HF antennas to put up and one of the easiest to get wrong. The vertical element gets all the attention, but the vertical antenna radials decide how much of your transmitter power turns into radiated signal and how much heats the soil. Two operators can install the same vertical on the same band and get very different results purely because of what lies underneath it.
This guide explains why a vertical needs radials, how ground-mounted and elevated radial systems differ, how many to install, how long they should be, and how to check the result. It deliberately avoids specific numbers that depend on the antenna, soil and band. Use the manufacturer’s documentation and your own measurements for those details, and treat the advice here as a framework for making sensible decisions.
Why a Vertical Needs Radials
A quarter-wave vertical is only half an antenna. The vertical element is one half, and the other half is a mirror image supplied by the ground plane under it. If that ground plane is poor, the antenna behaves as if half of it were missing. You can read a general description of this arrangement in the ground plane antenna overview.
Return current and ground loss
Current flowing up the vertical must return to the transmitter, and it does so through the ground or through radial wires. When it flows through lossy soil, the resistance of the earth dissipates part of your power as heat. Radials give the return current a low-resistance path above or on the ground, which reduces loss and raises efficiency. The result is a stronger signal for the same transmitter power.
Radials also shape the match
The radial system affects the feed-point impedance. A poor ground shows up as a higher resistance, which can make the SWR look better than it should. This is a classic trap: a low SWR on a vertical with few radials can simply mean that a large share of the power is being wasted in the soil. For background on why SWR alone can mislead, read what an SWR meter tells you and what it hides.
Ground-Mounted Versus Elevated Radials
There are two main ways to build a radial system, and they behave differently.
Radials on or in the ground
Wires laid on the surface or buried shallowly interact strongly with the soil. Because the soil is part of the return path, a larger number of wires is needed to reduce loss. The wire length is less critical, and the system is forgiving of variation, but performance increases steadily as you add more wires, with diminishing returns after a point.
Elevated radials
Radials raised well above the ground behave more like the conductors of a resonant counterpoise. They couple less to the soil, so far fewer are needed, but their length matters: they are usually cut close to a quarter wavelength for the band in use. Elevated systems are typical for antennas mounted on roofs, poles or towers, and for portable use where you cannot bury wire.
| Radial type | Wires needed | Length | Best for | Drawback |
|---|---|---|---|---|
| Ground-laid or buried | Many | Not critical; longer is generally better | Permanent garden installations | Lots of wire and effort |
| Elevated resonant | Few per band | Cut for each band | Roof, pole and portable installs | Needs a set for each band |
| Mixed system | Moderate | Varies | Multiband gardens with limited space | Harder to tune predictably |
| Counterpoise on a roof | Few | Resonant | Apartments and flat roofs | Common-mode current risk |
How Many Radials Do You Need?
The honest answer is that it depends on the soil, the antenna and how much loss you accept. More radials always reduce ground loss, but the improvement per wire shrinks as the system grows. A small number improves things significantly over none; a larger number improves them further; and beyond that the gains become small. Good practice is to install as many as you can reasonably manage, spread evenly around the base.
Rather than chase a magic number, think in terms of loss budget. If you operate QRP or on a weak-signal band, every decibel counts and a bigger radial field pays off. If you operate casually on a busy band with a strong signal, a smaller system may be enough. Modelling software can estimate the difference; our beginner-focused guide to antenna modeling with EZNEC and 4nec2 shows how to compare radial configurations before cutting any wire.
Poor soil, good soil and salt water
Soil conductivity varies widely. Wet, rich soil conducts better than dry sand or rock, so the same radial field performs differently in different places. A vertical near salt water can perform very well because the sea is an excellent ground plane, and this is why coastal verticals are a common choice for DX. If your soil is poor, more wires or an elevated system usually pays off more than in good soil.
Radial Length and Layout
For ground-laid systems, length is not critical, and longer wires generally help until you run out of space. You can vary the length of individual radials to fit the garden. For elevated resonant radials, cut them close to the length appropriate for the band, and trim in small steps while checking the feed-point impedance.
Spreading them evenly
Spread the wires evenly around the base to keep the pattern symmetrical. If space is limited, it is better to make the radials of different lengths and lay them where they fit than to leave out an entire side of the antenna. Connect all radials at a common point near the base with a solid electrical bond, ideally soldered or clamped with corrosion-resistant hardware.
Practical materials
Ordinary insulated hookup wire works for many installations. Use wire that resists corrosion and mechanical damage, and secure it with pegs so that people and animals cannot trip on it. Bury or cover surface wires as soon as practical, and check the regulations for laying wire on shared land. In lawns, wire that has been laid on the surface for a season often sinks into the grass and becomes almost invisible.
Installing a Radial Field Step by Step
- Plan the layout. Sketch the vertical position and mark where each wire will run. Avoid paths where people walk.
- Cut the wires. Prepare them to a similar length, or the lengths that suit your space.
- Prepare the hub. Fix a metal plate or bonding point at the base of the antenna and solder or clamp each radial to it.
- Lay the radials. Spread them evenly, peg them down, and bury or cover them if possible.
- Connect the feed line. Attach the shield to the hub and the centre conductor to the base of the vertical element.
- Measure. Check SWR and impedance across the band, and compare against a run with fewer radials.
- Add more over time. A radial field can grow. Each added wire lowers the loss, so improve the system gradually.
Common-Mode Current and the Feed Line
A poor radial system can push return current onto the outside of the coax shield, which then acts as part of the antenna. This can cause noise, RF in the shack and an unpredictable pattern. A choke placed near the feed point helps, and a solid radial field reduces the problem at its source. See our discussion of common mode chokes and stopping RFI at the source, and check that your grounding follows the guidance in station grounding and lightning protection.
Remember that a radial system is not the same as a safety ground. Radials serve the radio-frequency return; electrical safety and lightning protection require their own connections and a plan for the whole station. Do not use one to replace the other.
Testing Whether Your Radials Are Enough
You can judge a radial system in several ways. Measuring the feed-point resistance before and after adding wires shows how the loss falls. An antenna analyzer or VNA makes this easy; if you own one, our guide to the NanoVNA antenna analyzer covers how to measure properly. On the air, compare signal reports with a nearby station over several days while you add radials. Reception-reporting maps can also show how strongly your signal is heard in different directions.
Also pay attention to noise. A vertical with a good radial field is often quieter on receive because it rejects some local noise, while a poor system may pick up more. If the noise drops as you add wires, that is a sign the system is doing its job.
Choosing a Vertical for Your Situation
If you have a garden, a ground-mounted vertical with a generous radial field is a robust, low-cost choice. If you live in an apartment or on a roof, an elevated vertical with a few resonant radials or a counterpoise is more realistic. If you operate portable, a tripod-mounted vertical with a small set of elevated radials packs into a bag and works well from the field. Our guide to your first HF antenna compares the vertical with the dipole and end-fed wire so you can decide which suits your site.
Whichever you choose, treat the radials as a full part of the antenna, not an accessory. Manufacturers of commercial verticals often supply a limited number of radials, and results improve when you add more. Read their recommendations, and refer to independent resources such as the ARRL for further reading on ground systems.
Multiband Verticals and Radial Trade-offs
Many commercial verticals cover several bands using traps, coils or a matching unit at the base. Each design makes compromises. A trapped vertical shortens the radiating element on lower bands, which lowers efficiency and narrows bandwidth, so the radial system matters even more. A vertical fed through a remote tuner at the base relies on the radials to complete the circuit on every band, and a weak ground system will waste power on all of them.
If you plan to use several bands from a single vertical, budget more effort for radials rather than less. Use the manufacturer’s recommended layout as a minimum, and add wires when you can. Keep notes of the measured impedance on each band so that you can see which band benefits most from an extra wire. A small change in one band may be barely noticeable in another, and that pattern tells you where to spend your time.
The Bottom Line
A vertical is only as good as the ground system beneath it. Use many radials when they lie on or in the soil, fewer resonant radials when they are elevated, and connect them solidly at a common point. Do not trust a low SWR as proof of efficiency, add radials over time, and measure the difference. A little effort under the antenna pays back with a stronger signal on every contact.
Frequently Asked Questions
Why does a vertical antenna need radials?
The radials provide the return path for current and act as the ground plane half of the antenna. Without them, the current flows through lossy soil and part of your power is wasted as heat.
How many radials should I install?
As many as you can reasonably manage, spread evenly around the base. More wires always reduce loss, but with diminishing returns. Elevated resonant radials need far fewer than wires laid on the ground.
Do radials have to be a quarter wavelength long?
For ground-laid radials, exact length is not critical and longer generally helps. For elevated radials, the length is important and is normally cut close to a quarter wavelength for each band.
Should radials be buried or laid on the surface?
Either works. Buried or surface wires interact with the soil and need more wires, but they are forgiving. Cover or peg them so they are not a trip hazard.
Can a good SWR mean my radials are poor?
Yes. Ground loss adds resistance that can make the SWR look low even when a large share of power is being wasted. Measure feed-point resistance and compare reports to judge efficiency.
Is a radial system a lightning or safety ground?
No. Radials serve the radio-frequency return only. Lightning protection and electrical safety need their own bonding and ground connections.
What if I cannot install radials on the ground?
Use an elevated vertical with resonant radials, or a counterpoise. Add a common-mode choke near the feed point and check for RF on the coax shield.