Most advice about HF antennas quietly assumes a couple of acres and some tall trees. If you have a 40-foot back garden, an HOA, or a third-floor apartment, that advice is useless — and the conclusion people draw, that they cannot work HF, is wrong.
Compromised antennas work. Stations on balconies work the world every day. What matters is understanding precisely what each compromise costs, so you choose the one that costs you least.
Start with the numbers
Two formulas cover most of what you need.
Half-wave dipole, total length in feet: 468 ÷ f(MHz)
Quarter-wave vertical, length in feet: 234 ÷ f(MHz)
| Band | Half-wave dipole | Quarter-wave vertical |
|---|---|---|
| 80 m (3.7) | 126 ft | 63 ft |
| 40 m (7.1) | 66 ft | 33 ft |
| 30 m (10.1) | 46 ft | 23 ft |
| 20 m (14.2) | 33 ft | 16.5 ft |
| 17 m (18.1) | 26 ft | 13 ft |
| 15 m (21.2) | 22 ft | 11 ft |
| 10 m (28.4) | 16.5 ft | 8 ft |
Cut a few percent long and trim — a wire is easy to shorten and annoying to lengthen.
Note what this table tells you immediately: 20 m and up fit almost anywhere. A full-size 20 m dipole is 33 feet. If your constraint is space rather than money, the high bands are wide open to you, and those are the DX bands anyway.
The honest comparison
Half-wave dipole — the baseline
Two quarter-wave legs, fed in the middle with coax. Cheap, efficient, and the thing every other antenna is measured against.
Costs you: length, two supports, and it is single-band unless you fan multiple pairs of wires off one feedpoint.
Do this if you can. Running it as an inverted V — apex at the highest point, ends sloping down — needs only one tall support, drops the feedpoint impedance conveniently close to 50 Ω, and gives up very little. It is the highest-performance-per-dollar antenna in amateur radio and it always will be.
End-fed half-wave (EFHW) — the small-lot default
The same half-wave of wire, but fed at one end through a 49:1 transformer. The end of a half-wave is a high-impedance point, and the transformer brings it near 50 Ω.
Gains you: the feedpoint is at one end, so you need one support and one anchor, and you can run it from a corner of the house to a single tree. It also works on harmonics — a 40 m EFHW is usable on 20, 15 and 10 m without a tuner.
Costs you: it needs the feedline as part of its counterpoise unless you deliberately stop it, which makes common-mode current the standard failure mode. Symptoms are RF in the shack, SWR that changes when you touch the radio, and USB devices dropping out on transmit.
Fit a common-mode choke at the transformer and a second one where the coax enters the building. Either a coil of coax through a stack of type-31 ferrite cores, or a purpose-built 1:1 current balun. Budget $30. This is not optional on an EFHW, and it converts the antenna from frustrating to excellent.
Vertical — when you have no height but some ground
A quarter-wave vertical against a ground system. Low take-off angle, which is genuinely good for DX, and it needs no horizontal span.
Costs you: radials, and people skip them. A ground-mounted vertical without a proper radial field is a resistor with an antenna attached — a significant fraction of your power heats the soil. Ground-mounted wants 16 to 32 radials minimum, as long as you can manage, laid on or just under the surface. They need not be resonant; more and longer is better.
An elevated vertical is far more forgiving: mount the base several feet up and use just two to four tuned radials sloping away, and you get most of the performance with a fraction of the wire. If you have a flat roof or a balcony rail, this is often the best answer available.
Verticals also hear more noise than horizontal antennas — they are omnidirectional and vertically polarised, which is exactly what most household electrical noise is.
Magnetic loop — the apartment answer
A small tuned loop, typically 3 to 4 feet across, with a high-voltage variable capacitor. Efficiency is far below a dipole, but “far below” still means real contacts.
Gains you: it is small, it works indoors, it is directional enough to null out a noise source by rotating it, and it is remarkably quiet on receive because it responds to the magnetic field component.
Costs you: money — a good commercial loop is $500 and up — and bandwidth. The Q is so high that retuning is needed every few kHz, which means a remote tuning motor. Power handling is limited by capacitor voltage.
If you live in an apartment and have been told HF is impossible, this is the antenna that proves otherwise.
Random wire with a 9:1 unun
As much wire as you can get up, into a 9:1 transformer, into coax, into a tuner. Add a counterpoise wire roughly the same length as the radiator.
Gains you: flexibility. Any length, any shape, all bands.
Costs you: efficiency you cannot easily predict, and it demands a tuner. Avoid lengths that are near a half wave on your favourite band — the feedpoint impedance goes very high and the match becomes lossy. It is a fine “get on the air this weekend” antenna and a poor permanent one.
Attic antennas
A dipole or loop in the attic space. Invisible, which for HOA situations is the whole point.
Costs you: several dB to building materials, and much more if there is foil-backed insulation or metal ductwork in the way — those can block you almost completely. Nearby house wiring couples in noise on receive and picks up RF on transmit, which is how you end up interfering with your own television.
An attic antenna sits a few feet from occupied rooms. Run an RF exposure evaluation for your power, band and distance — it is required, and in this configuration it is not a formality. In practice this usually means running lower power, which is an acceptable trade for being on the air at all.
Height, and why it dominates
For horizontal antennas, height above ground determines your take-off angle — where your energy goes in the vertical plane.
- At a quarter wavelength up, most energy goes nearly straight up. That is NVIS: excellent for regional contacts out to a few hundred miles, poor for DX.
- At a half wavelength up, the main lobe drops to a useful low angle and DX performance improves dramatically.
For 40 m, a half wavelength is 66 feet. Most of us are not getting there, and that is fine — but it explains why the same dipole behaves so differently at 20 ft and 40 ft.
Practical consequence: before spending money on a better antenna, spend effort raising the one you have. A dipole moved from 20 ft to 35 ft frequently outperforms a fancier antenna left low. The high bands help here too — a half wavelength on 20 m is only 33 ft, which is achievable in a great many gardens.
Get a NanoVNA
A NanoVNA costs about $50 and will tell you the actual resonant frequency, SWR across the whole band, and the complex impedance of your antenna. An SWR meter tells you “bad” — a VNA tells you which direction to trim and by how much.
It turns antenna work from guessing into measuring, and it is the best fifty dollars in the hobby. Measure at the feedpoint where you can, and remember that coax loss makes a bad antenna look better from the shack end.
If you are genuinely restricted
In rough order of how well they work:
- Attic dipole or loop for the highest band you can fit. 20 m fits in most attics.
- Balcony vertical with a couple of elevated radials, or a screwdriver antenna on a rail clamp.
- Magnetic loop indoors, rotated to null your worst noise source.
- A wire out a window to a tree or a fence post, on a 9:1 unun, at whatever angle you can get.
- Portable operating. This is not a consolation prize. Drive to a park, throw a wire in a tree, and run POTA — many restricted operators end up preferring it, with better antennas and no noise floor.
And regardless of antenna: fix your noise floor before you upgrade anything. Switching power supplies, LED bulbs, cheap phone chargers and solar inverters routinely raise the noise floor by 10–20 dB. Walk the house with a battery-powered receiver, turn breakers off one at a time, and find them. Removing a noise source is free gain on receive, and it is usually the single biggest improvement available to a small-lot station.
Next: Your First HF Station covers the radio and feedline side, and Reading Propagation explains which band to point all this at.