For a horizontal antenna over average ground, ground reflection focuses energy at an angle set by height: the first lobe peaks near θ = arcsin(λ / 4h). Low antennas fire straight up; high antennas fire at the horizon.
- Below ~¼ λ — NVIS: most energy goes nearly straight up and comes back down within a few hundred miles. Great for regional 80/40m nets; hopeless for DX.
- Around ½ λ: the classic compromise — a ~25–30° lobe that works both regional and multi-hop DX.
- 1 λ and up: the main lobe drops under 15° — real DX territory. This is why 20m works from a 35 ft wire but 80m doesn't.
- Verticals play by different rules (low takeoff regardless of height, but need a good ground system) — this page is for horizontal wires and yagis.
- Raising an antenna from 35 ft to 45 ft matters a lot on 40m and barely at all on 10m — spend tower money where the wavelength says it counts.