Click graph to change ground type
Permittivity Conductivity 81 5000 mS/m Salt water 80 1 Fresh water 20 30 Pastoral, low hills, rich soil 13 5 Pastoral, medium hills and forestation, heavy clay soil 10 2 Sandy, dry, flat, coastal 5 1 Cities, industrial areas 3 0.55 Desert
These graphs show forward gain for horizontal, vertical, and tilted orientation of a halfwave dipole for center heights between 3 and 50 feet. These are NEC-2 results using Sommerfeld-Norton ground for a 98 MHz circularly polarized signal arriving at a 1° elevation angle. The gain reference is a circularly polarized isotropic antenna in free space. The difference between the solid and dotted green curves is F/B for the tilted dipole.
Apply the curves to any antenna by adding its free-space gain in dBd to the Y axis. The model is for flat ground with a single specular reflection and no obstructions. Only general trends hold for irregular terrain where scattering at multiple points causes complex wave interference.