Radiation efficiency of horizontal VLF antennas connected to ground Radial field dependence: Transmitting dipole moment current . length = 1 Am  Background noise level above ground: 5 dBuV/m   red: vertical E-field in air, black: horizontal E-field in the ground, blue: H-field ( . 377 ohm) Vertical electrical antenna: Horizontal wire connected to average ground: Horizontal wire connected to very dry ground: Geometry of an earth-antenna: View from top View from side Equations: Complex wavenumber k in lossy medium:   Fields generated by a small electrical dipole:   Fields generated by a small magnetic dipole:   Skin depth:   Coupling c between vertical polarized surface wave and longitudinal electrical field:   (applicable if antenna length l > d and l > d) Mirror effects of the earth-air interface: In the air above the surface, the vertical (E-field) polarisation is doubled by the image antenna, whereas the horizontal polarization is short-circuited.  Beneath the surface, the air acts as a magnetic wall, suppressing vertical E-fields and currents.