"In operation the elevated terminal of a Tesla-coil transmitter
functions as one plate of a capacitor. In opposition to this
terminal is every other electrically conducting body to which it is
electrically connected, including the earth and the receiver's
elevated terminal. The transmitter's elevated terminal serves two
purposes. First, it acts as a charge reservoir in opposition to the
earth's surface in the immediate vicinity of the
transmitter. Second, it is one of two capacitor plates, the other
plate being the elevated terminal of the receiving facility. In an
ultra-high-power Tesla-coil RF transmission-reception system these
two capacitor plates act as high voltage discharge terminals for the
formation of capacitively coupled discharge plasma with
interconnection taking place through the upper level atmosphere."