Effective height (G.B.)
Of a linear vertical antenna less than a quarter-wave-length long, the length of a hypothetical vertical radiator, with its lower end at ground level which gives rise to the same radiation field at the same distance in the horizontal plane as the antenna, and which carries a current which is uniform in phase at all points along its length and of uniform amplitude equal to that of the maximum current in the antenna.
Reference: N.T.G. (modified)
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
centre of gravity
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM