Antennas significantly shorter than the fundamental resonant length of one-quarter of the wavelength (0.25formula_15, 90 electrical degrees) are called "electrically short" antennas. Electrically short antennas are efficient "radiators"; the gain of even a short antenna is very close to that of a quarter-wave antenna. However they cannot be "driven" efficiently due to their low radiation resistance. The radiation resistance of the antenna, the electrical resistance which represents power radiated as radio waves, which is around 25–37 ohms at one-quarter wavelength, decreases below one-quarter wavelength with the square of the ratio of mast height to wavelength. Other electrical resistances in the antenna system, the ohmic resistance of the mast and the buried ground system, are in series with the radiation resistance, and the transmitter power divides proportionally between them. As the radiation resistance decreases more of the transmitter power is dissipated as heat in these resistances, reducing the efficiency of the antenna. Masts shorter than 0.17formula_15 (60 electrical degrees) are seldom used. At this height, the radiation resistance is about 10 ohms, so the typical resistance of a buried ground system, 2 ohms, is about 20% of the radiation resistance, so below this height over 20% of the transmitter power is wasted in the ground system.