In high power VLF transmitters, to increase the allowable data rate, a special form of FSK called minimum shift keying (MSK) is used. This is required due to the high of the antenna. The huge capacitively-loaded antenna and loading coil form a high tuned circuit, which stores oscillating electrical energy. The of large VLF antennas is typically over 200; this means the antenna stores far more energy (200 times as much) than is supplied or radiated in any single cycle of the transmitter current. The energy is stored alternately as electrostatic energy in the topload and ground system, and magnetic energy in the vertical wires and loading coil. VLF antennas typically operate "voltage-limited", with the voltage on the antenna close to the limit that the insulation will stand, so they will not tolerate any abrupt change in the voltage or current from the transmitter without arcing or other insulation problems. As described below, MSK is able to modulate the transmitted wave at higher data rates without causing voltage spikes on the antenna.