Before revision: The large VLF antennas used for high-power transmitters usually have bandwidths of only 50–100 hertz , and when transmitting frequency-shift keying (FSK), the usual mode, the resonant frequency of the antenna must sometimes be dynamically shifted with the modulation, between the two FSK frequencies .
After revision: The large VLF antennas used for high-power transmitters usually have bandwidths of only 50–100 hertz .