Because of the small bandwidth of the band, and the extremely narrow bandwidth of the antennas used, it is impractical to transmit audio signals (AM or FM radiotelephony). A typical AM radio signal with a bandwidth of 10 kHz would occupy one third of the VLF band. More significantly, it would be difficult to transmit any distance because it would require an antenna with 100 times the bandwidth of current VLF antennas, which due to the Chu-Harrington limit would be enormous in size. Therefore only text data can be transmitted, at low bit rates. In military networks frequency shift keying (FSK) modulation is used to transmit radioteletype data using 5 bit ITA2 or 8 bit ASCII character codes. A small frequency shift of 30-50 hertz is used due to the small bandwidth of the antenna.