An alphanumeric system, method, and apparatus includes a parallel tone transmitter, a parallel tone receiver, each having a conventional telephone frequency type of A and B or parallel tone oscillators, and a splitter of tones from the receiver. An A tone will last for an interval long enough to assure protection against response to spurious tones such as voice signals, but may change frequency during the character period. When the A tone is constant during a complete character period, the B tone will not last as long as the A tone, but will change frequency after a set interval, for an A-B-B sequential, alphanumeric code, during the character period for each character. Alternatively, both the A and B tones are changed to provide an A-A-B-B sequential code for each character. The audio tones employed are standard, avoid intermodulation error, and the system maintains voice protection, while increasing the number of alphanumeric characters for a period of fixed length.