Data transmission method and apparatus by period shift keying (TSK)

Apparatus for transmitting and receiving a period shift keyed data stream comprises a data processor such as a microprocessor which may control the generation of the waveform as well as the determination of the bit values of an incoming signal. When the data to be transmitted comprises a plurality of data values, each data value is represented by a different predetermined frequency. Further, each data value is represented by the transmission of the predetermined frequency for a predetermined transitionary interval plus one cycle or period. One portion of the transitionary interval precedes and the remaining portion follows the one cycle. For example, the data value may be represented by a three cycle burst of frequency such that, in determining the represented data value, two cycles of transitionary interval are detected but ignored and the central cycle of the three cycle burst is timed for determining the data value by edge detection techniques. Consequently, transitionary influences caused by changes in frequency do not adversely affect data value determination.