A method for detecting encoded digital data from a substantially sinusoidal waveform, the encoded digital data having one of a first value and a second value at selected phase angles .theta..sub.n comprises generating the waveform having an amplitude Y defined by a first function at phase angles lying outside of regions having a range .DELTA..theta. beginning at each phase angle .theta..sub.n, said first function being Y=sin .theta.; generating the waveform having an amplitude Y defined by the first function at phase angles lying inside the regions having a range of .DELTA..theta. beginning at each phase angle .theta..sub.n where data of the first value is to be encoded; and generating the waveform having an amplitude Y defined by a second function at phase angles lying inside the regions having a range of .DELTA..theta. associated with each phase angle .theta..sub.n where data of the second value is to be encoded, the second function being different from Y=sin .theta., the detection including deriving sync pulses from minima and maxima of the substantially sinusoidal waveform to frame data words.