Method of decoding data content of F2F and phase shift encoded data streams

In a decoder apparatus having logic means for comparing signal indications from a demodulator and also having at least two alternative decode value tables called states in which data contents may be interpreted in accordance with said indications from said demodulator, a method of decoding the data contents of F2F or two phase shift encoded data streams which have been demodulated in a demodulator to extract the characteristic 1F and 2F frequency pulses contained in such codes and between which pulses said demodulator has performed measurements and comparisons to characterize the intervals of time or distance contained between each pair of like polarity pulses as being equal to 1T, 1.5T, or 2T, where T is the nominal minimum distance or time normally occurring between two 1F pulses in said codes, said decoder also being provided with an indication of the type of code to be decoded and with the indications of the results of said interval characterization from said demodulator, the method of selecting a decoding state in said decoder and decoding said data contents in accordance with said interval indications comprising steps performed in said decoder of:

• controlling the decoding state of said decoder in accordance with said interval indication received from said demodulator for the two most recently received like polarity pulses in said encoded stream of data;
• selecting a set of possible data contents for the portion of said code stream encompassed by said two most recently received like polarity pulses in accordance with said decoding state of said decoder;
• and
• selecting and outputing the particular data content from said set of possible data contents in said state in accordance with said interval indication, thereby decoding the portion of said code lying between said two last received like polarity pulses.