This diagram shows a line graph. The X or horizontal axis is labelled as time, measured in seconds. The Y or vertical axis is labelled as voltage, measured in volts. Time periods are represented on the diagram by a series of equidistant dotted vertical lines. Each time period is labelled with a 1 or a 0, in the sequence 1 0 0 0 1 1 0 1 0 0 from left to right.

Here a sinusoidal signal of amplitude 1 volt is shown varying between two different phases, one in which the waveform rises to a peak at the beginning of the time period (the first phase), and one in which it descends to a trough at the beginning (the second phase). Periods in which the waveform has the first phase correspond to a 1, and periods in which the waveform has the second phase correspond to a 0. The sinusoid switches between the two phases as follows: first phase for one time period, second phase for three time periods, first phase for two time periods, second phase for one time period, first phase for one time period, second phase for two time periods.

1.6 Phase-shift keying (PSK)