1.5 Frequency-shift keying (FSK)

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 a relatively high frequency (three cycles per time period) and a relatively low frequency (one and a half cycles per time period). Periods in which the frequency is high correspond to a 1, and periods in which the frequency is low correspond to a 0. Thus the overall pattern of the sinusoid is as follows: high frequency for one time period, low frequency for three time periods, high frequency for two time periods, low frequency for one time period, high frequency for one time period, low frequency for two time periods.