In Quadrature Phase Shift Keying (QFSK), there are four different phases, each representing a 2-bit symbol. It uses four phases (45, 135, 225 and 315) that are 90-degrees apart for four different 2-bit symbols 00, 10, 01 and 11. The frequency is same for all carrier waveforms. Figure 1 shows QPSK modulation of a digital signal.

Figure 1: Quadrature phase shift keying modulation

At the end of this experiment, students are encouraged to establish correspondence between the data bits and phases in the QPSK modulated signal. Students are also encouraged to observe lissajous patterns on the oscilloscope and sketch them in the manual.