Phase Shift Keying (PSK) is a technique of digital modulation that uses variations in phase to transmit the information.

Binary Phase Shift Keying (BPSK) uses two signal phases (0 degrees and 180 degrees). For each bit of the incoming signal, the waveform of output signal is determined according to the state of the preceding bit. If the input signal state stays the same (0 or 1), then the phase of the waveform does not change. If the input signal changes from 0 to 1 or from 1 to 0, then the phase of output waveform changes by 180 degrees. BPSK is also called biphase modulation or phase reversal keying. Figure 1 shows BPSK modulation of a digital signal.

Figure 1: Binary phase shift keying modulation

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