An experimental study on the general characteristics of the three different optical arrangements, namely, local-oscillator heterodyne, differential heterodyne, and symmetric heterodyne, is given. Both rotating Mylar disk and steady-state rotating flow are used to generate a uniform particle velocity or flow velocity. The power spectrum of the photoelectric current is obtained both in real time by a spectrum analyzer and numerically by a digital computer. An fm-demodulator is also used to obtain the instantaneous velocity. The S/N, stability, optimum particle concentration, and optimum receiving optics of these three optical arrangements are obtained. Their relative merit and their comparisons with theoretical results are also discussed.