An rf pulse system is described for investigating progressive distortion of finite amplitude waves propagating in liquids. The system employs pulses short enough to avoid reflections but long enough to approach continuous wave conditions. A 25‐Mc quartz crystal backed by fused quartz serves as a nonresonant receiver for the first few harmonics of the 2.58‐Mc working frequency. Harmonic content is determined by Fourier analysis of waveform photographs, or by use of a heterodyne analyzer having bandwidth adequate to pass the pulse envelope. For an initially sinusoidal wave of 3.0 or 6.0 atm pressure amplitude in water, curves are shown tracing the decay of the fundamental and the growth and decay of harmonics through the fourth, to a propagation distance of 40 cm. Results are in good agreement with published theory within the region of convergence of the latter.