A device utilizing pulse techniques has been built for automatic measurement of changes in radio wave travel times. The equipment uses a combination of amplitude, time, and frequency selection for discrimination against unwanted signals. The received signals from U. S. time standard station WWV are sampled at 1‐sec intervals to measure changes in the time of reception of the 1‐sec timing pulses transmitted by WWV. The changes in travel time can give information on the vertical velocity of a virtual reflection point in the ionosphere and other factors of interest in the study of the ionosphere.