In this paper, the characteristics of radio transmitter fingerprints will be examined by analyzing both the amplitude and phase information obtained from complex envelope recordings of transmitter turn-on transients. The interest in the analysis of such transients is related to the identification of malfunctioning or illegally operated radio transmitters in support of radio spectrum management practices. Of the 28 VHF radios considered in this study, many were found to produce fingerprints having uniquely distinctive features which could be used for identification purposes. Unfortunately, some of these radios were found to have fingerprints that were virtually indistinguishable from each other, making the identification process more difficult, if not impossible. Details of the equipment, analyses, and data collection procedures will be presented along with a discussion of the experimental results. The merits of this technique over others currently in use will also be presented. ¿ 2001 American Geophysical Union