Traditional astronomy has focused on properties of the steady-state universe. Recent discoveries of strong, isolated radio pulses have, however, invigorated interest in transient phenomena. These radio transient events are rare, necessitating long observing times to give reasonable statistics. The National Aeronautics and Space Administration/Jet Propulsion Laboratory (NASA/JPL) Deep Space Network (DSN) tracks spacecraft continuously with several large antennas having low system noise temperature. The DSN also returns substantial predetection bandwidth from the antennas (400 MHz at X-band), currently processing only a fraction of that band for spacecraft tracking. This unused wideband capability is ideal for study of the radio transient sky. Here we describe and show initial performance results of a prototype receiver to search for such transients. This prototype is implemented as a firmware change in an operational DSN tracking receiver and can thus run in parallel with operational spacecraft tracks using existing spare receiver hardware. An operational version of this system could be deployed throughout the DSN to acquire data over extended periods and substantially improve the statistics of rare radio transient events.