I am working on a system that warns pilots when they are seen by another radar. Radar works by sending out radio frequency energy and then looking for reflections. Rather than transmitting continuously, most modern radars transmit a series of pulses. In the simplest case, the pulses from a given radar are evenly spaced in time. However, more complicated patterns also exist. When our system is looking for radars, it may see several simultaneously. When this happens, the pulses become intermixed. So our system then has a series of pulses which came from various radars that it must sort out. The goal is to form a train of pulses for each radar. That is, the system must take a single train of pulses and sort it into several trains, one for each radar present. Solving this pulse sorting problem is a fundamental step toward making the system workable.