Electromagnetic education can be greatly enhanced by providing students with a practical hands-on project that helps illustrate the different theoretical concepts covered. This paper introduces a unique build-a-radar course for this purpose, and is offered online for free in a self-paced massively open online format. The site can be accessed at https://llx.mit.edu, and provides students with an understanding of radar through the use of pre-recorded video lectures, review questions and associated reference materials. This course also contains a detailed set of instructions to guide students through the radar construction using a hardware kit that is also available online. Together, these combined offerings present a novel teaching tool for all students interested in radar and electromagnetics as a whole.