This paper describes the initial development of the balanced transmission-line wave sensor. This sensor is being developed to address the need for a directional sensor when dealing with extrapolation issues at hybrid EMP simulators. A prototype sensor was designed and tested. It provided good performance with measured front/back ratios between 20 and 29 dB. This may be adequate for many applications. There are, however, many variables left to explore, and it may be possible to improve the front/back ratio with further work.