The DF Tractor Exhibit

During the early 1900s, the Army operated from mobile as well as fixed installations. The museum displays a picture of a mobile U.S. direction finding truck, or "tractor" in the terminology of the time. The truck had a DF antenna, which was turned by hand from the inside. By measuring the angle of entry and the skip of a signal coming in and bouncing off the ionosphere, an operator could pinpoint the distance the radio wave had travelled - rather advanced for 1918.