DIY Airplane Detector
May 1942 Popular Science

Homemade Plane Detector

RF Cafe - May 1942 Popular Science Cover

During World War II, Americans, Britains, Frenchmen, and other civilians were seriously engaged in helping to defend their homeland. Those who were not in the military gathered bottles, tin cans, tires, and clothing to use in the war effort. Others volunteered at the Red Cross, veterans' hospitals, and USO offices. Some stood guard at their nation's seashores and land borders, both as armed sentries and as troop and aircraft spotters. As part of the civil defense effort, listening devices were built to help detect the sound of approaching airplanes.

In patriotic tradition, magazines like Popular Science published many articles to assist the population contribute. Here is a plan for a "Homemade Plane Detector." It used a horn "antenna" that fed into a 3-stage tube-based (1H5GT) amplifier + 1G4G headset driver circuit. You could build and power one today with a couple 1.5 V batteries - oh, and a 90 V and a 135 V battery.

Johanson Technology Prototyping Kit - RF Cafe Website

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a lady's voice announced "You've Got Mail" when a new message arrived...