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This 1942 black and white, partially animated film was produced by the U.S. Army Signal Corps (USASC) during in collaboration with the Chief of Air Corps explains “the creation and behavior of radio waves” and antennas during the WWII era (TRT: 10:47).
Opening title card: “Official War Department Training Film 1-474 Restricted” (0:06). A large radio tower extends high into the clouds. Title appears: “Radio Antennas” (0:19). A transparent dish atop a radio tower (0:37). A radio transmitter on the underside of an aircraft. Two more atop an airplane. A vertical antenna pole on a small plane (0:41). Three radio towers stand in an open field (0:49). A compass is held open near a wire. As the compass approaches the wire, the needle rotates (0:52). Animation: A series of concentric rings with clockwise arrows encircle a black pole and pulsate. Then again, with counter-clockwise arrows. Repeat alternation at higher speed (1:06). A clear rod picks up strips of paper using static electricity (1:29). Another animation illustrates a magnetic field and the forces of attraction around the rod (1:40). The concentric circles and the illustration of the rod (1:53). A diagram of a circuit with a battery, a condenser, and an open switch (2:11). Concentric circles appear around the circuit as the switch is closed. They disappear when the switch is opened. Then, the battery begins to rotate, alternating positive and negative polarity (2:23). The condenser emits waves from both poles (3:22). The condenser is enlarged within the diagram of the circuit to show detail of the wave shape (3:28). The condenser, centered, extends symmetrical waves across both sides of the screen. It rotates as the waves flash (3:36). An illustration of a high frequency generator. It sends out a series of broad waves at an accelerating pace (3:50). An illustration of a radio tower emits similar waves at high speed (4:52). Dissolve to pace the waves slowing. The space between waves is measured with text and an arrow, “wavelength.” Animation repeats with progressively shorter wavelengths (5:05). Title card: “Radio Waves in Space” (5:24). Animation shows a dotted line emitting from a radio tower skyward in a straight diagonal line, then again, reflecting or ricocheting off the ground (5:33). A wider view, showing the earth’s curvature, the word “ionosphere” appears above. Waves bounce off of it (5:53). A radio wave reflects off the earth’s atmosphere multiple times in a zig-zag pattern (6:19). Higher frequencies are visualized as not reflecting (6:59). Return to live-action footage of a radio tower with wide, horizontal antennae at its peak (7:21). Animation of a radio tower sending waves earthward, labeled “ground wave” (7:34). A wider view shows a tower (not to scale) broadcasting waves across the United States, encountering earth’s curvature (7:50). Another wave reflects above the U.S. and lands on the east coast (8:18). Text illustrates “skip distance” between waves (8:29). Multiple reflections (8:35). A map shows waves emanating from Cincinnati and spreading to St. Lous, Kansas City, Denver, with a “zone of silence” in between (8:46). Animation of radio tower waves going over a mountain and landing in a city (9:04). Again, missing the city. Ground waves reach the city (9:30). Two paths of waves converge and overlap (9:55). A lattice of overlapping and criss-crossing waves (10:07). The live-action radio tower returns (10:13). An air traffic control tower. Medium shot of a U.S. Consolidated B-32 Dominator bomber aircraft (10:22). An air traffic controller and the B-32 in full view among the clouds (10:24). Title card: “End of Training Film 1-474” with the seal of the Signal Corps (10:33).
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This film is part of the Periscope Film LLC archive, one of the largest historic military, transportation, and aviation stock footage collections in the USA. Entirely film backed, this material is available for licensing in 24p HD, 2k and 4k. For more information visit www.PeriscopeFilm.com