Category Archives: world war II

Acoustic Mirrors: How to Find Planes without RADAR

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A lot of science museums and parks feature something called an acoustic mirror. The one at Houston’s Discovery Green park is called the listening vessels. [Doug Hollis] created two acoustic mirrors 70 feet apart, pointing at each other. If you stand or sit near one of the vessels, you can hear a whisper from someone near the other vessel. The limestone installations (see right) are concave and focus sound like a parabolic mirror will focus light.

Just a science curiosity, right? Maybe today, but not always. The story of these devices runs through World War II and is an object …read more

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Retrotechtacular: Hallicrafters Goes To War

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When the USA entered World War Two, they lacked a powerful mobile communications unit. To plug this gap they engaged Hallicrafters, prewar manufacturers of amateur radio transmitters and receivers, who adapted and ruggedized one of their existing products for the application.
The resulting transmitter was something of a success, with production running into many thousands of units. Hallicrafters were justifiably proud of it, so commissioned a short two-part film on its development which is the subject of this article.
The transmitter itself was a very high quality device for the era, but even with the film’s brief insight into operating

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