Illustration of Telemobiloscope

1904 Telemobiloscope

The book of science

Tom Sharp

Christian Hülsmeyer electromagnetism Illustration of Telemobiloscope


Heinrich Hertz had discovered that electromagnetic waves bounced off metallic objects. Christian Hülsmeyer used that idea to invent the telemobiloscope. A spark-gap transmitter and a rotating parabolic antenna detected the presence and the direction of a ship in the fog. Additional measurements and basic trigonometry determined an object’s distance. However, lacking tuning circuits, the telemobiloscope was confused by wireless devices on other ships.


Add control for the signal frequency. Add tuning for the receiver. Add amplification. Add slotted waveguide. Add parabolic dish for broadcasting and receiving. Add control of the signal polarization. Add Doppler analysis to detect movement. Add digital signal processing. Add chain of coastal stations. Add phased array radars.


I send out signals all the time, see if any bounce back, tell me what’s out there and how far away, whether it’s moving in my direction or farther away, whether to dodge or chase it. I send signals out in all directions, see if anyone responds. I gradually improve the signal and the signal processing. Yes, this has been a metaphor from the beginning. I’m just trying to see if you’re paying attention.

The telemobiloscope was a precursor to the first radar systems, which required further technical advances and were developed in secret by several nations before and during the Second World War.

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