RADAR – In 1904!

Electrical Tester – 2 January 2019

Author: Keith Wilson, Electrical Engineer

Most engineers and many non-engineers will have at least a vague idea about the beginnings of radar. It was invented in Britain during the Second World War, wasn’t it? And didn’t it help the Allies to win the war? The name Watson-Watt may even come to mind as one of the leading pioneers. Well, all of this is true but it’s not quite the full story. In fact, the course of history could have been very different because a form of radar was invented and demonstrated in Germany in 1904!

The fascinating story is fully told in an article written by V J Phillips and published in the July 1978 issue of the British magazine, Wireless World. This article is, in turn, based on an item published in The Electrical Magazine (London) in 1904.

The inventor was Christian Hülsmeyer of Düsseldorf, and he called his invention the Telemobiloscope. The Electrical Magazine notes that he demonstrated his apparatus to North German Lloyd (a major maritime insurer), before going on to say: “The new invention is based on the principles of wireless telegraphy and is intended for viewing ships and metallic objects at sea. [No aircraft in 1904, of course!] In wireless telegraphy, the transmitter and receiver are used separately on different ships, but both are on the same ship with the Telemobiloscope. The electric waves, not being able to reach directly the receiver, must be reflected by metallic objects on the sea (that is ships) so as to reach the receiver on a broken path. The advantage afforded by this invention is mainly that ships fitted with the transmitter and receiver will be able to view any other ship devoid of these apparatus.” That’s a pretty reasonable description of how radar works, isn’t it?

It seems incredible that this system could be made to work given the technology available in 1904 – the Telemobiloscope used a spark transmitter (essentially an electric arc connected to an aerial) and a coherer receiver.

A coherer is a glass tube with metal filings loosely contained between two metal plugs. Normally, the electrical resistance between the plugs is high, but if the device is exposed to RF energy (radio waves) the metal filings stick together (cohere) and the resistance falls to a much lower value. The device must then be reset by tapping it to disturb the filings so that it is ready to respond to the next burst of radio waves.

Unfortunately, this means that coherers are inherently sensitive to mechanical vibration so, as V J Phillips notes in his article, they were far from ideal for use on board a ship! Conversely, they were very insensitive to RF, so a lot of reflected energy from the “radar” target would have been needed to get any response at all.

Given these limitations, did the system actually work? It seems so, because The Electrical Magazine concludes its piece by saying, “Experiments made so far on small instruments designed for shorter distances [probably less than a kilometre in this context] have given every satisfaction.” British patent 13,170 was granted in 1904 for the original apparatus, and British patent 25,608 later in the same year for “certain improvements.”

Fortunately for the Allies in the Second World War, the Telemobiloscope appears to have received little further attention, most probably because of the limitations of the technology used. That left the field clear for Watson-Watt and his team to develop the first practical radar system, which had such an enormous influence on the course of the war. But, as we’ve seen, it could so easily have been the Germans, not the Allies, who had the advantage of radar in that conflict.


Fig 1 and Fig 2: These two diagrams in the image are taken from the patent application. The top one shows the general principle, and the bottom one (presumably!) shows the arrangement of the apparatus.