The following is a translated summary about an article regarding the Philips Obstacle Detector.
In 1935 Engineer C.H.J.A. Staal joined the team of Engineer K. Posthumus, inventor of the improved Dutch cavity magnetron, which operated at 40% efficiency and 50-cm wavelength. An improvement was made to 19 à 25cm at 10 Watt. Modulation frequency for the radar trials were set at 400 Hz. It was then a mission to find purposes for these inventions. Between Eindhoven and Tilburg and Eindhoven and and Nijmegen a link of 140cm and 25cm respectively were set up. Two wooden parabolae coated in metal paint were used for reflectors and a traversable metal plate of 1m² was used. The Koninklijke Marine was interested in these trials and perhaps inspired by the SS Normandie wanted to detect ships with this.
At airbase De Mok, Texel, on the stuifdijk (dust embankment) a pair of parabolae were placed in June-July 1937. Results were disappointing as constant reflections were measured. Attempts to solve this problem were in vain and in late August these tests were ended. In the discussions after the bad results van der Mark of the television group suggested using pulses. Staal supposed that the oversight of this in hindsight obvious solution was the result of tunnel vision and proved once more the value of bringing in outsiders to look at a project.
A local oscillator of around 1500 MHz (20cm) was used. For the display an oscilloscope, the A-scope, was used. The navy gave the team a wooden cabin at Wijk aan Zee and two cannons to use in tests. The parabolae were mounted on top of the barrels and tests in 1938 showed the ability to detect a 1 m² plate at 1000 m. A Z-class torpedo boat was then detected at 3000 m.
Based on the promising results a test installation was ordered and installed in the first two months of 1940 at around 1½ km north of Wijk aan Zee. Two tests were scheduled of which the former on the 6th of March with an auxiliary minesweeper failed due to communication failures. The second, on 20th March, the tests with Jan van Brakel succeeded with echos being visible up to 3200 m. A test with Sumatra was considered.
The current model used only one parabola separated by a horizontal bulkhead. This model was shown to two French officers in May 1939. Back in the NatLab of Philips a new model was being developed. This one mounted on a searchlight mount to allow vertical elevation. In March-April this one was ready. However due to dissatisfaction with the performance of the magnetron a new model from May 1940, the HF dubbeltriode DZ 19, was used. Which increased the wavelength back to 40cm.
Due to the high demand for altitude meters the development of the obstacle-detector was put off until October 1940 when the demobilised engineer Zonneveld was tasked with the resumption. In the summer of 1941 new tests were held on the roof of the factory in Strijp, under the eyes of an alert but unaware German soldier of the air warning service.
'Radar: een vergeten stuk geschiedenis'. Ongepubliceerd artikel van ir. R. van der Hulst en prof.ir. E. Goldbohm over de ontwikkeling van de radar bij de NV Philips' Gloeilampenfabrieken te Eindhoven vóór de Tweede Wereldoorlog. Met marginaal commentaar van Erik de Vries.
Nationaal Archief, Den Haag, E.K. de Vries, nummer toegang 2.21.327, inventarisnummer 264
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