History LEO(K): Prof. Jhr. Ir. J. L. W. C. Von Weiler: pioneer of Dutch radar developments

Prof. Jhr. Ir. J. L. W. C. Von Weiler:
pioneer of the Dutch radar developments

Prof. Von Weiler celebrated his seventieth birthday on August 13, 1972. That prompted an article in Roering about the role that Prof. dr. Von Weiler has played in the Dutch radar developments. Below follows a slightly edited version of that article.

Jhr. ir. J.L.W.C. von Weiler
Jhr. ir. J.L.W.C. von Weiler

After graduating in 1934 with Prof. dr. Elias, he joined the Laboratory for Physical Armourment (“Het Meetgebouw”) under the Dutch Ministry of War.

UKG transceiver

His first assignment was to develop a portable transceiver at the wavelength of 1.2 m in the UHF transmission band. The transceiver was intended for use in the Royal Netherlands Army (see UKG transceiver). The series production was taken on by the Nederlandse Seintoestellenfabriek (NSF) in Hilversum. These transceivers were used in the war days of 1940, including at the battle of the Grebbeberg. Propagation trials were conducted during the development of the transceiver in 1935 . During these experiments, it was noticed that there were strong fluctuations in transmission when a bird and later an aeroplane flew over the trajectory between the two transceivers. Interference phenomena, which grew bigger and slower, occurred until the aircraft had passed the transmission path. Would this phenomenon be caused by reflected radiation from the plane? To investigate this systematically, a route was set out between Scheveningen beach and Waalsdorp. The dunes shielded direct radiation. Arranged military aeroplane flights were carried out between Noordwijk and Hoek van Holland. Indeed, it turned out that there was a connection between the two transceivers due to reflected radiation by the aircraft. From this, Von Weiler came up with the idea to use these aircraft reflections for aircraft detection and determinating its distance. The idea of Radio Detection and Ranging (Radar) was thus born in the Netherlands at about the same time that the English and Americans started working on it independently.

VHF radio transceiver
VHF radio transceiver

The first Dutch radar device

In the period 1935 – 1940, a small group of employees worked under his leadership on the realisation of the electric distance meter. To prevent interference from the transmitter on the receiver, pulsed transmission was used. In the intervals between the transmitted pulses, one could listen to the radar reflections by targets via the receiver. The challenge was that if one wanted to use the same antenna during transmission and reception, the receiver had to be blocked during the time of the emitted pulse.  To address this challenge, Von Weiler used three coupled transmission lines, one to the transmitter, the second to the antenna, and the third to the receiver. When transmitting, only a small portion of power entered the receiver. He coupled the third line to the grid of the first tube of the receiver via a capacitor and large leaking resistor. The remainder of the transmit pulse caused the grid to be negatively biased, which lowered the space-charge causing the grid capacity to be lowered. This detuned the matching network, and only a non-destructive small part of the transmitting power was dissipated by the receiver. During the receive period, the energy mainly went to the receiver. All elements of a modern radar were already present in this first Dutch radar – the ‘electric listening device’.

Model of the "electric listening device" (radar view)
Model of the “electric listening device” (radar antenna side)
Model of the "electric listening device"
Model of the “electric listening device” (operator side)

Technical characteristics of the radar

  • Wavelength 70 cm / 425 MHz.
  • Antenna: a number of dipoles on a mesh reflector (mattress).
  • Transmit pulse duration of 3 microseconds.
  • Transmit power 1 kW (pulsed) from four “apple valves”.
  • Pulse repetition frequencies were 7.5 and 15 kHz. This corresponds to a maximum distance range of 20 resp. 10 km.
  • Miniature tubes were used in the receiver: so-called acorn tubes.
  • To make the pulse audible with headphones, the transmitted pulse was amplitude modulated at 1 kHz.
Apple valves
Apple valves (Western Electric TB 04/8)

Industrial production of the radar

The laboratory developed four prototypes of the electric listening device. The Ministry of War decided to start a serial production at N.S.F. in Hilversum. Ir. Max Staal was the liaison officer with industry. To complete his draft duties, he was detached at the Laboratory for Physical Armourment (‘Meetgebouw’). This series production did not start given the outbreak of war in May 1940.

One of the prototypes was installed in the Hertenkamp in The Hague during the May-days. German aircraft were tracked with this device. One device on the roof of the laboratory at Waalsdorp was deliberately demolished by the personnel. The remaining two disassembled units were shipped to England in time.

The War Period 1940 – 1945 in England

When the war broke out in May 1940, the Navy asked Von Weiler to move to England taking a radar device and the drawings with him. Ir. Gratema was also supposed to join him, but he fell ill at the last minute. His place was taken by Ir. Max Staal.
In Hoek van Holland an English destroyer was ready to pick up the English Military Attache Admiral Dickens. Because Hoek van Holland was on fire and unreachable, the admiral was picked up by a smaller ship at the harbour of Scheveningen. Von Weiler and Staal joined him with the drawings of the radar. In England there was a car ready for the admiral and his fellow travellers; identification papers were not asked.

In June 1940 Von Weiler arrived at the Admiralty Signal Establishment in Portsmouth. The English were somewhat surprised at the fact that radar had been developed in the Netherlands. But the two prototypes created by Ir. Piket shipped from IJmuiden were already in Plymouth and were made suitable as a distance metre to cooperate with the fire control of the 40 mm Bofors machine guns that the Royal Navy used on its new ships. An English designed antenna, a Yagi, was connected (see photos). These radars – Range & Detection Finder type 289 (RDF 289) – were installed on HMS “Isaac Sweers”. In September 1941 they sailed with it to Malta with Von Weiler on board.

Anti-aircraft radar of the HMS Isaac Sweers
Anti-aircraft radar of the HMS Isaac Sweers

 

The advanced Dutch RDF 289 on the HMS Isaac Sweers (front view)
The advanced Dutch RDF 289 on the HMS Isaac Sweers (front view)

 

The electric listening/RDF transceiver of the HMS Isaac Sweers
The electric listening/RDF transceiver of the HMS Isaac Sweers

In addition to these activities, Von Weiler contributed to an English 50 cm artillery radar, especially its antenna design. He reported to Mr Ross, the head of the department, who was engaged in anti-jamming techniques. In this group, he worked on the development of a pulse length discriminator, a differentiation circuit, and Moving Target Indication (MTI) using a mercury delay line. He has also investigated paralysis symptoms in a disturbed receiver. This paralysis could be mitigated by avoiding coupling capacitors and by using power supplies that could supply large currents.

Antenna of the 50 cm artillery radar
The antenna of the 50 cm artillery radar

All these techniques were put in the design of a 3 cm radar that was in production in Canada. War required a fast delivery, but the factory could not remove the receiver errors. Paralysis symptoms were experienced when using strong signals. After these symptoms were resolved at the laboratory in Portsmouth, the series production could start. These 3 cm radars have served well during the landings in the Pacific.

The period after the second world war 1946 – 1972

Until the end of 1945, Von Weiler worked in the experimental department of the Admiralty Signal Establishment (ASE) in Portsmouth. In January 1946 he was placed at the Scientific Research Office of the Naval Staff in The Hague. On September 1, 1946, he was appointed as Professor by Special Appointment in the Department of Electrons Technology at the Delft University of Technology, where he had been teaching since January 1946. He also was appointed chairman of a radar committee, set up by the Minister of Defence to draft a plan for radar development in the Netherlands.

In December 1946, he was put in charge of the Navy Radio Service’ Testing and Development department (B&O) in Oegstgeest. The Laboratory of Electronic Development of the Royal Netherlands Navy (LEO) originated from this department.

In April 1948, Prof. jhr. ir. J.L.W.C. von Weiler was appointed by the Minister of War as chairman of the national technical radar committee in which the Royal Netherlands Navy, the Royal Netherlands Army and the Air Forces (the Royal Netherlands Air Force was not yet an independent Armed Force) were represented. Its task was to review the potential market for radar and to prepare a set of recommendations. The recommendations had to be about how the Dutch market would be best served: own R&D and production of radar or to choose for licensing of foreign equipment. On May 31, 1948), the committee came up with the recommendation for radar R&D and production in the Netherlands, with as core facilities the Physics Laboratory in The Hague, the LEO (later LEOK) in Oegstgeest, and Philips in Eindhoven.
As such he was a stimulator of a Netherlands radar industry. Standardisation of the equipment for the Netherlands Armed Forces was one of the work items. The final plan has had a great stimulating impact on the Netherlands industry in general and especially on the radar industry. The plan led to the design, development, and production of a number of search, acquisition, and tracking radars manufactured by Hollandse Signaalapparaten (nowadays Thales Nederland) and Philips Telecommunication Industry (PTI) Huizen.

On 7 June 1949, the Netherlands Royal Navy ordered the Navy Radio Service and the TNO Physics Laboratory in The Hague to develop in cooperation a long-range air warning radar (LW-radar) in the 25-cm/L-band. The radar had to be installed on board of the Navy ships under development. The prototype of the radar had to be ready in time for series production, in order to install the LW-radar simultaneously with the other radar systems. Just at the time of the order, the L-band magnetron type 5J26 became available on the market.

The 5J26 magnetron
The 5J26 magnetron (500-600 kW, 0.25% duty cycle, 1.2-1.4 GHz)

The work on the transmitter and receiver was carried out at Oegstgeest while the antenna development took place at the Physics Laboratory. The LW-radar system had to be built from scratch because a lot of components were not available on the market yet and had to be designed and engineered at the laboratory. The LW-radar had the interest of the Air Force as well. In an early stage, the industry became involved which led to the production of the LW-radar by Philips Telecommunication Industry and Hollandse Signaalapparaten. This LW-01 radar has been the start of a very successful series of LW-radars in use with the Netherlands Navy.

On June 25, 1955, the Laboratory for Electronic Developments for the Armed Forces (LEOK) was established by ministerial order of the Minister for War and the Minister of the Navy. The LEOK works for the three armed forces. The Professor was appointed as the director of the LEOK until he became a pensioner in 1967.

Prof. dr. Von Weiler has promoted the radar developments in the Netherlands in various ways:

  • by participating in the training of electrical engineers in Delft.
    Through his lectures, he aroused the interest of the students in the technique in cm waves, which are used in the radar;
  • by conducting discussions in collaboration with the Navy’s scientific research office to create an own Dutch radar industry. The discussions led to new types of artillery and warning radars on the post-war cruisers and fighters. The radar equipment made by the Dutch Industry (PTI and HSA) included the GA, KA, ZW, VI, DA, and LW radars in the 3 cm, 10 cm and 25 cm bands. Versions of the VI, DA, and LW radars were made fit for use by the Royal Netherlands Air Force. A 3 cm anti-aircraft radar was produced for the Royal Netherlands Army;
  • by LEOK, where he – as director – was the inspiring and stimulating leader for his employees. The LEOK developed equipment, researched new techniques, provided advice by the development of specifications, and carried out prototype inspections on industrial equipment.

Some highlights of the LEOK laboratory program were:

  • The laboratory model of the LW radar developed at the LEOK. In addition to the Royal Navy, this radar is also used by the Australian and Swedish Navy.
  • Development of specifications, performing measurements, and acceptance testing of the ER-438 radar for the Royal Netherlands Air Force. The ER-438 was developed and manufactured at C.S.F. in Paris.
  • Carrying out the same work for the 3D-radar of the Royal Navy, which was developed and made by HSA. The LEOK has played a large part in the development of the measurement method and accuracy measurements of distance, azimuth, and elevation. The LEOK developed and created a 3D-radar simulator that could inject 30 synthetic targets into the radar. The target tracks could be built and modified by the user.
  • Developing special receiver circuits and signal processing to visualise the target signals under difficult conditions of large land, sea, and rain reflections (clutter) and deliberate hostile disturbances (jamming).
  • Familiarizing the Armed Forces with intentional failure of the radar. For this purpose, the LEOK developed and built jammers that can be carried by aeroplanes. They interfere with one’s own radars. In this way, radar operators could be taught on how to use their anti-interference options.

In 1967, Prof. dr. Von Weiler retired as director of the LEOK. He was succeeded by Ir. F. J. van Hutten. Prof. dr. Von Weiler commemorated his 25-year Professorship by Special Appointment with the Symposium Electronic Navigation in Delft. This symposium was attended by nearly 200 friends and colleagues, many of whom had attended and graduated from him. On September 1, 1972, Prof. Von Weiler ended his professorship.

 
Source: ir. R. A. Kasper, Roering, May 1972.