Radio Communication: Electro-Magnetic Pulse research (1970 – 1993)
Electromagnetic Pulse Facilities (1970 – 1993)
Background
An electromagnetic pulse or EMP is a very intense impulse of electromagnetic energy that can occur during a nuclear explosion. In 1962, EMP was discovered after a nuclear test at 400 km altitude, about 800 km from Hawaii. The effects on July 9, 1962, in Honolulu were described in a magazine: “The quiet predawn in Honolulu in 1961 was shattered by the simultaneous pealing of hundreds of burglar alarms. At the same instant, circuit breakers on the power lines started blowing like popcorn“.
Only sometime later, when no cause was found, a correlation was made with the nuclear test at a large distance. The defects and failures that occurred were caused by EMP and were comparable effects of a short-range lightning strike. EMP is, therefore, a phenomenon in which the strengths of the electric and magnetic fields increase to very high values in less than one hundred millionths of a second. As a result, for example, a peak voltage of 25,000 V occurs in a rod antenna of a portable radio, as a result of which transistors in the radio are fried. Electrical systems and installations with long wires and cables will likely be disrupted or are destroyed, such as electrical power stations, refineries with process controls, communication centres, computers and the like. The treacherous aspect is that EMP effects may occur in an area with a radius of more than 1,000 km when a nuclear weapon explodes high in or just outside the atmosphere. Even when this happens far outside the Dutch territory, it still can be dangerous.
Since 1970, TNO Waalsdorp has therefore been using EMP simulators and computer programs to investigate exactly what the effects of EMP are on electronic systems and what countermeasures can be taken. In summary, an EMP simulator requires a high electrical voltage, very short rise times and very high frequencies. Therefore, such a simulator consists of a high-voltage pulse generator connected to a so-called flat-plate transmission line, which is terminated at the end with an ohmic load R = Z0 where Z0 is the characteristic impedance of the transmission line.
EMIS-1, EMIS-2 and EMIS-3
At first, a small EMP simulator was built called EMIS-l with the nickname “Piggybank”. Its internal size was about 0.8 x 0.8 x 1 meter; the external cube size was 2 * 2* 2 metres. Only small devices up to 50 x 50 x 50 cm could be tested in EMIS-1 for their EMP sensitivity up to 50 kV/m.
Later, a large 60-meter simulator was built behind the laboratory at Waalsdorp: EMIS-2. EMIS-2 allowed the testing of entire systems with dimensions up to 3 x 8 x 25 meters. To simulate an EMP in EMIS-2, a capacitor battery was charged up to 500,000 V and then discharged into the transmission line using a very fast switch (spark gap). In less than 5 nanoseconds, a current of about 5,000 Ampères would flow into the transmission line. Between the “plates” of the transmission line, the generated impulse-shaped electromagnetic field then corresponds to a nuclear EMP. The strength of the generated field could be set because it was necessary to know at which EMP level system defects would occur. The highest field strength that could be generated in the test volume of EMIS-2 was 80 kV/m.
At the start of an EMP test, the power flows in cables, antennas and circuits were first measured using special measuring equipment. The possibly vulnerable parts could then be identified from the measurements and from studying the schematics of the equipment. If the EMP test showed that defects occurred, TNO investigated what kind of protection measures could be taken.
EMIS-3 was an even larger, mobile EMP simulator that was installed at the military airfield Ypenburg in 1982. EMIS-3 allowed the testing of aircraft, ships, and complete communication centres for their sensitivity to EMP. In 1983, a horizontal emitter for EMIS-3 was installed and a transmission line that could be used to test accommodations and aircraft at threat level was completed. In the next years, the system was continuously used to test the equipment of the Armed Forces. In 1987 experiments started with the current induction generator with which, at EMP threat level, currents could be induced in cables of communication systems.
In July 1992, a completely renewed pulse generator for the EMIS-3 was transported to the EMIS installation at Ypenburg. This simulator met the newest, 1990, NATO test requirements. On 14 October 1992, all acceptance tests were completed and the installation became operational. Aside from EMIS-3 at Ypenburg, only an EMP test installation existed in the USA that was capable of generating a comparable pulse, albeit with some limitations.
It is worth mentioning that the EMIS-2 antenna became completely disabled when the Cheetah CA1 PRTL anti-aircraft tank underwent EMP tests. The then unit commander sent us his story in 2024:
“As a conscripted soldier, I became a unit commander with the Dutch 43rd Armoured Anti-aircraft Artillery. I was stationed in Havelte. Sometime in 1983, we got a request from TNO to participate in EMP testing of the detection and guidance systems of the PRTL. I was assigned that task together with two soldiers. That was nice: all three of us lived in the The Hague area. We could work on the Waalsdorpervlakte for a week or two and be at home in the evening.
The PRTL was transported with a LoLo (DAF YT-616 with a Notoboom semi-trailer) to the Frederikkazerne. The next day we drove the tank to the Waalsdorpervlakte with an escort of military motorcycles. A short ride, but quite an experience in itself of course. The PRTL was a ‘beast of a tank’. I think we had to drive up and down every day because the PRTL was not allowed to remain on the EMIS-2 installation for the night. We also did some maintenance work at the barracks according to schedule.
At TNO’s EMIS-2 location, the PRTL was placed under the antenna wires. After a general explanation of what we were going to do, we were instructed for each of the tests to turn on or position the PRTL equipment in a certain way: radar on – radar off, tracking radar activated or not, turret hatch open or closed, guns high or low. A whole series of test positions passed.
We set the desired configuration for a test and then deboarded the PRTL before an EMP took place. After each pulse, a series of tests were performed. External equipment was then connected to the PRTL and the TNO technicians completed a test program. Sometimes we were needed for assistance, sometimes not.
A nice activity for us as conscript soldiers: not too busy, and it was nice and quiet at the location.
The PRTL crew took turns. The driver had his tasks, but with my fellow soldier, we took turns in setting the PRTL configuration.
One night it rained. The next morning it was my turn to prepare the PRTL for the tests. The tracking radar would be activated that morning. However, next to the EMIS-2 installation was a large roll of mesh. The meshes of the mesh contained rainwater, making the entire roll radar-reflective. The tracking radar responded to that, immediately followed by the guns. However, the roll of mesh was well within the minimum distance to track an aircraft. The tower couldn’t turn that close to follow an airplane given the angular velocities.
The PRTL’s systems then automatically made a vertical search. During that search, the tracking radar found the EMP antenna wires strung above the PRTL. Since they were also wet and reflective, the gun barrels automatically assumed an almost vertical position. The antenna wires, however, were also much closer than the minimum tracking distance. With the gun barrels raised, the ends of the barrels stuck between the antenna wires and the thick wooden beams that kept those wires separated. The PRTL tower then automatically made a 360-degree search.
With that circular search of the tower and the gun barrels, the antenna wires and wooden beams rotated around the barrels like a coil. Both the wires and the beams broke. I was slightly injured because part of one of the beams landed on my head. Of course, the crash also made a lot of noise. My reflex was to return the PRTL to its idle position: tracking radar retracted, gun barrels horizontal and the turret set to zero degrees of rotation. There was one button to cause that. Towards that rest position, the tower rotated almost 180 degrees. That movement combined with the downward-moving gun barrels caused the entire EMIS-2 antenna installation to be pulled downwards. Remember, all these actions happened in a few seconds.
Chaos was everywhere on the test site. I got off the PRTL with a bloody head. It was not immediately clear that I was only slightly injured. I suffered a cut and a bump on my head. In a short time, the EMIS-2 test site was overrun by many TNO people and military. Later, two military police officers arrived to record my statement. ‘Was I to blame?’ I refused to answer questions by the military police without an officer present with knowledge of radar systems in general and the PRTL in particular. After some time, a colonel from the nearby Frederikkazerne arrived with knowledge of the matter. In the meantime, a medic was able to treat my head wounds. In the presence of the colonel, I told the story above. I did make no mistakes with the PRTL operation. The PRTL system responded as programmed and was supposed to work. The PRTL’s automatic actions were also confirmed by the colonel. The problem was the wet roll of mesh next to the EMP test installation. I never heard anything about the incident again.
There was a chance that the PRTL barrels were twisted or no longer straight due to the incident. That is why we painted two red rings on each barrel of the PRTL at the Frederikkazerne to prevent shots from being fired with the system. That was, unfortunately, the end of our time in The Hague. When we returned to Havelte with the red markings on the gun barrels of the PRTL, we attracted a lot of attention. The incident story had already preceded us. Together with colleagues of the Corps of Engineers, we dismantled the cannons. They were returned to the factory. We then drove for some time a PRTL without guns. That was a bit weird.“
