electromagnetic pulse experiments

GBPPR Electromagnetic Pulse Experiments -

Part 1

Project Overview

This article will discuss the construction of a very simple Electromagnetic Pulse(EMP) generator. This particular design won't be capable of destroying everycomputer in your neighborhood, but it will give the constructor a good overviewof the concepts which make up electromagnetic pulse warfare. It should benoted that you will be working with very dangerous voltages and currents onthis project. Muslims, Eurosavages, Digg kiddies - you will be immune tothis. People with brains may wish to exercise caution.

The EMP device described in this article will work as follows:

A surplus high-voltage DC power supply will be used to generate an outputvoltage between 3,000 and 4,000 volts. This high-voltage will then charge anold 8 µF, 3,000 VDC General Electric Pyranol capacitor (the "C") via a currentlimiting resistor. When the capacitor is fully charged, it will discharge via aspark gap. The spark gap circuit will be part of an inductive circuit (the "L")which, along with the capacitor, sets up a natural resonant frequency. Togenerate the actual emitted pulse, part of the LC-tank circuit will be made offine wire, a lightbulb filament in this case. Since the lightbulb filament can'thandle the high-current discharge from the pulse capacitor, it will be instantlyvaporized. This "exploding wire" will essentially be turned into anelectromagnetic pulse which is radiated from an impromptu parabolic dishantenna. That's the idea at least.

Since the resonant frequency of this particular EMP device is very low (20 kHzor so), it will actually do very little damage to any electronic devices in itspath. Most "real world" EMP generators aim for the UHF or microwave RFbands by using tuned mechanical cavities. The shorter wavelength ofmicrowave RF energy is ideal for being coupled into the circuit board traces inthe target electronic device. The resonant frequency of this generator can beincreased slighty by replacing the lightbulb with a long piece of small-gaugewire. Experiment with the length, composition, and diameter of the wire used.

An optional ferrite core transformer will also be described. When this ferritecore is placed over a power cord, or other similar exposed wire, theelectromagnetic pulse can be directly injected into the target system. This is amuch more efficient method than the "exploding wire" idea.

The most critical component in an EMP generator is the high-voltage pulsecapacitor. The ideal capacitor will be non-polarized and with a low internalinductance and resistance. The internal resistance inside the pulse capacitorwill determine how fast, and to what final level, it can discharge. Commerical

GBPPR Electromagnetic Pulse Experiments - Part 1 http://gbppr.dyndns.org/mil/emp/index.html

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pulse capacitors that are designed for this purpose are available, but their priceis usually out of range for the hobbyist. Search amateur radio swapfests for oldPolychlorinated Biphenyls (PCB) high-voltage capacitors. You can usually pickthem up for free due to their high cost of disposal. Just don't let the hippiesknow about them, or they'll try to tax amateur radio experimentersnext. Several capacitors can be banked together in parallel to increase theenergy output. You can also place low-voltage capacitors in series so they canhandle higher voltages.

EMP Block Diagrams

For more detailed information on EMP generators and construction informationon a similar design, refer the book Electronic Gadgets for the Evil Genius (ISBN0-07-142609-4) by Bob Iannini, or see http://www.amazing1.com.

Construction Notes & Pictures


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High-voltage power supply parts overview. The heart of the power supply is aGeneral Electric 9T63Y2065G12 DC Power Supply. Its maximum output voltageis approximately 12,000 VDC at around 1 mA. It takes a standard 120 VACinput. A variac will be used to control the power supply's final output voltageby controlling the input AC voltage. If a variac is not available, it is possible touse the low-voltage secondary winding from a standard AC transformer tocontrol the power supply's input AC voltage.

The other support components are an AC line filter, a Radio Shack metal-oxidevaristor, a panel-mount SO-239 RF connector, a green neon light, two fuseholders (one panel-mount), an AC outlet, two binding posts (with rubbergrommets), a solid-state relay, a surplus 0-120 VAC variac, a bunch of surplusferrite cores, and an old military radio surplus voltage transformer. This will beturned into an isolation transformer for feeding the variac. Everything will bemounted inside an old ammo box.


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And put it all together as so. The AC line filter and dual fuses are probablyoverkill, but they're a good idea when working with EMP devices. The isolationtransformer is used to isolate the variac from the AC mains in case the "hot"and "neutral" lines are reversed.


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Front panel rear view. After the input AC line filter, the "hot" voltage linepasses through a solid-state relay. This relay will allow the high-voltage powersupply to be remote controlled from a safe distance. The solid-state relay'sremote control is nothing more than a 9 volt battery and a switch.


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The isolation transformer is made by tapping a 110 VAC secondarywinding. You can often find these transformers, or the military surplus radiosthey're inside, quite cheap at amateur radio swapfests. Their secondarywindings can only handle a few milliamps of current though. There is a 100ohm resistor and 0.1 µF AC-rated capacitor on the isolation transformer'sprimary winding to act as a "spike snubber" circuit. The use of an isolationtransformer before the variac is not required, but highly recommended.

The power supply's high-voltage output is on the left via the binding posts. Thebinding posts are set inside rubber grommets to isolate them from the metalcase. The maximum voltage this entire setup can handle before arcing over isonly around 6,000 volts.


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Completed front panel view. Main AC input is via the outlet shown. TheSO-239 connector is for the remote control. The variac's knob and main inputfuse are on the right.


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Rear view showing the output high-voltage binding posts.

Parts for the remote control. All you need is a metal outlet box, a cover plate, aswitch (with guard), a panel-mount SO-239 connector, a 9 volt battery with asnap and holder, a panel-mount LED and 470 ohm resistor, a 0.01 µF capacitor,and assorted mounting hardware.


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Put it together like so. An extra ferrite bead was slipped over the control'spositive line.


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Overview of the completed remote control. Connect it to the high-voltagepower supply via a good length of RG-58 coax with PL-259 connectors on eachend.


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The spark gap will be made from two drilled and tapped steel mouseballs. Ideally, you'd want non-ferrous materials that are nickel or silver plated.

Flatten one side of the mouse ball with a grinder and drill an appropriate hole


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for the thread tap. On this project, the mouse ball for the "hot side" (capacitorside) will have a #12-24 tap. The other mouse ball will have a 1/4"-20 tap.

For the "cold side" of the spark gap, use 1/4" brass, bronze, or copperhardware. It will be mounted on a small piece of wood which is then attachedto the side of the pulse capacitor. The "inductive" elements are mounted to thespark gap via a standard copper ground lug. Use brass bolts with the head cutoff for the threaded brass rod. It's all kinda retarded, but it works.


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Completed spark gap assembly. The gap hasn't been set yet. The air gap willbe set at around 1 mm per 1,500 volts used. You can use a spark plug feelergauge to help set the initial gap width. The split washers and nuts secure themouse balls to their respective threads. The gap can then be further adjustedby turning the brass rod in and out, then tightening the securinghardware. The gap on this device was set to "spark" at around 3,500 VDC. Thisis slightly over the voltage rating on the pulse capacitor, but it should handleit. Be sure to fully discharge the pulse capacitor before adjusting the spark gapwidth.

The wooden spark gap holder is attached to the side of the pulse capacitorusing some two-part epoxy putty.


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The "exploding wire" holder will be made from an industrial heat lamp. Thesehave a nice porcelain lamp base and parabolic reflector.


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Rear view of the porcelain lamp base. This is what sets the maximum operatingvoltage on this EMP generator. This particular model lamp base could onlyhandle around 6,000 VDC before arcing over.


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Solder two pieces of #6 solid copper wire to the porcelain lamp base likeso. You may wish to add a little "Q-Dope" to prevent high-voltage arcingbetween the two wires.


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Next is the high-voltage input circuitry. The current limiting resistor(s) and RFchoke need to be mounted on little standoffs to prevent arcing. These aresecured to the side of the case with nylon hardware. Note the extra ferritebeads slipped over the incoming power lines. These, along with the 4700 pFbypass capacitor, help to suppress any "back-EMF" when the spark gapfires. The RF choke shown (red cylinder thing) is from an old switching powersupply. Its value is around 8.5 µH, which is probably too low for thisapplication. Oh well.

The current limiting resistor(s) should have a high-voltage rating. Lowerresistance values will charge the pulse capacitor faster, but this may stress yourhigh-voltage current source. The time (in seconds) it takes for the capacitor tocharge is approximately: t = C * V / I. Where C is the capacitor's value (Farads),V is the capacitor's charging voltage (Volts), and I is the capacitor's chargingcurrent (Amps).


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Make a securing bracket for the pulse capacitor from some 1-inch widealumimum bar stock, two pieces of 5/16" allthread, threaded couplers, andother assorted hardware. Drill two holes in the alumimum bar stock and placeit so it can sandwich the capacitor to the bottom of the case.


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Completed closeup picture. A large hole is cut into the front of the case and theporcelain lamp base is epoxied in place. The solid copper wires which make upthe inductive elements of the circuit are clamped into the grounding lugs whichattach to the "ground side" of the pulse capacitor and to the "cold side" of thespark gap. These wires will need to handle several hundreds (or eventhousands) of amps, so exercise solid construction practices when securingthem.


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Completed overview.

Parts for the direct coupling ferrite transformer core. This is a total hack, but itdoes appear to work quite well. The split ferrite (or powdered iron) cores are aswapfest grab, so start looking out for those! You'll also need a 2-prong AC


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plug, some smaller sized grounding lugs, and an AC socket to lamp screw-inadapter thingy.

Wire it all up as shown. You'll want to put a little hot glue on the AC plug tokeep the prongs from moving. Be sure the copper wire turns around the ferritecore are not shorted, or that they are so tightly wrapped they crush the brittleferrite material. Experiment with the number of turns needed, but you'll have ahard time getting more than three. Slip some vinyl tubing over the copper wirefor protection.


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Screw the coupling ferrite transformer assembly into the lamp base asshown. Secure the other half of the ferrite core with a plastic sliding-jawclamp.

This connection method didn't work out too well, as it was too heavy for thesmall lamp socket. You are better off just wiring the ferrite transformer directlyoff the spark gap.

To operate, just run your target's power, ground, Ethernet, etc. wire throughthe ferrite core and zap away! Try to wrap the target cable multiple timesthrough the ferrite core, if possible.

Be careful, as it is possible for the transformer's halves to shatter due to theinduced current in the ferrite material.


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Overview of the EMP generator and the high-voltage power supply connectedtogether. Note the metal-armored power cord on the high-voltage power supplyand the coaxial cable for the remote control. All the cables in the local areashould be shielded to protect them from the electromagnetic pulse.

Various different lightbulbs were tried, and they didn't do too much exceptexplode into little pieces. It looks like you'll need to have a pulse capacitoroutput in the hundreds of Joules to have any really significant results.

Another possible EMP option is to connect metal Slinkys to each side of thespark gap to act like antennas. This could help radiate the electromagneticpulse a little bit more.

Schematics / Block Diagrams

High-Voltage Power Supply Block Diagram

Notes / Links

Higher resolution pictures and the original project article are available inGBPPR 'Zine Issue #38

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Other Related GBPPR Projects:

GBPPR Electromagnetic Pulse Experiments - Part 2

GBPPR Electromagnetic Pulse Experiments - Part 3

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GBPPR HERF Device

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electromagnetic pulse experiments

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