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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Steve Conner wrote ...
The problem with your circuit is the inductance of the "Gnd" path. It would work better if you did it like Lodge, with a spark gap between the cones. Creating a voltage difference slowly, and then discharging it suddenly, works just fine. You charge the cones to opposite DC voltages and then discharge them to each other.
No pulse forming network is necessary. The discharge of the spark gap kicks the antenna into resonance, and it functions as its own pulse forming network, perfectly matched to itself by definition. :)
Sandia Labs actually built a device like this to test EMP hardening of military equipment. Firing was a two-stage process. The cones were charged to opposite voltages by a bipolar Marx generator, and then discharged to each other through a pressurised gas gap in the middle.
Perhaps not quite as simple as Steve's description suggests:
Bumgardner MK, et al EMP SIMULATORS FOR MISSILES AND AIRPLANES
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
It can be that simple. I just found a paper on IEEE Xplore that describes pretty much what I just said. They used a SF6 gap for a higher breakdown voltage, filled the centre section of the bicone with ethylene glycol to increase the capacitance, and charged it with a Tesla coil instead of a Marx bank to simplify things.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Can't see any reason why not. A VDG makes a reasonable EMP generator in its own right, they have been known to destroy electronic gadgetry in the area. You're just giving it a better antenna.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
No, you need a spark gap between the two cones, and an inductor (or high voltage resistor, water resistor would do) from the top cone back to the bottom of the VDG.
Registered Member #518
Joined: Tue Feb 13 2007, 05:20AM
Location: New York
Posts: 168
I think you can make the same thing using an inductor without the cones... if you charge an inductor and discharge it it also creates a voltage difference between one end and the other....
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New HERF idea...
