Altitude is important. Given the right vehicle and the right device, the whole country could go in one shot.
Good analysis.
The equipment used to monitor atomic testing was protected from EMP by the use of Faraday Cages. It is a relatively simple way of shielding sensitive electronics. Much more about this and good info on doing this to your home and other items can be found at http://www.unitedstatesaction.com/emp_and_faraday_cages.htm
The time to do it is NOW.
I am having my terrorists use two EMP Bombs in the novel I am trying to write (actually completed, just going through the re-writes). EMP’s make fine small scale attack weapons. No where near what is being portrayed.
It would take a massive nuclear attack to affect the whole country. That is, an all out attack by a nuclear superpower. If are your going through all that trouble, you might as use the bombs correctly, closer to the ground and as a weapon of mass destruction.
Tubes/triodes/ vacuum tubes have ALWAYS been resistant to EMP, moreso than solid state transistors and printed circuits. I have read some recent work (from modeling and small scale testing) that indicate modern ASICs and even consumer automotive electronics might survive and EMP.
The weak point are the long lines of the power grid and general unshielded electronics that control it.
Your diesel tractor might indeed start and run quite well. But where do you get the next 50 gallon drum for the farm?
A US without electrical power collapses rapidly.
EMP *IS* a wide area effect, but it is also line of sight. A 50,000’ detonation would not do the trick. You gotta be higher up. But indeed the line of sight effect would span most of a continent. Sure the inverse square rule applies, but with nuclear devices you have power to spare.
Dismiss EMP and its societal effects at your own risk.
Even typing the letters E-M-P just shorted out all of Boston.
Don't play with that EMP.
Altitude is important. Given the right vehicle and the right device, the whole country could go in one shot.
A nuclear weapon exploded at an altitude of 30 mi or greater will produce three distinct types of EMP.
The first type induces voltages in conducting segments of all lengths, principally affecting microelectronics via breakdown of semiconductor junctions or the thin insulating layers of transistors, which are damaged by 10s of volts or less. Most vacuum tubes are undamaged by such “low” voltages.
The third type induces large overcurrents in very long stretches (100s of miles) of conductors, principally powerlines and communication cables,
both open air and buried a few feet or less. This type destroys electric power transmission equipment and communications hubs.
The second type, similar to lightning, is both “local” to the weapon and less damaging than the other two types.
A nuclear weapon as small as 50 kT exploded 300 mi above the central plains of the US is a grave danger since its “footprint” for the first and third types of EMP effects covers all of the continental US and most of Canada and Mexico.
To protect your electronic gear from Type 1, place it in a aluminum foil-lined box and disconnect it from any objects outside the box.
To protect your home against type 3, disconnect it from all external electric (grid) power lines and communication cables.
Obviously, defending yourself from high altitude EMP (aka HEMP) requires major changes to your way of life—living self-sufficiently in a solar-powered metal box.
As I understand it, 50,000 feet would not be high enough to induce a massively destructive EMP event. You need a lot more altitude so that when the neutrons from the detonation hit the top of the atmosphere it induces what’s known as the “Compton Effect” which basically fires a massive EMP straight down at the ground.
As I understand it, the Compton Effect was first verified as a result of some of the first atmospheric weapons tests out in the Nevada desert, when a significant portion of the Las Vegas electrical grid was fried.
Tubes are fragile is a different way than micro electronic circuits are today. You can generate electricity by passing a coil of wire through a magnetic field. Conversely, if you generate a massive electro-magnetic field around anything that acts like a coil, such as an integrated circuit board, the power surge instantly fries the whole board.
Recall the speculation about the Toyota gas pedal problems?? One of the things that is being looked at very closely, is what happens when you drive a Toyota car computer underneath an overhead high tension line. Those lines do in fact generate a powerful electro-magnetic field, and may very well be perfectly capable of zapping an electronic device if you pass through it in just the right way.
You actually meant "A quarter as strong at twice the distance...", right?