[Hypervigilant]

I'm no expert, but the EMP from a nuke detonated at altitude is composed of three components (E1,E2,E3). The EMP is the result of interaction between gamma rays and the earth's atmosphere. Also, EMP interacts with the ionosphere. The result is damage to everything within line-of-sight of the detonation.

A blast at 300 kilometers would have a line-of-sight footprint of???

[BobS]

It depends upon pulse width, and peak pulse power level. I suspect a couple of thousand watts from 300 miles max from megaton value bombs. It radiates spherically from the source with power loss similar to 1/x^2. x is the distance of one point to another along a path from the source. Power is inversely proportional to distance. Then you must figure in effective killing power. What is that value? Assume you you have one single high energy pulse that is a squarewave of some sort. You have ONE wavelength and only ONE.

SO, you use D = 2 * d^2 / lambda.

D = best distance to disable electronics

d = cross-section of the target

lambda = the wavelength of your high-energy squarewave.

Now, this is just in free space without considering a bunch of other variables, but you have to start somewhere before you go out to buy your cigarettes and whatever nourishment of your choice.

It would be nice to know the pulse width and peak pulse power at the source before going further. And the height of the source. You have to define max and min limits composed of temperature, pressure, humidity that are part of absorption (attenuation) or reflection.

This is not a DC discharge as in lightning. This is RF power and all the microwave equations apply. If you know electrical relationships and physical-dimentional relationships and a moderate amount of calculus, look up microwave measurements and it will all fall into place for you. I've done this for 20 years and love making expensive things work! And I'm outdoors half the time like a little boy still!