I think, in order for an EMP to have a wide reaching impact, the nuke would need to be 3-15x higher up than the balloon is said to be (at 100k ft). Although, the very northern part of the American continent, just east of the middle point, it is said to be the optimal place for an EMP to have the widest effective reach. For a bomb small enough to be carried by a balloon, which also has some form of satellite looking array, the bomb would have be designed specifically to output higher frequency gamma rays that interact with the atmosphere, but my understanding is that the lower down in the atmosphere that you get the less effective the EMP will be because of gamma ray radiation attenuation by ordinary atmosphere (versus something much higher that would be able to interact with the magnetic field and ionosphere before ever encountering ordinary air molecules and water vapor).
I think, in order for an EMP to have a wide reaching impact, the nuke would need to be 3-15x higher up than the balloon is said to be (at 100k ft). Although, the very northern part of the American continent, just east of the middle point, it is said to be the optimal place for an EMP to have the widest effective reach. For a bomb small enough to be carried by a balloon, which also has some form of satellite looking array, the bomb would have be designed specifically to output higher frequency gamma rays that interact with the atmosphere, but my understanding is that the lower down in the atmosphere that you get the less effective the EMP will be because of gamma ray radiation attenuation by ordinary atmosphere (versus something much higher that would be able to interact with the magnetic field and ionosphere before ever encountering ordinary air molecules and water vapor).