Altitude and magnitude are key. The higher up it is, and the bigger yield it has, the worse the effect. We did several above ground and low altitude tests, and even then there was an EMP effect, but it gets worse the higher in the atmosphere you go.
I can understand the higher up, the more field of view and longer range, but still don’t get why emp wouldn’t of have an effect locally to NKs neighbors when tested not deep but near ground level as they did, if emp is really a threat? Also consider, way up, why cant a bomb wipe out the whole one side of the earth if it is so much of a threat at altitude? Because to view the whole side earth from one vantage point, an orbit really high is needed, and since intensity of radio waves falls off at an exponential rate ( inverse square of the distance) , at some point the emp is too far away. So then why at ground level emp had no effect his weekend and, a bomb Half Way to the moon has no effect, too far away, but a bomb at launch orbit can wipe out the whole US? Who figured that only launch orbits are not too close but not too far? Consider, the EMP damage reported, in Hawaii, decades ago, only a few things were effected, but cheap 1960s transistors were used in those days so ...where is the evidence today ? ... people just keep saying there is a threat ? I’m sure there is some, but how do really we know?