The NK sats haven't emitted a peep since launch and are at the perfect altitude for a textbook emp pop. There's also the rumour that NK bought super emp tech from Russia and China.
It is arguable if they are at the perfect altitude, they are around 500 km alt (varies +/- about 30 km). The perfect altitude must be matched with the technology of the device used, what is the "perfect" alt for one sized device is not so much for a different sized device.
Now 320 miles is a really nice zone for EMP, assuming you have a device of correct yield. A large enough one at that alt would have a footprint covering much of the contiguous US. However a relatively low yield device, say on the order of 10x the size NK has yet actually detonated, would actually be hampered at that altitude, and would have a more effective footprint (not larger, but higher intensity) at a good bit lower alt.
Would Russia or China sell NK a tailored EMP device in the 1 MT or larger range? This is not 1991, Russia is not that hard up for hard currency.
As I type this KMS 3-2 just passed over the Russian heartland. Its next two orbits will take it over China. Such a weapon could easily be used by NK against China or Russia, and there would be nothing those nations could do to stop it. Providing a tailored EMP device small enough to fit on an NK rocket would be as dangerous to China or Russia as it would be to us. ANd NK has demonstrated that it will not be controlled by external nations.
Could NK have built a 1 MT or larger device themselves? Nothing they have done so far, no test, indicates they are anywhere near ready for that. And if they can, after the limited success they have had so far, could it fit on a sat they could lift to orbit? The KMS 3-2 is 1.6 meters, by 0.6 meters, by 0.7 meters, and is estimated to weigh about 100 kg. That has to hold whatever they want it to hold (such as a weapon) and all the TM and control stuff. We could build one to fit in that footprint, but we could not for the first 15 or so years of the most ambitious and public nuclear weapons development program seen so far. It took us about 7 years, and more than 30 successful tests, after our first test to get to our first multi-stage device, and more than 1 MT. And that device would hardly fit in a delivery truck, let alone a 100 kG payload rocket.
I see no indication, at all, that NK is at about the same level of weapons development as the US was at in 1960. They have had 5 tests, one fizzle at about 0.7 kt, the next 4 ranged from about 5 to about 25 kt. It was claimed, by NK, that the last one was of a correct size to be mounted on a missile / rocket. At the time of that test both the KMS 3-2 and the KMS 4 were already in orbit. Their demonstrated weapons tech as of the last launch was on the order of 20 kt.
At the altitude of the KMS birds 20 kt, or even several times that, is just about a firecracker.
Am I worried that they will get there? You bet, if not stopped or if they don't change their mind it is almost assured they will. But not yet, and probably not for a few more years. I think they need to pop a right size weapon in test before I start worrying about them maybe getting one to orbit.
T!