yup to the above things phage, Basically depending on where a nuke is set off determines what kind of damage it does, ie physical damage with some irradiation, irradiation only (but over a wider area than in the first case), EMP with little to no irradiation being the 3 "basic" ways a nuke can be used. basically correctly placed you could turn the entire world back to the dark ages with 12 well placed nukes. This being said military systems are built with this threat in mind. Meaning core electronics are either too deep to be effected or hardened to that kind of attack(primarily by using a different waffer type, its also MUCH more expensive) The real issue behind EMP attacks(or for instance an M class solar flare-this has been discussed before here btw
) is the infrastructure damage to things like commercial transportation and the power grid(primarily the transformers) which would leave the country at a stand still. while the technology exists to mitigate this it is not even close to widely deployed, or in some instances (such as non computerized diesel trucks) is being moved away from. As well for a society like america that is heavily industrialized this sort of attack is much worse on the civilian base than it would be in say china(or africa). basically an EMP attack is probably the single greatest threat to a nation like america that nothing is being done about.
Also as a note the same sort of thing that the amplification of an EMP is working off of is also used by radio waves(radiation!) to broadcast signals OTH depending on the frequency/atmospheric conditions the signal can be "bounced" off different layers, and even amplified.
One final note: the effects of our atmosphere to amplify signals is was not "new" information, what was "new" was the fact that we didnt realize nuclear devices had an EMP property to them, because in all of our ground/low altitude tests the primary fireball extends far further than the electromagnetic field generated. Leaving no trace/data behind to point to it. Anyway depending on atmospheric conditions at the time of detonation, regardless of yield of the device it can have either a larger, or smaller impact depending on the conditions present. Anyway their is just gobs of information about this out their on the interwbez if you want to learn more.
edit: i cant stop myself....
a great deal of hardened electronic devices(much like a nuclear hardened defense point) really just means that it can withstand a brief (single event) point of attack(or in the case of say a bunker a brief overpressurization), it is not like our satellites that have to withstand higher radiation over the course of years. Which is where things like m class or greater solar flares become an even greater danger, as its not a "brief" event. Meaning a good deal of EMP hardened technology would still fry as that kind of electromagnetic event can last several minutes(or possibly hours, but i dont believe their is any confirmation for that length of time, minutes their is however).
