EMP weapons are NOT what you think that they are.
Merely detonating a nuke at altitude will not generate a huge EMP. To get that, one needs to design the warhead from the start to produce a massive EMP. Without getting too specific, this involves coupling the explosion to the Earth's magnetic field.
Don't worry about an Iranian EMP weapon. If Iran gets nukes, they will be used directly against cities in Israel and the USA.