[Rhodes]

Unfortunately for your purpose its all theory, no one has set off a 50M nuke 200 miles up to see what it would take to protect certain devices. I do know the idea drives the military nuts and policy changes when one theory gains favor. The foil suggestion has merit but again how do you test it. I say go cheap and sparingly concentrating only on devices you have for SHTF like radio and make sure you ground the home well.