Where you think they would target?
Don’t need the h-bomb, its not the explosion you need but the burst of energy. I’ve read some sources which indicate relatively small bombs would be adequate if detonated high enough. As you go higher the line of sight extends. The pulse will go out 3000-4000 miles. There are also ways of engineering the weapons to produce a larger pulse.
Most electronics today are extremely susceptible to EMP. I used to doubt this was really a threat so I researched it fairly extensively.
Here is a sobering report - http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-htm/fs41elecpuls.htm
“A 1.4 Megaton bomb launched about 250 miles above Kansas would destroy most of the electronics that were not protected in the entire Continental United States. “
Equally spaced, 100,000- 200,000 feet above North America.
Assume freighter launch from open sea off coast or body of water. Positional accuracy is not that important for EMP attack. Target:
1) Philadelphia - hits northeast rather hard, is accessible from Atlantic.
2) Southern California - much of west coast, accessible from Pacific
3) Chicago - gets midwest, accessible from Great Lakes
Depending on yields and altitudes, this may leave out Seattle, Texas, and Gulf Coast. But it covers the bulk of the population and where they live. Military targets are ignored as they are generally hardened. Most of electric grid is down for a while.
Just a SWAG based on an atlas...
“Three H-bombs. Fission bombs won’t have the boost.”
A single 10kt bomb would do the trick, properly placed. There is very little difference between the EMP from a 10kt and a 100kt.
I’m not convinced we’d go back to the stone age, but it would be ugly.