[Celerity]

No, an EMP will affect everything the same. It provides the spark that shorts out the microelectronics.

So on or off, the affect is the same.

An EMP isn’t guaranteed to destroy everything. It usually takes a few - when we’re talking about high-altitude explosions. A HERF or directed EMP device is highly effective... but the EMP That we are mostly talking about is a side-effect of detonations.

[Cobra64]

I should have kept my 1963 Ford Galaxie 500. No electronics. Just points and a rotor.

[txhurl]

Something tells me those sats are about to be dragged off - jetted off - to 1000mi above Earth’s surface.

[txhurl]

Is EMP only line-of-sight destructive? What if there was, say, a huge limestone hill between you and the burst?

[cynwoody]

No, an EMP will affect everything the same. It provides the spark that shorts out the microelectronics.

The last time the experiment was tried was 9 July 1962. Google Starfish Prime.

A 1.4mt warhead was exploded 250 miles above Johnston Island. Here's how it looked from Honolulu, 900 miles away:

The resulting EMP knocked out 300 street lights, set off numerous burglar alarms, and damaged a microwave link.

Back then, everything was discrete components. Most radios used vacuum tubes. Transistor radios were new and were classified by how many transistors they had (these days, I carry around a few billion in my pocket). Ted Hoff wouldn't invent the microprocessor until about 1969.

There has never been a proper atmospheric test using modern electronics. The only reason Starfish Prime took place was that the Soviets had reneged on an earlier ban on above-ground tests.