Maybe you should visit a few prepper forums, this is a topic often discussed there
EMP is an often misunderstood effect. On one hand you have people who are unfamiliar that such a thing is possible and would say there is nothing to fear, and on the other you have people incorrectly assuming a single high level EMP device will kill all electronics in the US. The truth is someplace in the middle. Also, the results are VERY arguable, models show from extreme damage to every electronic device to moderate damage to a portion of the devices.
A HEMP (High-altitude Electro Magnetic Pulse) will effect a large are, a SREMP (Source Region Electromagnetic Pulse) will effect a specific region. The SREMP will be much more devastating to general electronics while the HEMP will be more effective against infrastructure.
Past studies have shown that a single HEMP detonated 250 miles above Kansas would have some impact on electronics across the entire continental US. While some low level electronics (radios, computers, the computer that runs your car, air traffic control systems, etc) closely centered under the device would be affected the majority of the impact across the rest of the nation would be felt to power distribution systems, telephones, data lines, etc.
In a simplified way you can look at it like this, the HEMP typically effects things connected to large area conductors. Large area conductors are things like the power grid, telephone lines, data lines (non-fiber), and large antennas. The larger the area the conductor covers the more current that will be generated. The current has to have someplace to go, and things connected to the conductors make a nice place for the current to go. So that a light bulb plugged into the AC socket in your house might be killed, but the spare light bulb in the kitchen drawer will not. The radio connected to a large external antenna might suffer a damaged front end (the closer to centered under the device the more likely), while the one not connected to anything and setting on the bench probably will not.
A good specific example of this would be the 250 mile altitude 1.4 MT nuclear test done above Johnston Island in 1962 (Starfish Prime, part of Operation Fishbowl). This test damaged infrastructure related hardware (street lights, telephone systems, etc) as far away as Hawaii (about 900 miles), but the impact was relatively minor, some street lights (about 300 total) needed to be replaced, fuses blew in a few houses, and a telephone microwave link needed to be repaired. There is no reported damage to ham radio gear or similar equipment, despite many of them being in actual use at the time of the EMP. Nor have I heard or read that any radio gear was damaged on ships and islands closer to the device.
Because of variations in the magnetic fields around the world a similar device centered over Kansas would cause higher pulse levels, and likely more damage. The Russians did the most applicable testing, their magnetic situation being similar to the US. They popped a 300 kT device at 180 miles over Khezkazgan in Khazakstan (Test 184, or K-3). EMP damage within 600 miles was significant, with power distribution systems catching fire and radars being disabled. Radios were damaged, to varying degrees, out to about 400 miles.
A SREMP would be detonated at a much lower altitude, and effect a smaller area. But, the impact to individual devices would be much more devastating. A single SREMP has the potential to destroy essentially all solid state based and unshielded electronics for several hundred miles, but the damage fades quickly outside that high impact area.
Shielding does NOT have to be all that high tech. A closed and sealed metal ammo can, for example, probably provides enough shielding that a solid state device would not be affected within a pretty close range to the SREMP. Of course, you cannot use the device while it is in the can, the antenna lead would have to pierce the shielding.
People will talk about “hardening” electronics against EMP. People will talk about the fact that tube gear is naturally a bit “harder” in this aspect. The fact is probably that a close EMP will kill those portables you mention…but what is meant by close really is hard to define.
This whole subject is often debated. Science can support a lot of different viewpoints on it. There are a lot of places you can find printed material that claims a single device will kill all radios in the US...but they never seem to quote the science behind why they say that. And the people who really know are not going to talk about it
T!