What you need to know about EMP weapons • Hacker News Board

Re: What you need to know about EMP weapons

#181

Post by genewitch » Sat, Jun 07, 2025, 5:02 PM UTC

jcrawfordor wrote: post #121

jvanderbot wrote: post #116

Earlier quoted context omitted.

https://en.wikipedia.org/wiki/Starfish_Prime > Starfish Prime caused an electromagnetic pulse (EMP) that was far larger than expected, so much larger that it drove much of the instrumentation off scale, causing great difficulty in getting accurate measurements. The Starfish Prime electromagnetic pulse also made those effects known to the public by causing electrical damage in Hawaii, about 900 miles (1,450 km) away f…

It should be understood that the largest impact of the Starfish Prime test, knocking out streetlights, was the result of a very specific design detail of the street lights that is now quite antiquated (they were high-voltage, constant-current loops with carbon disc arc-over cutouts, and the EMP seems to have caused some combination of direct induced voltage and disregulation of the constant current power supply that…

LEDs use constant current drivers, though. And even if you disagree, LEDs need to be current limited, so something will break with a large pulse of current, the driver or the LEDs themselves.

Maybe sodium lights are immune, in isolation?

Re: What you need to know about EMP weapons

#182

Post by grogenaut » Sat, Jun 07, 2025, 5:13 PM UTC

jerf wrote: post #105

Workaccount2 wrote: post #41

Earlier quoted context omitted.

Let me tell you something from first hand field experience with faraday cages... They attenuate signals, they do not block them. The common verbiage is to say "faraday cages block EM radiation", so people naturally assume that it blocks EM radiation. But I learned the hard way while doing compliance testing that no, they do not block EM radiation, they just weaken it (and it's highly frequency dependent on top of tha…

"(and it's highly frequency dependent on top of that.)" Well, sure. Can people inside the cage see outside? (Or a hypothetical person for a small cage.) If so, then clearly, not all frequencies are being blocked. A lot of "Faraday cages" are explicitly designed for radio and deliberately let other frequencies, particularly the visual range, through. In fact we all have direct experience with that. Our microwaves use…

"""General rule of thumb is that the opening in a Faraday cage should be smaller than 1/10th of the wavelength that should be blocked. For example, in order to block EM fields with frequencies of 10 GHz and lower, the hole size of the Faraday cage should be smaller than 3 mm."""

wavelength of red in inches: 2.46063e-5 wavelength of 2.4ghz in inches: 4.25 wavelength of xrays in inches: 7.87402e-7 (upper end)

You could easily see through a 4.25 mesh, that's almost chain link

you could not see through a 2.4e-5 mesh, that's call fabric, unless you can see through clothes in which case I'm not going near you. xrays can see through that :)

Re: What you need to know about EMP weapons

#183

Post by grogenaut » Sat, Jun 07, 2025, 5:14 PM UTC

Wobbles42 wrote: post #157

Onavo wrote: post #79

Earlier quoted context omitted.

Well, I am not sure how you expect redneck prepper types to pick up on enough RF theory to manufacture homemade metamaterials.

We aren't all rednecks. Or maybe we kind of are but some of us have engineering degrees.

a lot of people think if you get your hands dirtied you're a redneck... I guess I'm a redneck.

Re: What you need to know about EMP weapons

#184

Post by genewitch » Sat, Jun 07, 2025, 5:23 PM UTC

lostlogin wrote: post #164

accoil wrote: post #161

Earlier quoted context omitted.

Why does the coastguard get involved?

I think that 3T scanners are effectively transmitting on one of their frequencies in my region. We image hydrogen which has a precessional frequency of 42*3MHz at 3T (though most ‘3T’ MR scanners seem to be more like 2.8-2.9T). So they must use something at around that frequency. All I know for sure is that we got asked to stop blasting that RF out. Sometimes it is convenient to open the scan door while imaging.

126-128MHz if i am reading what you said correctly is aviation (aircraft use 108-136MHz, AM) - but i am unsure of what that notation means and the AI explanation made my eyes glaze.

I'm unsure why the FCC wouldn't be the ones to complain; but i've never managed to annoy a government with my radio-work yet, so i am not sure who calls who to send someone to knock on the door.

either way https://www.ntia.gov/sites/default/files/publications/januar...

also i only glanced the the US band plans, if this setup isn't in the US, then you'd have to find the relevant band plan for your area (although the US band plan for HF will be fairly accurate, HF is hemispherical on a bad day and global on a good day)

Re: What you need to know about EMP weapons

#185

Post by giardini » Sat, Jun 07, 2025, 5:52 PM UTC

nancyminusone wrote: post #62

>You can also forget about the inverse square law to protect you No, you don't get to ignore physics because the source is not a point source >Very large area of EMP How large? >Induces currents in any conducting material So does a magnet falling off my fridge. What magnitude of currents, at what distance, in what sized conductor? >During E1 the frequencies are so high How high are they? There can be radio waves stro…

nancyminuson says: "...There can be radio waves strong enough to melt glass vacuum tubes..."

Well, if it will melt glass vacuum tubes then it will likely smoke my a* - and my brain along with it. (Just following the directive: "...bend over and kiss your a* goodbye!")

Re: What you need to know about EMP weapons

#186

Post by timewizard » Sat, Jun 07, 2025, 6:22 PM UTC

resters wrote: post #170

Animats wrote: post #163

Earlier quoted context omitted.

That's a good point. Anything that is designed to survive lightning strikes also has considerable EMP resistance.

Communications equipment is not designed to withstand lightning strikes. Lightning protection is meant to prevent the tower from melting or the building from burning down, not to protect a receiver!

I'm not at all sure why you'd think that. Here's an actual product that sits inline with the coaxial cable and is absolutely intended to protect the receiver.

https://www.dxengineering.com/parts/ntk-pti-bb50nff?seid=dxe...

Re: What you need to know about EMP weapons

#187

Post by paulnpace » Sat, Jun 07, 2025, 7:25 PM UTC

There are also old Mercedes turbo diesels with mechanical fuel injection. I'm pretty sure those would survive an EMP, although I'm assuming things like starter motor circuit works (is it even possible to push start a diesel?).

Re: What you need to know about EMP weapons

#188

Post by lostlogin » Sat, Jun 07, 2025, 7:30 PM UTC

genewitch wrote: post #184

lostlogin wrote: post #164

Earlier quoted context omitted.

I think that 3T scanners are effectively transmitting on one of their frequencies in my region. We image hydrogen which has a precessional frequency of 42*3MHz at 3T (though most ‘3T’ MR scanners seem to be more like 2.8-2.9T). So they must use something at around that frequency. All I know for sure is that we got asked to stop blasting that RF out. Sometimes it is convenient to open the scan door while imaging.

126-128MHz if i am reading what you said correctly is aviation (aircraft use 108-136MHz, AM) - but i am unsure of what that notation means and the AI explanation made my eyes glaze. I'm unsure why the FCC wouldn't be the ones to complain; but i've never managed to annoy a government with my radio-work yet, so i am not sure who calls who to send someone to knock on the door. either way https://www.ntia.gov/sites/defau…

> I'm unsure why the FCC wouldn't be the ones to complain

Are you mentioned - US only.

I’m in New Zealand.

Re: What you need to know about EMP weapons

#189

Post by euroderf » Sat, Jun 07, 2025, 7:53 PM UTC

spacebanana7 wrote: post #93

euroderf wrote: post #91

Earlier quoted context omitted.

Responding to conventional weapons with a nuke ? Unlikely.

The USA did it against Japan. Of course those were special circumstances, but all wars have their own set of special circumstances to some extent. There’s also the argument that using nuclear weapons make sense when a nuclear state has a weaker conventional force that its opponent. Russia still has a pretty strong conventional force, but for example North Korea is in this position against most likely adversaries.

> There’s also the argument that using nuclear weapons make sense when a nuclear state has a weaker conventional force that its opponent.

Facing the Warsaw Pact, the US never renounced first use of nuclear weapons.

Re: What you need to know about EMP weapons

#190

Post by southernplaces7 » Sat, Jun 07, 2025, 8:32 PM UTC

wat10000 wrote: post #147

southernplaces7 wrote: post #143

Earlier quoted context omitted.

I thought the book was both harrowing as hell, grim to the point of being close to a horror novel in some parts with its descriptions of what people went through, and also extremely moving. The scene where Streiber manages to visit the wreck of his Manhattan apartment was enough to bring tears. I'm curious, What were your quibbles with Manhattan and San Antonio? Edit, and yes, I've read that it was highly praised for…

Mild spoilers here, I suppose! It didn’t make sense that San Antonio would be targeted in the limited Soviet strike. It would be pretty far down the list, definitely not in the top 3. I believe Streiber has said as much, and that it was included because of the personal connection, and the reason given in the book (some military headquarters there?) was a weak excuse. I can’t quite explain it, but it doesn’t feel righ…

Hmm, good points, but for the first one at least, the way I saw it was that the intended Soviet nuclear strike was supposed to be total, meaning hundreds of warheads for hundreds of targets, maybe even thousands for thousands.

That only a few actually landed was because of problems with Soviet strike capacity and of those few that got through, which ones actually did was mostly a question of random bad luck, so I just assumed that by said bad luck, one of them happened to be for San Antonio, which in a full, thousand-warhead strike, would almost certainly be one of the many targets chosen.

To elaborate a bit on that last point btw, I once saw a predictive map of all likely Soviet nuclear strike targets for a full-blown nuclear war in a military strategy book from the 80s (at the height of both countries' arsenals) that I used to have. It had hundreds of US cities and military installations with little dots over them, often just because they had even modest military or industrial significance. Apparently, if you're going to launch everything and have a lot to launch, might as well be generous with your delivery....

That's how I saw it at least, and at least it seemed like a fairly plausible justification for including San Antonio even though really, he just wanted to.

As for Manhattan, I also had a hard time believing it would be abandoned so totally, but the claim was that the bomb detonated especially dirty if I remember right, and bombs like that really can leave a place too contaminated to live in for many decades. There are atolls in the pacific where this happened from "mismanaged" tests in the 50s.

Either way, glad you (obviously) loved the book as much as it deserves!