EMP-shield for small devices
- Thread starter rolnor
- Start date
Help Support Homesteading & Country Living Forum:
believe it or not - probably enough "leakage" around those handle and feet screw/ bolt holes to screw its Faraday usefulness
I think it comes down to the skin depth (something radio enthusiasts are quite familiar with) of the metal the enclosure is made of and what frequencies will hit it. Depending on the source of the EMP, there will be different frequency components invloved. With your smoker situation there, I would say the devices you currently have in it are small enough that none of them will act as efficient antennas below 100MHz. The question then becomes whether or not you have enough metal (thicker than the RF skin depth) at the frequencies of concern (>100MHz) so to prevent RF penetration. As for the screw holes, I wouldn't personally worry about that. Again, speaking as a radio enthusiast, radio reflectors are often made of things with holes. The important part is whether or not the holes are smaller than 1/100 or so of a wavelength at the highest strong frequency component anticipated and how much the insulated joints overlap each other (like painted surfaces bolted together acting as capacitors like the grill handle to painted metal). A spectrum analyzer would tell you that your microwave oven door, with all its holes, leaks RF (like crazy lol), but that mesh is reflecting most of the signal to keep it in the oven. Those holes/gaps will be of little consequence as those gaps are micrometer sized and what does sneak through will be heavily attenuated. Most of what leaks out of a microwave oven doesn't come from the holes in the window screen, it follows the metal surface and escapes around the door openings by the plastic parts as the insulated (painted) metal to metal closeness makes a poor capacitor at these places. Without a capacitive seal around the door, the cavity surface can act as a transmission line and RF can leave around the door opening. I'm rambling....
The frequencies of radiation that EMP's and nukes produce has already been discussed here so I will not repeat any of that.
Great, thanx!
I dont know the thikness of the tin in the smoker, maybe 0.5millimeter. I will probably buy a EMP-bag also and put my stuff in that first, then fit the bag, with some plastic insulation around it, inside the smoker. I think this is a very good protection. I have e-mail contact with the deffence agency so I will get their oppinion on this.
I dont know the thikness of the tin in the smoker, maybe 0.5millimeter. I will probably buy a EMP-bag also and put my stuff in that first, then fit the bag, with some plastic insulation around it, inside the smoker. I think this is a very good protection. I have e-mail contact with the deffence agency so I will get their oppinion on this.
posted it that it was a UTube - guy conducting the lab testing is a verified scientist - no problem with the facts >>> just with people who pretend to be looking for advice but dispute everything posted ....
A few feet of water will stop everything from HF to gamma rays and nothing under HF is a threat to your devices on account of wavelength. Just put it all in a sealed container and sink it to the bottom of the lake. Just don't use steel, magnet fishers will steal your cache.
Neutron radiation has no effect on electronics. Those particles are neutral so they do not interact with matter when flying through it. And yes, gamma is stopped by water. Ask anyone with uranium rods 
Water has a halving thickness of 7.2 inches for gamma radiation.
...not that any of this has any bearing on EMP protection, I merely wrote that to illustrate the range of stuff water can stop, in particular, RF.
Water has a halving thickness of 7.2 inches for gamma radiation....not that any of this has any bearing on EMP protection, I merely wrote that to illustrate the range of stuff water can stop, in particular, RF.
Last edited:
Yes, its true. But the fact is that neutron-radiation is very efficiently stopped by water compared to gamma. I read your post sloppy, sorry. But does water stop all types of HF? Is it not depending on the frequency? Microwaves in a microwave oven is offcourse stopped. I dont want to sink my power-generator in a lake, its brand-new… The idea to use a lake is low-budget, clever.
Submarines need to use VLF signals to get through the water (as skin depth thus penetration is a function of wavelength). The only frequencies that can penetrate any significant quantity of water are of such long wavelength that the devices you are storing are too small for the wires inside to act as antennas.
I doubt your generator will be affected unless it is full of solid state components (most are not).
I doubt your generator will be affected unless it is full of solid state components (most are not).
Its a electronic inverter I am afraid, its full of semi-conductors. A powerfull HEMP though, does only attack the devices connected to the electric grid. At least a few miles from ground zero. At least thats what I read so far.
That is not particularly true (about it having to be powered). I'll explain.
Older transistorized devices will probably be fine, its the newer CMOS and MOSFET stuff that gets cooked. The current induced on the devices wires from the EMP will put a voltage on the gate of these tiny switching devices. When the voltage is high enough to punch through the oxide layer under the gate, it ruins the switch (this is why it does not necessarily need to be powered, some mosfets can be blown with 12v, thats how thin the insulation is), or, if it is merely enough to turn the switching devices on for a moment, its game over either way.
In the case where the device is powered but are not immediately damaged from overvoltage, you have hundreds of thousands of solid-state switches turning on at the same time which causes the integrated resistors and current sources to overheat and burn out.
Older circuits made of discrete BJT transistors can handle a little HV abuse because the avalanche event will be limited by the circuit's resistance (and there is no gate insulation to destroy). These can still get blown up, but they are far more resilient because they can dissipate heat better and had over-rated components. Back when they made things to last anyhow.
One of my pieces of test equipment for radio work (a homemade pulse generator for doing time-domain reflectometry on coax cables) intentionally uses high voltage on a low voltage transistor. If you exceed the reverse breakdown voltage while limiting the current to something that will not damage the device, it resets after it avalanches and becomes an oscillator with an incredibly fast rise time and pulse width. I think mine goes from 0v to 10v output in about 0.6 nanoseconds when the supply capacitor charges to 120v. When it fires, the pF capacitor drains, the voltage drops, and the cap starts charging again (cycle repeats at about 50kHz). It is fun to send a pulse down a cable then watch the reflection on the scope return moments later, and the shape of that returning pulse and when it arrives speaks volumes about the cable characteristics.
Older transistorized devices will probably be fine, its the newer CMOS and MOSFET stuff that gets cooked. The current induced on the devices wires from the EMP will put a voltage on the gate of these tiny switching devices. When the voltage is high enough to punch through the oxide layer under the gate, it ruins the switch (this is why it does not necessarily need to be powered, some mosfets can be blown with 12v, thats how thin the insulation is), or, if it is merely enough to turn the switching devices on for a moment, its game over either way.
In the case where the device is powered but are not immediately damaged from overvoltage, you have hundreds of thousands of solid-state switches turning on at the same time which causes the integrated resistors and current sources to overheat and burn out.
Older circuits made of discrete BJT transistors can handle a little HV abuse because the avalanche event will be limited by the circuit's resistance (and there is no gate insulation to destroy). These can still get blown up, but they are far more resilient because they can dissipate heat better and had over-rated components. Back when they made things to last anyhow.
One of my pieces of test equipment for radio work (a homemade pulse generator for doing time-domain reflectometry on coax cables) intentionally uses high voltage on a low voltage transistor. If you exceed the reverse breakdown voltage while limiting the current to something that will not damage the device, it resets after it avalanches and becomes an oscillator with an incredibly fast rise time and pulse width. I think mine goes from 0v to 10v output in about 0.6 nanoseconds when the supply capacitor charges to 120v. When it fires, the pF capacitor drains, the voltage drops, and the cap starts charging again (cycle repeats at about 50kHz). It is fun to send a pulse down a cable then watch the reflection on the scope return moments later, and the shape of that returning pulse and when it arrives speaks volumes about the cable characteristics.
I know new semiconductirs are more sensitive. But in some sources they claim that the entire US will be affected by a HEMP, also even as far as Kanada or Mexico and this is the grid, not a handheld mobilephone..I have seen sources support this but I have contacted the military here in my country, I want this confirmed. Thanx for you input, its valuable to me.
- Joined
- Sep 7, 2013
- Messages
- 18,680
The references I've seen about Nuclear EMPs not affecting disconnected devices were talking about atmospheric Nuclear EMP tests (NEMP), such as the 1958 Teak Test, which was detonated at an altitude of 77 km. That was an atmospheric detonation, not a true HEMP. (The atmosphere goes out to 85 km). With an atmospheric detonation, the E1 component is mostly generated by the device itself, and at an altitude of 77 km, it's too far away from the surface to have any significant E1 component at ground zero.
A HEMP device is detonated at something like 400 km (250 miles) out in space. There are no "ground zero" effects because it's too far from the surface. So anything you read about nuclear EMPs that talk about "ground zero" are not talking about HEMP devices. Or they are confused about the difference between HEMP and atmospheric NEMP devices.
The E1 component of a HEMP is generated by interaction of Compton electrons (produced by gamma rays hitting air molecules) and the Earth's magnetic field. Under the right conditions it can cover most of the Continental US.
Wavelengths of the E1 component are in the range of 1 micron to .3 mm. There are plenty of circuits in every integrated circuit that can act as antennae for wavelengths in that range.
What I by ground zero is something very close to the detonation device, right under it. But I get your point, I know that HEMP:s covers a large area. But. i still want to check this, I find it difficult to beleive that enough milliamps are generated in a small mobilephone over this large area. And I have seen sources that imply that the danger only applies to stuff plugged in to the grid. And this I understand, the grid is a very large antenna and can transfer current over large distances. I will check this and come back.
- Joined
- Sep 7, 2013
- Messages
- 18,680
Check your sources, and then check their sources. Not saying I don't believe you, actually I do because I think I have seen the same sources, but when I check where they got their info from, it wasn't from a true HEMP test it was from an atmospheric test.
Two things regarding the E1 component...
1) The 1958 test was before CMOS technology was commercialized (by RCA in the 60's), so the result of that test is absolutely useless today (short of telling us what is produced electromagnetically).
2) All one needs to do to protect their equipment from the E1 component is to install TVS diodes after the fuse (to ground) and before the rest of the circuit. They go from an open circuit to a dead short extremely fast in response to surges. Once it triggers, it continues to shunt the surge until the fuse (fast burn in this case) blows disconnecting the device from power. Cheap insurance and no need for a faraday cage.
What has been on my mind lately is whether or not the box of TVR 14241 MOV's I have would also work. One of those saved my neighbors battery charger from a lightning strike (hence my purchasing 100 of them) ~ I needed one to fix the charger and all I could find is a bulk box. Now I have 99 left lol.
I will do that and I am open to to the fact that I could be wrong about the effects of HEMP-bombs
Do you think CMOS are present in my powergenerator/inverter? Are these in all electronics today?
Yes, there certainly are MOSFETS in inverters (CMOS are merely complimentary MOSFETS in a push pull configuration). What kind of generator do you have? I cannot see why a generator would have an inverter as they are already AC devices. Are you using a gas generator or batteries/inverter?
Yes, they are in almost all commercial electronics nowadays as they require very little current to operate compared to bipolar transistors.
Interesting side note. Once upon a time, EMP-proof magnetic "amplifiers" saw limit use, especially in rockets or places where vacuum tubes might be destroyed. There was even an audio amplifier built using this technology. It is essentially an iron or ferrite core inductor carrying AC current with a larger control winding. When DC is applied to a transformer, the core saturates (which is the same to the AC signal as removing the core). Removing the core (or saturating it) causes the inductive reactance of the AC winding to drop which allows more current to pass through it. To use that as an amplifier, the ac control signal is of a magnitude such that the control signal controls the saturation of the core (hence the necessity of a sharp B-H curve).
Yes, they are in almost all commercial electronics nowadays as they require very little current to operate compared to bipolar transistors.
Interesting side note. Once upon a time, EMP-proof magnetic "amplifiers" saw limit use, especially in rockets or places where vacuum tubes might be destroyed. There was even an audio amplifier built using this technology. It is essentially an iron or ferrite core inductor carrying AC current with a larger control winding. When DC is applied to a transformer, the core saturates (which is the same to the AC signal as removing the core). Removing the core (or saturating it) causes the inductive reactance of the AC winding to drop which allows more current to pass through it. To use that as an amplifier, the ac control signal is of a magnitude such that the control signal controls the saturation of the core (hence the necessity of a sharp B-H curve).
Last edited:
Thanx.
Very interesting amplifier, was it any good? Can you use it for HiFi?
I have this box with all my stuff, including the smaller smoker so its 2-layer nested.
Its a petrol-genenerator and it says its a inverter. There is led-display that shows Watts and Amps so clearly it containes semi-conductors.
- Joined
- Sep 7, 2013
- Messages
- 18,680
Yes, it's a thing.
The idea is to use the generator to charge onboard batteries which then power an inverter instead of delivering A/C power directly. The generator engine doesn't have to run at a constant RPM since the battery charger input voltage and frequency can fluctuate without causing any problem. It is supposedly more efficient since the engine doesn't have to run flat out all the time.
Downside is that because they contains batteries and an inverter, they have smaller output for the same size and weight as straight generators, and are more expensive for a given rating.
I essentially do the same thing, but not all in one unit. I use a generator to recharge an AGM battery bank for a 6/12 KW inverter. The generator doesn't have to run all the time for me to have constant A/C power.
But in my case, while the batteries are charging, I use the A/C from the generator instead of from the inverter.
Thanx DrHenley, very helpfull. I have a switch I can flip going from full speed all the time or use the possibility to run lower rpm if the load is lower, now I understand how this works. I also think sensitive electronics are running better with a inverter because you get very steady current.
Would it be possible to test a EMP-box with the HF from a microwave oven? You could bypass the door-breaker on the oven and place the it close to the EMP-box and run for one minute. One could have a HF-meter inside the box and se how much gets through.
No, because microwave ovens run at around 2.4GHz only and many things block that frequency. If you want to test the effectiveness at specific frequencies, it is better to put a receiver in the box and see if it can still receive. Although it is a safer method than setting the RF in your microwave oven free, the broadbanded nature of these EMP events makes this type of test kinda pointless.
You could always build an explosively pumped flux compression device and test it yourself... Wikipedia has some really nice drawings on how they work
Obviously I am not suggesting building a big one, but perhaps something the size of a beer can. You should be able to get a couple terawatts out of a device that size. They are disturbingly simple devices to build Terawatts??? Are you serious? I will check that out…No, because microwave ovens run at around 2.4GHz only and many things block that frequency. If you want to test the effectiveness at specific frequencies, it is better to put a receiver in the box and see if it can still receive. Although it is a safer method than setting the RF in your microwave oven free, the broadbanded nature of these EMP events makes this type of test kinda pointless.
You could always build an explosively pumped flux compression device and test it yourself... Wikipedia has some really nice drawings on how they work
Well, without knowing exactly what you are doing and getting the timing of it all just right, maybe less, but a little practice and some pissed off neighbors and you should be able to get it dialed in lol
I am borderline joking that you should build one, but it is a realistic possibility for one to be able to do so.
I am borderline joking that you should build one, but it is a realistic possibility for one to be able to do so.
Last edited:
Found this, I guess uts to small:
https://www.ebay.com/itm/185345240027
https://www.ebay.com/itm/185345240027
