svetz
Works in theory! Practice? That's something else
Saw a thread talking about Sol-Arc's ferrites for EMP protection and wanted to get some discussion on Ferrites for Lightning and/or EMPs. Haven't seen any EMPs hit around here, but we sure do get a lot of lightning. Ideally the goal of this thread is to get enough knowledge that someone would know enough to go to someplace like digikey and order what they needed.
I don't know much about it, but hopefully some of the EEs on the forum can clarify and answer questions. I can at least start with the basics I picked up in a few minutes of googling.
Ferrites work according to Faraday’s Law, that is the magnetic core around a conductor induces a back EMF in the presence of a high-frequency signal, essentially attenuating the ferrite frequency response.
CFL, Lightening, EMP
Ferrites are designed to work at specific frequency ranges, so what should you get? If you're trying to filter out office noises such as those from compact fluorescent lighting, you'd pick one designed for the EMI frequency range of the source (e.g., 2 kHz to 150 kHz for CFL).
EMP
For EMP, looks like there are different types:
Frequencies
Found this chart, so lightning looks like it's low up to around 10 MHz. EMPs seem to cross the entire spectrum depending on type.
Broadband Ferrites
I suspect the term "Broadband ferrites" is marketing upsell. But, they're advertised as have a wide range of suppression and might be the best you can do for EMPs. Could be, it's the same as any old type 61. Hopefully one of the EEs knows more.
Type 61
From this government document regarding EMPs:
That same document shows national maps where likely EMP strike points are and what the power might be based on range.
Huber+Suhner
From the same document, they reference an online tool for sizing. Ideally, you want any spike to be less than 150 kV/m, but I'm not sure how the calculator can be used to figure that out....
Greek to me. Hopefully, someone knows how to size appropriately.
Electromagnetic interference (EMI) is one of the biggest challenges faced during the production of any electronic device.
I don't know much about it, but hopefully some of the EEs on the forum can clarify and answer questions. I can at least start with the basics I picked up in a few minutes of googling.
How do Ferrites work? Ferrite beads (aka ferrite choke, ferrite clamp, ferrite collar, EMI filter bead, or even a ferrite ring filter) are passive electronic components that can suppress high-frequency signals on a power supply line. They are normally placed around a power/ground line pair that is incoming to a particular device, such as the power cord for your laptop. Many have room for the cable to be looped through for greater effectiveness. |
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Ferrites work according to Faraday’s Law, that is the magnetic core around a conductor induces a back EMF in the presence of a high-frequency signal, essentially attenuating the ferrite frequency response.
CFL, Lightening, EMP
Ferrites are designed to work at specific frequency ranges, so what should you get? If you're trying to filter out office noises such as those from compact fluorescent lighting, you'd pick one designed for the EMI frequency range of the source (e.g., 2 kHz to 150 kHz for CFL).
EMP
For EMP, looks like there are different types:
EMP’s frequency range, depends on the source. A nuclear weapon detonated at high-altitude produces relatively long duation EMP, thus contains low frequency components (100 MHz). Because conventional EMP devices produce explosions driven by HPMW technology, they may have a frequency in the range of 100 MHz – 100 GHz. EMP, depending on altitude and power, can generate electric field up to levels of 50 kV / m.
Frequencies
Found this chart, so lightning looks like it's low up to around 10 MHz. EMPs seem to cross the entire spectrum depending on type.
Broadband Ferrites
I suspect the term "Broadband ferrites" is marketing upsell. But, they're advertised as have a wide range of suppression and might be the best you can do for EMPs. Could be, it's the same as any old type 61. Hopefully one of the EEs knows more.
Type 61
From this government document regarding EMPs:
Ferrite beads are widely available online and cost just a few dollars each. Normally more than one bead is required to achieve significant attenuation (~10 dB). They can be clamped on, snapped on or slipped over cables near the equipment end to attenuate unwanted high-frequency cable signals. Type 61 (HF) ferrites made of Nickel Zinc are recommended. These are designed for inductive applications to attenuate interfering pulses from 200 MHz to 2 GHz. They can be added to existing cables or purchased with ferrites pre-built in common cable types. A wholesale distributor such as Digi-Key Electronics (http://www.digikey.com/en/products/filter/cable-ferrites/840) allows for filtering any combination of sizes and specifications to fit requirements...
That same document shows national maps where likely EMP strike points are and what the power might be based on range.
Huber+Suhner
From the same document, they reference an online tool for sizing. Ideally, you want any spike to be less than 150 kV/m, but I'm not sure how the calculator can be used to figure that out....
...insert the “RF CW Power in W” (Watts), the “DC Supply Voltage” (normally zero), the maximum antenna “VSWR” (normally at least 3), and the “Impedance Z” (normally 50), and then click on the “Calculate” button. Using the H+S online calculator for three typical powers of 100, 400, and 1000 watts (with a 3:1 VSWR) results in the following required GDT voltage ratings:
100 watts has a peak voltage of 150 volts
400 watts has a peak voltage of 300 volts
1,000 watts has a peak voltage of 474 volts
That is, the 350-volt GDT may strike at only 298 volts, the 600-volt GDT may strike at only 510 volts, and the 900-volt GDT may strike at only 765 volts. Going into more detail for the last example above, a 900-volt GDT is used despite a calculated striking voltage of 712 volts (to protect an amplifier with an output power of 1,000 watts) because it might strike at a voltage as low as 765 volts with its 15% tolerance. This means that the voltage induced in the antenna lead from a lightning strike or EMP will reach at least 765 volts before the GDT fires. But the induced voltage could go up into the thousands of volts without the surge protector. Also, a VSWR of 3 may only be nominal: Many VSWRs will be higher, requiring GDTs with even higher voltage ratings. Disregarding the safety factor and the tolerance would result in selecting a GDT with a striking voltage that is too low, compounding false triggering problems.
Greek to me. Hopefully, someone knows how to size appropriately.
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