SHTF Radio preparation and models?

[Borage257]

Apparently emi gasket works. You’d have to take a wire wheel to the lip and inside of the seal are then apply the emi gasket.

[Lscott]

1 hour ago, Borage257 said:

Apparently emi gasket works. You’d have to take a wire wheel to the lip and inside of the seal are then apply the emi gasket.

This is the kind of info that’s useful.

[Borage257]

You need to make sure you get good bonding and seal between the lid and the body. I’ve read you also want some sort of insulator to keep things from touching the metal sides. Foam, plastic (hdpe cutting boards?) etc

[Borage257]

I’m much more concerned with non-emp power outages. Our local region has enjoyed record highs and several storm related power outages this year. Having robust power backups on individual radios (ht/mobile/base) as well as local repeaters is paramount.

IMHO grid down scenarios are more likely to happen from neglect, accidents, and non-emp terroristic acts than nation state or wide area emp strikes. I hope I’m right.

“Grid down, power up” is an interesting and somewhat sobering discussion on the state of the grid

[jsneezy]

13 hours ago, marcspaz said:

 

 

The idea of paying for an ammo can blows my mind.  For decades I have been getting them for free as packaging when I buy ammo.  I have lost count of the ones I threw away because I have to many of them and no room to store them one the ammo has been fired.

I buy ammo cans every now and then, but I also don't buy ammo any more. I pick up brass people leave behind and reload it. I also never pay more than $20 per can, and I hardly ever go for anything smaller than the 50 cal cans. 

[DONE]

Well, if we are gonna get into 'real' Faraday Cages, then lets actually talk about their construction.

First off, they are layered.  There is an outer and inner layer and they are NOT connected together. 

Hole size in the shielding material is what sets the minimum / maximum frequency that is blocked.  In other words.  A fine mesh will block a higher frequency than chicken wire will with 1 inch holes in it.  Consider the holes with regard to frequency wavelength.  If the hole is larger than the wavelength of the frequency in question, it will pass right through like it wasn't even there.

A strong understanding of the signal level and the attenuation level of the Faraday Cage needs to be taken into account.  A cage is not a perfect attenuator.  It has very high attenuation levels, but a signal that is strong enough will get through at a much reduced level. 

 

Proper construction.

A 2X4 or 2X6 frame is sufficient spacing to get a very high attenuation level with modest materials.  Those being standard wood framing and aluminum screen. For an added sense of security, thin sheet metal can be used in place of the screen.  You have an inner layer and an outer layer.  of the conductive screen material.  And remember they can't in any way be connected or you will loose attenuation properties.  The other thing you need is a GOOD earth ground.  This is not the 1 or 2 ground rods that are grounding your electrical service entrance, you will need to do better and it's advisable that the grounds be kept short as possible.  So if you are planning on building a cage, do it on the first floor or in the basement near an outside wall so you can get the ground wires out the wall and to the ground field withthe shortest wire possible.   Longer wires equal bigger antenna's and you don't want that. 

To put a door on the cage, you will need to ensure that the entire perimeter of the door be connected to the screens, both inside and outside.  Couple ways of dealing with this is either finger stock, copper or other metallic door trim / weather stripping, or construction methods that taper the inner and outer screens in a way that when the door / cover is in place that a 100% seal exists in all locations around the door inside and out.  

Again, can't say this enough, the INNER shielding material is NOT connected to ANYTHING including the outer shielding material.

 

For those that are looking to play around and build something similar to the professional level cages, this should be a good starting point.  Sure you can locate copper screen and use that.  It will work the best but it's also very expensive.  Not worth the money to protect your Baofeng radios. 

 

If you are REALLY wanting to go for broke and build a large cage, and be able to occupy the space, there are methods of bringing power and RF into the cage, but special filters and methods are required and are put in place outside the cage and are bonded to the same ground as the outer layer of the cage.  Remember that you need both layers of screening on all sides, including the roof and floor.  There is no reason that you can't set the floor screen and then sheet over it with layers of plywood or other subflooring material as long as the screening isn't molested (floating floor material.And of course you can also drywall the walls and ceiling but it's advisable to use construction cement and not screws to fasten the drywall to the framing.  Screws can be used sparingly to assist in placing the drywall until the adhesive is dry but will need to be removed after that happens to ensure the best isolation.  If you bring electricity into the cage, do NOT bring a ground with it and you HAVE to use an isolation transformer with proper filtering right at the entry point on the OUTSIDE of the cage,  DO NOT use conductive conduit to route wiring through within the inner shield. 

Detailed construction instructions are available on the web for building a Faraday Cage.  Study those plans carefully and scale your project to your needs.

 

 

[WRXB215]

7 hours ago, WRKC935 said:

Not worth the money to protect your Baofeng radios.

On one hand I agree. On the other hand, if that Baofeng radio is your only means of communication, it just might be worth protecting. Good writeup @WRKC935 very thorough.

[Borage257]

8 hours ago, WRKC935 said:

First off, they are layered.  There is an outer and inner layer and they are NOT connected together. 

 

Is there a distance (maybe function of wavelength) the gap between the two conductive boxes?

Could this area be filled with foam insulation?

[Lscott]

1 hour ago, Borage257 said:

Is there a distance (maybe function of wavelength) the gap between the two conductive boxes?

Could this area be filled with foam insulation?

I don’t see why not. If nothing else it might increase the attenuation a bit from dialectic heating of the foam material at very high RF frequencies.

[WRXB215]

@Lscott I know Styrofoam is bad about static electricity. Would that be a problem?

[Lscott]

1 hour ago, WRXB215 said:

@Lscott I know Styrofoam is bad about static electricity. Would that be a problem?

I doubt it. The general recommendation is to ground yourself before handling sensitive electronics as a safety precaution. They make conductive wrist straps for that purpose with a coiled wire lead you run to the nearest earth ground point or conductive matt.

 

 

[DONE]

Little bit of expansion on the discussion of DIY cages.

I have worked with commercial Faraday cages in the past doing RF work.  Reasoning was you can't truly evaluate the performance of a radio receiver when it has multiple RF signals near it. 

The commercially sold cages we used were a sheet metal room (technically sheet aluminum and not metal) with an aluminum frame that the outer shield was screwed to. It was also glued with a conductive construction adhesive.  The door on the unit was staggered and 6 inches thick with the inner face reaching into connect to the inner shield and had finger stock that surrounded the inner part and a separate ring of finger stock on the outer ring.  There was enough room in the cage for a workbench and the required test equipment, a chair for the desk and a bit of space to move around.  It was probably 6 by 6 or 8 by 8, but no bigger.  Special electrical filters were connected to the power feed for the interior and while there was a 'window' it was inset into the door and has copper screening on the interior and the exterior hole was also screened.  So it's technically possible to have a window, it still needs to maintain the 100% shielding inside and out.  Air ducts were connected to the HVAC but there were special screens that needed weekly attention to keep them clean as the screen material was a very fine mesh and collected a TON of dust and crap.

 

Again, there is no really secret sauce for building a cage.  The info is on the web. 

 

 

[AdmiralCochrane]

The EMP from a lightning strike in my yard damaged some stuff at my house a few years ago.  I had all my antennae disconnected, but the EMP was received on the wires between my power supply and my HF radio - a conductive loop. The end of the loop was the incoming power filter board on my HF radio, everything on that board was fried, but to be clear: the power was picked up and entered the radio via the wires between the radio and the power supply.  Since repairing the radio, I now not only disconnect the antennae when I am not using the radio, I also disconnect the power supply. Anderson Power Pole plugs plugged into a Rig Runner power strip. 

Another piece of equipment that was damaged and caused a dead short on one circuit breaker circuit was an old florescent light ballast.  Before the strike the ballast was weak and I had the tubes out of the fixture, but the magnetic pulse was enough to short it dead. 

As in the Carrington Event, loops collect the pulse.  The longer the loop, the more energy can be collected.  Shorter loops just won't collect as much energy, it's one of the laws of physics. 

[DONE]

17 minutes ago, AdmiralCochrane said:

The EMP from a lightning strike in my yard damaged some stuff at my house a few years ago.  I had all my antennae disconnected, but the EMP was received on the wires between my power supply and my HF radio - a conductive loop. The end of the loop was the incoming power filter board on my HF radio, everything on that board was fried, but to be clear: the power was picked up and entered the radio via the wires between the radio and the power supply.  Since repairing the radio, I now not only disconnect the antennae when I am not using the radio, I also disconnect the power supply. Anderson Power Pole plugs plugged into a Rig Runner power strip. 

Another piece of equipment that was damaged and caused a dead short on one circuit breaker circuit was an old florescent light ballast.  Before the strike the ballast was weak and I had the tubes out of the fixture, but the magnetic pulse was enough to short it dead. 

As in the Carrington Event, loops collect the pulse.  The longer the loop, the more energy can be collected.  Shorter loops just won't collect as much energy, it's one of the laws of physics. 

Oh, I certainly agree that lightning can be VERY destructive and not directly hit the equipment that it damages. 

Part of the R56 installation manual is the grounding and bonding section.  Now the standard that this manual is detailed to the point of the minimum distance between a rack and the cable tray above it and the distance from the cable tray to the interior lights.  Nothing is missed that you would find inside of a communications site.

I have seen where voltages were induced on metallic but non-electrified objects like file cabinets.  And yes, they are required to be grounded as well for that reason.  One of my favorite lightning stories was a personal experience from back when I was working in the computer field and one of our contract customers was the Ohio department of corrections.  One of their facilities had a control room that sort of stuck out off the rest of the building in an atrium sort of area, AKA "The Yard".  Of course this structure had 1 inch bars over the windows and it was the most physically secure part of the whole campus.  The lightning hit the outside of the building and traveled down the outside of the structure via the bars on it and then arced to the ground, which was evident by looking at the outside of the building.    The current was so high in the bar's that it created enough of a magnetic field to put colored bar's in all the computer monitors.  I had to go home and get a degaussing coil I had from working on television sets (old school CRT stuff) and take it there to get the screens fixed up.  You could tell it was the bars on the windows because the color bars were spaced perfectly with the same spacing as the window bars.  

But even that HUGE magnetic field that was less than 2 feet from a half dozen computers did no damage to and of the computers in the room that were up and running at the time of the strike.  Which further's my personal stance on the protection of electronic gear in a box of some sort to protect it from an EMP.   And with that situation, the bars weren't acting as a faraday cage, they actually increased the "EMP" energy getting into the building via the huge magnetic pulse they created. 

[MozartMan]

Speaking of Faraday box, what do you guys think of this?

 

[Lscott]

5 hours ago, MozartMan said:

Speaking of Faraday box, what do you guys think of this?

 

I don’t think that’s a good way to make one.
 

You do need to use metal tape on all of the seams. Any break will allow leakage into the container. That also applies to the bottom too since that most likely is just crimped on with a small gap. Better than metal tape is use a small torch and solder along all the seams.

Another poster mentioned a nested cage for the inner one must be isolated from the outer one. In the video that’s not the case. Not only that but the top of the inner cage is missing.

I think if the outer bucket was prepared correctly that’s a good start. Then install an insulated liner. A second bucket prepared like the first is where you place your electronics. That bucket then fits into the first. 
 

Now you should have a good DIY double Faraday cage. 

[WRWH978]

Might be a good weekend project, I found an extra one laying around. 

[Lscott]

8 minutes ago, WRWH978 said:

Might be a good weekend project, I found an extra one laying around. 

I don’t agree with how he tests it at the end with a meter. It’s says nothing about the electrical connection.

But the idea looks sound. My concern is tipping the can over and having something rip through the foil. 

[AdmiralCochrane]

Simply the physics of the length of the wire and whether it is connected in a loop.  No other magic. 

[DONE]

On 9/8/2023 at 8:39 AM, WRXB215 said:

On one hand I agree. On the other hand, if that Baofeng radio is your only means of communication, it just might be worth protecting. Good writeup @WRKC935 very thorough.

If you can afford the 50 bucks a square foot for the fine copper mesh cloth for a faraday cage large enough to stand in, you need to buy better radios than Baofengs and use sheet metal or aluminum window screen which would work almost as well.

 

[DONE]

One of the things here that needs to be addressed is gaps and holes.

Remember folks that you are trying to keep out RF and not water.  If it happens to be water tight, so be it, but it's NOT needed.

As mentioned before, hole size in the mesh is directly related to the frequency that can pass.  For those of you that are familiar with the DUGA over the horizon radar system that is in the former USSR.  That antenna design had a reflector behind the active elements of the antenna.  If you go look at some pictures of the site you will notice behind the horizontal cage elements there are vertical wires that are running top to bottom of the structure.  Those are the reflector for the 13Mhz signal that was used for the system.  Being that it's 13Mhz the wire spacing needed to be less than 1/4 wavelength apart from each other to be effective.  But those wires in their spacing were completely effective for that design frequency. 

On the other end of the spectrum look at the large home satellite dishes that were a mesh.  Those operated at 4 to 8 Ghz and KU band was 12 to 18Ghz.  Now those mesh dishes were an effective reflector for both C and Ku bands and if the dish was physically large enough it would have worked at any frequency below the max useable frequency of 20Ghz typically.  This again had to do with the hole size in the mesh.  So small holes or perforations in the container (Faraday Cage) isn't going to have a drastic effect on the attenuation performance of the cage. 

Getting all crazy and trying to seal up the smallest pin holes with aluminum tape is pointless.  Yes, all the sides need to be electrically connected but small holes are NOT going to destroy the ability of the cage to attenuate an EMP or other rouge signal source. 

 

Something else to consider is rise and decay time of a pulse. Although the pulse is only going to have one polarity, it can still be treated as an AC source.  This is the reason that the inner and outer shields are required for a proper Faraday Cage and the EXTERIOR is the only part that gets grounded.  This creates a capacitor of sorts that is single ended with one end floating (the inner shield) and the other grounded. 

 

[marcspaz]

All of that is only good for a damped sinewave pulse.... maybe. If you know a head of time, every wavelength that will occur. Likelihood of that is zero.

 

Truth is, every frequency from DC to daylight comes from an EMP. It will be in the form of electrical, magnetic, electromagnetic, radiation, and photon energy. Even the smallest of pinholes leaves you are risk.

[Lscott]

8 hours ago, marcspaz said:

All of that is only good for a damped sinewave pulse.... maybe. If you know a head of time, every wavelength that will occur. Likelihood of that is zero.

For a one shot arbitrary pulse shape you can use the Fourier Transform to calculate the spectra. In a prior post I had a link for a paper that had the mathematical model for a nuke EMP for reference and testing purposes. The transform  can be used to calculate the spectra. From that the parameters for shielding can be formulated.

https://en.wikipedia.org/wiki/Fourier_transform

[marcspaz]

9 minutes ago, Lscott said:

For a one shot arbitrary pulse shape you can use the Fourier Transform to calculate the spectra. In a prior post I had a link for a paper that had the mathematical model for a nuke EMP for reference and testing purposes. The transform  can be used to calculate the spectra. From that the parameters for shielding can be formulated.

https://en.wikipedia.org/wiki/Fourier_transform

 

I'll have to take a look at it tomorrow, when my brain isn't fried.

[WRYT685]

On 9/5/2023 at 8:48 PM, WRKC935 said:

And that was my whole point.  Thing is that the South Korea and China saw no damage either.  And I was at a loss to find any information on damage done in the US from tests when they were conducted, which was the point of what I said. 

EMP is a real thing, and I am not trying to minimize the effects of it when it comes to things like the electrical grid. 

But to hear some people talk about an EMP is that anyone with ear rings in will be electrocuted by the voltage induced between them across your head.  We had cars with computers in the 90's.  No one seemed to be effected by the EMP from any of the testing in that era.  Sure those detonations were below ground.  But if the EMP is that powerful to effect every car in the midwest from a high altitude air burst then how is it that no one was effected at all during any of the testing.  Or were those effects just not documented?  I don't know. 

 

I think your forgetting one important factor:  they were all BELOW GROUND.  The EM burst was strongly attenuated and dissipated by, well, the ground.  That was by design...the NORK government doesn't go out of it's way to piss off it's sole sponsor, the PRC.  Our government  learned from Starfish, and applied those lessons to future testing.

 

Exoatmospheric detonations won't be so attenuated, at least for some distance.