quote:

---

Originally posted by ullix

That looks like giving a lot of honors to your counter, attempting to protect it from a Carrington!

I am not claiming high-frequency experience, but I doubt that a real world system will ever be 100% effective. It will be a "little" bit less.

Then the cell phone might not be a good choice for testing, because it will crank up its power until it gets a signal again (or to its max).

Not sure what would be better: wireless mice, routers, bluetooth audio, Walkie-Talkie?

---

quote:

---

Originally posted by Damien68

the faraday cage is one thing for electrostatic fields, ie static fields with therefore a zero frequency.
an RF shield is something else and is very complex.
with an RF field (non-zero frequency) to make it simple: the RF field will induce eddy currents in the shielding, these currents will then emit new RF waves and the waves will manage to pass through openings or seals ...
of course, we can make RF shields but within certain limits and under certain conditions, but we will never block all the waves, shilding only attenuate it.
The theory to assimilate to understand RF shielding is very complex.

Faraday's cage is an experiment that only applies to static fields. a lot of people confuse it but it doesn't work that way.

---

quote:

---

Originally posted by the_mike

Hi Steven

I'm currently building a faraday cage out of an old ammo-box, mainly to protect my new(ish) backup-drives (after the old ones were emp'ed out by a lightning two years ago - it's hard getting good source-material here).

My plan is to build it diffently than the usual YT-tutorial you can find for converting ammo-boxes:
1. i'll replace the tinfoil to replace the rubber-seal with some aluminium-mesh (I'll use window-screen against bugs), which I also will give a "holding layer" with solder (i'll bend the metal-holder for the rubber in a way it will clamp the mesh, and then melt some soldering tin into it to give additional "hold"

2. I'll also insert a 2nd "cage" within the first layer of nonconductive insulation, giving me a cage within the cage. I'll use the same window-screen alu-mesh as i use for the sealing.

3. still looking for a replacement for the cardboards. Initialli, I wanted to take some foam-material which was used to protect ...something i orderd (forgot what)... - but I found out it holds static. Maybe I'll go small (pressed) wood, I still need to be able to shape it into needed dimensions)

Maybe I'm just on the paranoid side here, but the lightning emp'ed so many devices away which were not connected to the grid (and many others which weren't unplugged in time), that I want to be save on that side, too (I already retrofitted surge protection to both fuse-box and all the plugs (as close to the devices as possible, to limit longer cables that might work as antennae for the EMP)

Disclaimer: not wanting to protect against a nuc. EMP - if one of these happens, I got other worries ;-)

EDIT:
for testing if your cage works, I'd recommend a radio.
Simple AM/FM and DAB.
Just set it to a station (a powerfull as in "close to you"), increase volume, put it in your cage. If you only get noise, change the band/frequency, repeat the test aso...
(also - the cellphone in flightmode and wireless lan, both 2,4 and 5 ghz)

Yes I know, radio-waves and wlan aren't necessairly good ways to check if something's save, but IMHO you'll get the most frequency-range to test this way - all within a typical "household enviroment", sure pros have (and would use) ..."other means"... to test.

---

quote:

---

Originally posted by the_mike

Hi Steven
Yes I know, radio-waves and wlan aren't necessairly good ways to check if something's save, but IMHO you'll get the most frequency-range to test this way - all within a typical "household enviroment", sure pros have (and would use) ..."other means"... to test.

---

quote:

---

Originally posted by Damien68

quote:

---

Originally posted by the_mike

Hi Steven
Yes I know, radio-waves and wlan aren't necessairly good ways to check if something's save, but IMHO you'll get the most frequency-range to test this way - all within a typical "household enviroment", sure pros have (and would use) ..."other means"... to test.

---

a "pro" would use a spectrum analyzer with a tracking generator.
the spectrum analyzer analyzes the rf power received by an antenna at a given frequency which varies following a sweep according to a scan pan. the tracking generator emits an rf carrier on the same frequency which therefore follows the same sweep.
also this makes it possible to obtain the diagram of attenuation according to the frequency.
but your way of doing is good and will give a first idea.

you can also use a GQ EMF meter to measure the power of a rf field with and without shielding.

---

quote:

---

Originally posted by Damien68

it's not very useful except for measuring the ambient field if you want to buy a house or rent an apartment. or to make experimentations like looking for and finding radio relays. or see the rf power of CB, walky talky or other radio equipment...

---

quote:

---

Originally posted by Damien68

it's not very useful except for measuring the ambient field if you want to buy a house or rent an apartment. or to make experimentations like looking for and finding radio relays. or see the rf power of CB, walky talky or other radio equipment...

---

quote:

---

Originally posted by ullix

improve? You mean, provided is has any "performance" at all?

A Faraday cage is defined as a means to protect against lightning, i.e. high voltage gradient electric fields, which may result in lightning.

When you connect this cage to ground, you may be creating a lightning rod. Never tried it, but I think I would then prefer to NOT sit in that lightning rod.

Imagine you sit in the car, and lightning strikes all around you. You don't feel in danger, because the car acts as a Faraday cage. And so you happily call home on your cell phone and tell them about the dangerous lightning.

Wait a minute, that car is a Faraday-cage, yet you can talk on a cell phone? Don't you also expect the F-cage is holding back all cell-phone conversations?

And you are also receiving GPS signals, so you can drive home while wild lightning strikes?

But your car sits on rubber tires, so is reasonably will isolated to ground. Therefore, you now connect your car via a metal wire with ground. Will all cell phone and GPS fail?

There is a difference in the physics of Faraday and lightning, and UHF frequency radio waves and metal-wire shields or meshes.

---

quote:

---

Originally posted by ullix

I think the guy rather convincingly demonstrated that his "Faraday cage" has no effect whatsoever against his radio waves, and grounding does not change this. Quote: "within margin of error".

---

quote:

---

Originally posted by Damien68

he's a guy who has great stuff and likes to show it off. But these numbers seem consistent. even if he shouldn't call it a faraday cage, for the scientific class it's prohibitive, this means that he does not know what it is. for the web class it is true that it can be different.

With its chicken wire, what is certain is that wavelengths less than the circumference of a mesh will pass through like in butter. therefore frequencies above 2-3Ghz will pass without even being attenuated.

he just did tests at 100MHz.
his R&S®FSH handheld spectrum analyzer have an Internal tracking generator he could have done very very much better with one more antenna and a coaxial cable.

100Mhz = 3m wavelengh
3m is largely much larger than the largest dimension of its "cage" so at this frequency he avoids a lot of compromising effects.
his experience for me seems valid but at 100Mhz, after that it's less sure but can remain more or less valid, in fact we have no data.

today electronic devices are subject to CE FC or FCC regulations, these regulations impose a minimum immunity to conducted or radiated EMI which for me is sufficient.

---

quote:

---

Originally posted by Damien68

technically, in fact a rf shield is indeed a faraday cage, but a RF shield is really more of that.

It will be best to speak simply of RF shield and leave mr Faraday in peace

---