[ale] [was] Re: Give application write access to /dev/console?

[Jim Kinney]

On Mon, 2017-08-28 at 15:20 -0400, DJ-Pfulio wrote:
> On 08/28/2017 01:36 PM, Solomon Peachy wrote:
> > On Mon, Aug 28, 2017 at 01:24:26PM -0400, Jim Kinney wrote:
> > > Love the line about the blocking ability in the sales lit:
> > > 
> > > Please Note: EMP DEFENDER BAGS are not intended to completely
> > > block 
> > > cell phone transmissions. Microwave transmissions from cell
> > > phones and 
> > > Wi-Fi equipment are not valid testing methods to determine the 
> > > integrity of a Faraday Cage.
> > 
> > Those aren't farady cages; they're glorified anti-static bags that
> > do 
> > bugger-all for RF shielding unless they are (properly) grounded.
> 
> Then why does my GPS, Bluetooth, wifi and cell signal NOT work when
> the
> phone is inside?

slap enough conductive material between source and antenna and
attenuation happens until not enough signal reaches the device. The EM
shielding materials I've looked at specifically to absorb/reflect cell
phone and wi-fi (lots of devices in the labs at work and a need to keep
them off the real network but still test connection for signal
processing of things like fitbit, motion trackers for movement
analysis, etc) all have specific wavelengths they absorb in. 
But yeah. Unless the outer metal layer is grounded, dual layers just
act like a capacitor in an RC circuit. That effect can be exploited to
attenuate signal as well as it tends to shift wavelengths re-emitted.
> I don't have the "EMP Defender", but I do have a pouch and it does
> work.
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-- 
James P. Kinney III

Every time you stop a school, you will have to build a jail. What you
gain at one end you lose at the other. It's like feeding a dog on his
own tail. It won't fatten the dog.
- Speech 11/23/1900 Mark Twain

http://heretothereideas.blogspot.com/
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