[AT] Waaay OT

[Henry Miller]

On Saturday 11 March 2006 21:24, Larry D. Goss wrote:
> I know just enough about this subject to be REALLY dangerous.  Have any
> of you heard anything about this?  Or is this simply someone's wishful
> thinking?
>
> SUPPOSEDLY, some "farmer" somewhere discovered that he didn't have cell
> phone reception when he was in his barn.  He then discovered that the
> lack of reception was associated with a bar of cold hardened copper he
> was using as a door stop (or some similar mundane use).  He has
> discovered a way of putting the cold hardened copper into paint so it
> can be applied to ordinary walls in office buildings, schools, churches,
> theaters, funeral parlors...  Think of the possibilities! -- to
> automatically keep cell phones from disturbing meetings or events held
> in certain locations simply by covering the walls with a special paint.
>
> Is there any truth to this?  I'm well aware that the ordinary way of
> hardening copper is to cold work it, so what's with the "cold hardened"
> emphasis in the story?  And what's the hardening of copper got to do
> with it blocking cell phone signals -- but not pagers?  And why copper
> instead of lead?  Or is the whole thing a shaggy dog story?
>

In physics we call this a Faraday cage.    If a room is made out of something 
conductive (copper is most common, depending on what you want to stop a 
window screen might work), radio waves will not go through.   I won't bore 
you will all the equations needed to see what something will stop.  (I just 
barely passed that class, and it was 10 years ago)

The cold hardened stuff is pure BS.   Doesn't matter if the copper is hard or 
soft, copper is a good conductor, so it works well for this.

The door stop part is also BS.    What is important is that you have solid 
metal surrounding the room.  A door stop will not stop radio waves.  It might 
reflect waves enough that the cell phone can no longer find the signal in all 
the noise, but only if the signal is week.   Now if the signal is weak, wood 
conducts enough that it can stop them, but wood is not enough of a conductor 
that it can stop powerful waves.

The story was a farmer, who typically will live in an area where the signal is 
weak.   It is no surprise that a cell phone wouldn't work in his barn (Even 
in the cities cell phones have problems in houses because the signal is never 
very powerful).

Someone else posted a link to conductive paint that will work.   Been on the 
market for years.   Most places don't care enough to use it, they just 
pretend to care enough to make those who do think they care.