[mdlug] Curious - Phone Tapping Tech

[Aaron Kulkis]

Michael Mol wrote:
> On Thu, Jun 21, 2012 at 1:32 PM, Aaron Kulkis <akulkis00 at gmail.com> wrote:
>> Robert Adkins II wrote:
>>> I am curious to know if phone tapping technology has "caught up" with
>>> Holywood. In terms of being able to take a band and wrap it around a bundle
>>> of phone lines and call that a tapped line.
>>>
>>
>> No.  Kirchoff's Current Law makes this impossible.
>>
>> Every current travelling "outbound" on one wire of a twisted pair
>> has an equal and opposite "inbound" current on the other half of the pair,
>> making the net current going through the loop = Zero, and therefore, no
>> way to detect ANYTHING  within the cable bundle.
> 
> That assumes the two halves of the pair are coaxial, which they're not.
> 

The only assumption I'm making is that the signal is carried on 2 wires,
and that the detector ("tap") wraps around both wires.

This sort of thing is covered very thoroughly in a college level
2nd semester physics course (Electro-magnetics optionally with optics)