I worked for a short time pumping figures into a VAX that "nested"
cut shapes together to minimize material losses in a sheet steel
plasma cutter setup. We had 3 machines, but the last one never
worked. It was a mere 150' feet from the VAX based machine controller
apparatus.
I noticed that the 9 conductor, foil shielded cable they used to
connect to the machine 150' away was draped directly over and snaked
around heavy power conduits that fed some of the high power machinery
being used in the shop (welders, shears, brakes, etc.).
I told them the reason their machine did not work was the routing of
that cable, as the spec for that particular serial line could traverse
much farther than a mere 150'. The noise introduced by the power
conduits was enough to keep the ports from handshaking/establishing a
connection for data transmission.
They bought a new cable, and routed it a bit better, and the machine
now functions.
This is why cable TV hard line runs are kept a minimum specific
distance away from power lines, both on the poles, and the soft coax
in the local installations.
LF fields can pass through both the conduits and the shields. Sure,
they attenuate some of it, but why ask for noise by nesting them right
next to each other.
Anyway... this proves your point.
