On Mon, 13 Mar 2006 23:04:03 -0800, Roy Lewallen
wrote:

Owen Duffy wrote:
You probably haven't thought of powerlines as an antenna, the BPL
industry pretends they aren't, but they are.

A recent news item is about a new patent for a "Filter for segmenting
powerlines for communications" (US 7,005,943). It is described:

"There is provided a method for blocking a portion of energy of a
signal in a power line. The method includes equipping a high frequency
magnetic core with a coil, connecting a capacitor across terminals of
the coil to create a resonant circuit that resonates at a frequency of
the signal, and placing the magnetic core around the power line, at a
location where the blocking is desired."

Hmmm, a trap! Without getting bogged down in the details of the coil
and the current / phase relationships, is this likely to be effective?
A parallel resonant trap in an antenna doesn't eliminate current
beyond the trap at the frequency of trap resonance. Will it make the
region of the powerline between the injector and the trap a better
radiatior for the same injector power?

Thoughts?


You're correct that a trap doesn't stop current -- or energy -- at the
trap. The lines on both sides couple with each other, allowing
substantial current to flow on the side away from the source. All the
trap does is guarantee a current null at some point. A quarter wave
away, a current maximum will occur. In fact, a trap can increase current
coupled into a wire if it breaks a formerly non-resonant wire into
pieces of which one or more are near resonance.

Roy Lewallen, W7EL

Hmmm. Interesting. I'm too busy to think much about this at the
moment but Devoldere has something in his book (p. 9-27 in my old
Third Edition) about decoupling a tower from ground using a "linear"
parallel-tuned trap.

Does this not work?

Wes