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?

Owen
--

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

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


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.

Thanks Roy,

Given that BPL band plans often have a link bandwidth of several MHz,
one wonders also about the effectiveness of a trap in compromising
depth of notch vs bandwidth. Perhaps the magic bullet is really a band
stop filter, I didn't look the patent up.

But no matter, it seems it serves more to organise the location of
standing waves rather than eliminate current past the trap.

Of course, we are all scratching our head about the technical elegance
or even feasibility of BPL (or lack of it, more to the point).

Owen
--

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

In article ,
Owen Duffy wrote:

"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?

Might well be. A classic method of blocking single-frequency
interference current from flowing down a feedline is to stick a
parallel-resonant trap next to it. The commonest variety I've seen
described is a wire loop with tuning capacitor. I have no reason to
believe that a core-based version would not work.

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?

Could easily do so.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Wes Stewart wrote:

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?

This sounds like the "resonance breaker" someone mentioned recently. It
resembles a gamma match. You put a wire parallel to the tower for a few
feet, then connect the top to the tower through a capacitor. The bottom
of the wire is connected to the (grounded) bottom of the tower. This
alters the effective height, and therefore the resonant frequency, of a
tower. It's a technique used in the broadcast industry to reduce
undesired coupling which distorts antenna patterns.

I don't think this method will do more or less than a trap. There's
nothing which will stop current or energy at some point, as long as
there's mutual coupling from the wire on one side to the wire on the other.

I recall an EMI control class I took long ago, where they told how a
brute force power line filter was installed to reduce radiation from
circuitry inside a device via the power line. Worked fine in the lab but
failed in production. The filter was physically placed where there was
room near the front of the unit, and they found that the production
folks had neatly bundled the filter input and output wires for some
distance, providing a good path around the filter. The same sort of
thing happens on a wire with a trap, although the coupling is of course
not as strong as between the bundled wires.

Roy Lewallen, W7EL