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The power distribution in a house can be an excellent antenna

I discovered this when I was 12 about 100 miles from NYC with an early transistor radio. You can try this simple experiment to satisfy yourself. Take an inexpensive pocket radio and tune it to a weak AM station. Plug an inexpensive 2 wire extension cord like the type you'd use for a lamp into a wall outlet and bring the wire close to the radio. See if the signal doesn't become audibly stronger. Be careful not to reorient the radio as this can affect signal strength. This probably will not work nearly as well with houses wired with shielded wiring such as BX or in commercial buildings or high rise apartment houses wired in steel conduit. It also may not work well with heavy duty 3 wire extension cords due to capacitance to ground between the hot and ground wire in the cord. It works best with houses wired with Romex. The RF is capacitatively coupled between the wire and the loopstick antenna in the radio.

The best and most effective way to surpress rf noise on a power distribution network is with a suitable rf filter deisgned specifically for that purpose. The lumped parameter filter is the cheapest and most predictable method. Trying to devise a distributed parameter filter by adjusting the geometry and materials of a power cords is not only less effective and more expensive, it can compromise the primary function of the power cord which is to provide a safe and effective means to connect power to your equipment. It is easy to forget that simple power cords were the product of many years of engineering by the wire industry decades ago.

Connections in a distribution network can act as a diode detector demodulating rf noise present. This happened more than once but was most apparant with a problem created by a contractor who extended smoke detectors in a commercial building. There was a lot of internally generated rf noise in this laboratory building for the wiring to pick up. I discovered that the contractor had used solid wire while the original installation was stranded. Where the two joined, the junction acted just like a detector diode in a radio. The result was induced rf noise caused false alarms on the fire alarm control panel. The solution was to shunt it with a small capacitor and the problem went away. This is similar to what you get in many very inexpensive filters such as in power strips.

Every now and again I see problems of rf noise directly induced in circuits causing malfunctions. The best solutions I've found is to deal with it at the source where possible, otherwise effective rf filtering is the next best solution. Designing an rf filter by haphazardly redesigning wire is by far the least effective way and is one I would never consider until every other possibility had been explored and found ineffective. I'd usually give it little chance of being really effective.

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