In the 1920's a radio station in Schenectady, NY built a powerful
transmitter. In those days before FCC regulations, not knowing just
how big to make a transmitter in order for the signal to be received
some distance away, the station set up to broadcast at 500,000 watts.
It requires about one watt to be received four blocks away. A cell
phone is three watts. This station broadcast at such tremendous power
that they could be heard around the world. People in New York didn't
even need radios. They could sometimes hear voices in their furnaces
and coming off chain-link fences. Light bulbs lit up in people's
houses even if they were switched off. - from www.clip-text.com