So so little as our power lines are traveling light years across space without being stopped by anything electromagnetic, like the heliosphere?
The transmission of a radio signel is a function of frequency vs length of the antenna. As the Frequency is very low with power lines at 50 and 60 cycles a second you need very long antennas. The power grid is the largest antenna system in the world. So we transmit a huge radio signal at power line frequencys. If you are looking for low frequencys with your radio telescope, the earth is 50 times brighter than the sun.
Nothing stops that signal. It is so strong that if you touch the end of a osilliscope lead the 60 hz signal your body has picked up will show up as rather large voltage.
We all have a 60Hz buzz...