I was thinking about time-cones. They're really 4 dimensional - a sphere that starts as a point and expands at the speed of light. That describes the motion of a radio wave. But time cones have a theoretical reverse side thats symmetrical to the normal forward direction. The sphere would have negative radius.
When a radio station transmits a signal, there could be energy from the reverse side of the time cone converging on the point of transmission until the time it is transmitted.
It should be possible to recieve a signal from the reverse side (backwards of course). Get 2 signals separated by some function of the signal's wavelength (somewhere around 2 meters), and add or subtract them together to do something to the phase, reverse them, then send that signal to the antenna of a radio. In other words, assemble the parts of the reverse side of the time cone before they converge in the future.
I'm not sure about the math of it. Can anybody help?