If you were to apply an electrical signal into one end of a wire, the current would travel along the length of the wire until it reached the opposite end only to be reflected back to the beginning. If you were to apply a second pulse at the exact same time of the second reflection, the current would effectivly add together. However, if you injected your second signal when the first...
The reason radio waves have the ability to diffract around buildings but a light sources do not is due to the wavelength of the signal. An antenna wavelength is determined by the wavelength of the signal you are receiving as well as the physics of the actual antenna...
