Say you have a transmitting whip antenna. If you send a quick DC burst into it, you will get the electrons in the antenna accelerating in one direction like this: If that EM wave is then absorbed by a receiving whip antenna, the electrons will also move in one direction. The polarity of the EM wave is only one direction. Conversely, if we do things normally and send an AC signal into the transmitting antenna, then the electrons will move back and forth which will transmit an EM wave with an alternating polarity. So am I right in thinking that a standard over the air radio signal is coherent light with 2 different polarities, while something like a laser is coherent light, but only one polarity?