What is propagation theory in wireless communication?

Answer 1

You are referring to a phenomena much beloved of shortwave and AM radio listeners, called simply "prop". After dark at night, the atmospheric conditions - especially in the winter time - allow for "bounce" of radio waves off the higher levels of the atmosphere. The effect can't be predicted precisely as far as effect, but the constant in it is that those radio waves travel much

further than they would in the daytime. In AM radio: A 5,000 watt station will carry only about as far as the deep suburbs of a city in the daytime. At night, especially in the winter, it will sometimes carry 2,500 miles - I speak from experience, I've logged it. Short Wave is the same, only more so: I have identified and logged a 1,000 watt station from Paraguay on a winter night. I live in Michigan, USA. That is roughly the equivalent of seeing a candle burning ten miles offshore at sea. And it's all because of propagation.