radio propagation

Radio propagation is the study of how a radio wave actually travels from transmitter to receiver through the messy real world — bouncing off buildings, bending around hills, soaking into walls, and being swallowed by rain. Unlike the clean straight line of free space, real propagation is more like sound in a canyon: you hear echoes, dead spots, and a voice that fades as you walk. Predicting it is what lets engineers plan where to put cell towers.

Several mechanisms shape the journey. Reflection bounces waves off the ground and buildings; diffraction lets them bend over a hilltop or around a corner into the 'shadow' behind it; scattering spreads them off rough surfaces and raindrops. When many echo copies arrive at once they interfere, causing multipath fading — the reason a stationary radio can crackle while a moving one cuts in and out. Different bands behave wildly differently: AM signals hug the curved Earth and bounce off the ionosphere to reach across oceans, while 60 GHz waves barely cross a room.