How do radio signals reach around the world?
Radio signals are a form of light waves, just at a different frequency. Like light, radio travels in straight lines. If you can see a place from your station, you will be able to get a signal there. That is one reason why many antennas are very high up; you can “see” more from there. Radio is different from light because it bends more easily and can to a certain extent penetrate solid objects, although it has a harder time with a mountain than a sandpile. This is the reason that you can often talk to places, which fairly close, that you cannot “see”. Since the earth is curved, it doesn’t seem reasonable that a radio wave that starts off from your house in a straight line could reach the other side of the world. The trick is to bounce the radio waves off a layer, thousands of metres above us, called the ionosphere. This is quite possible using certain frequencies, typically below 30 MHz. The signal bounces back down to earth, often thousands of miles away and may then bounce back to the
