The theory behind radio technology is actually disarmingly simple.
To better demonstrate this point, here is a little experiment that practically anyone can do; first, take a fresh 9-volt battery and a small coin. Then, tune an AM radio to static (i.e. where there are no pre-existing signals coming through). If you place the battery relatively close to the antenna and tap the coin against the battery terminals, you will hear this signal relayed over the radio (it will break the static, effectively broadcasting the signal). You couldn't use this method for much more than Morse code (and probably only over a distance of a couple of centimeters), but still, it is a pretty impressive little experiment, is it not?
Well, basically, it all has to do with these things called ‘sine waves’. A sine wave is a radio wave that has been encoded in a specific way (this prevents it from getting confused with any other radio wave). Each sine wave operates along a different frequency, so there is no interaction between signals. Without sine waves (or any similar technology), it would be next-to impossible for us to use cell phones, AM/FM radios, walkie-talkies, TV, GPS and much more, because all the signals would interact with one another, all at the same time.
A radio, of any kind, needs a receiver. In the case of our battery experiment, for example, there is both a transmitter and a receiver. The battery/coin setup is the transmitter and the AM radio is the receiver. Radio devices that can both send and receive signals are called ‘transceivers’.
Again, this setup is actually quite simple. The transmitter encodes information (such as a TV broadcast, or a person’s voice) into a sine wave and then transmits it, via the electrons in its antenna. The receiver then captures the signal in the intended antenna (it has electrons that are coded to the same frequency as the transmitter) and then decodes it, using the radio’s internal system, so that the original information is readily available to the user.
The science behind the decoding process is a little more complex, but it isn’t really too difficult to grasp. We’ve run quite a few answers on the ‘ins and outs’ of that stuff lately, so check those out if you wish to know more. Thanks for your question.