How does sound travel in a radio?

Answer 1

Sound can generally be developed by three primary methods. AM, FM and digital.

In AM (amplitude modulation) the frequency is modulated, or to put it in layman's terms, the frequency is changed to be either louder or softer by changing the amplitude of the frequency.

In FM, the frequency itself is changed, either slightly higher or lower. For stereo, the frequency is divided into the + and - and each half is changed with what is called a stereo generator, that actually does the division of the frequencies into their positive and negative portions and than applies the modulation.

In digital, there's several methods. Digital can be applied to both AM and FM, and if seen in a spectrum analyser, it looks as though there's "little bumps" in various portions of the sine wave. In quadrature modulation, there will be four bumps per sinusoidal cycle, which can either be four parts of a single digital signal, or four distinctly different signals on the carrier wave. This can be multiplied several times to carry many signals on the same frequency.

In all cases however, sound is placed on the carrier (the frequency of the transmitter) as an electromagnetic wave. And in each instance, the receiver is of the type to match the type of wave sent out and they type of modulation.

Then the receiver has in it what is called a `descrimination circuit` which purpose is to separate the modulation (sound) from the carrier and convert it to usable information for the amplifier to convert to sound.

Digital operates a bit differently, but the end result is the same.

I know this is a layman's answer to your question, but we could spend hours on radio theory and only begin to scratch the surface. I any case, I hope you find this answer helpful, and maybe someone would care to add additional information.