I know that it’s electrowaves but how does it become sound again ? How are there several channels ?
In: Technology
I see several useful answers addressing various bits of your questions. I will take a shot at the “how does it become sound again” bit.
As others mentioned, sound is simply a vibration that our ears are perceiving – mostly in air, but sound can actually travel in liquids and solids. The last bit is not very relevant right now, but handy to know.
As a vibration, it can make other things vibrate, and vibrating things (thing something like a guitar string, or a metal strip stuck on one end) will make the air vibrate, creating sound.
One important technical bit here involves how magnets interact with electrical currents: if you move a magnet through looped wire, it will induce current in the wire, and vice-versa – a current in a wire looped around a magnet will make the magnet move.
This movement and the current will correspond to each other – so if a magnet inside such wire will vibrate (move back and forth very fast), so will the current, and current moving back and forth very fast will make the magnet vibrate.
If you attach such a magnet to something that is easily vibrated by sound in air, you can make the current that you get out match the vibration of the air.
You can do the opposite as well – send such a current that corresponds to a vibration of the air from elsewhere into a wire around a magnet that is attached to something that can make air vibrate around it, and you will receive sound that corresponds to that current. That is how speakers work – and the opposite is a microphone, of course.
So now you can convert sound to electrical “vibration” using the microphone, then send it somewhere else or even store it (on a tape, or something more advanced), and then play the sound elsewhere with the speaker.
The others have mostly explained the radio aspect of this – the vibrating signal is simply sent over the radio and received and played back elsewhere.
The actual sending and receiving works by sending a signal of a specific frequency, and the receiver then is made to only respond to that frequency – it is not 100% exact as nothing truly is, therefore it’s more like that the receiver will see the signal as the strongest when at that or near that frequency. This specific signal is called the “carrier wave”.
The vibrating signal is relatively low frequency compared to radio frequency, so it can be added up to the carrier wave and the receiver will still see mostly the same frequency it is set up for – and afterwards the actual information (the signal, the sound “vibration” we were sending) will be easily extracted by doing the same thing in reverse – it is a bit more complicated in case of FM than AM but it still works the same. Once the original signal is reconstructed, it is exactly the same as receiving it over the wire or playing it from a tape – send it to a speaker and you get the sound back.
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