Why does an AM radio channel require any bandwidth at all? Why can’t it just transmit on a single, precise frequency?
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Imagine a guitar playing some notes. If you strum one string that’s a single frequency. If we strum three strings we get a chord, which is made up of three frequencies.
The note A, (when you hear an orchestra tuning up, it’s the note they play at the beginning) is 440 hertz, which means it’s a wave that goes up and down 440 times per second. If you took a slow-mo image of a guitar string playing an A, you’d see it go up and down 440 times per second.
In AM radio, we transmit the “A” by changing the strength of the “carrier wave” which is the number you tune on the radio, 440 times per second. So you tune into AM570, well, if it’s playing an A, that 570 carrier frequency is getting louder and softer 440 times a second, which your radio decodes into an A and plays it.
Back to our guitar chord. We have three frequencies, A 440 Hz, C# at 555 Hz, and E at 660 Hz (these are all just musical notes, doesn’t matter too much which notes we pick). We then need to vary the carrier signal by a combination of all those frequencies, which leads us to have to have increased bandwidth. The more frequencies we add (like by a lot of people talking, an entire orchestra) then you need more bandwidth.
Interestingly, Morse code is great because it doesn’t need a lot of bandwidth, just the single tone it’s transmitting at, which is why a lot of ham radio operators (like me) use it still, as it can easily cut through interference, and you need less power to transmit longer distances.
hope that helps! Radio is tons of fun!
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