Hi all: Why is it that we have a dozen or so different electromagnetic wave types and yet every one of them can be used for analog and digital communication?
Thanks!
In: Physics
They’re not really different types. They’re the same thing on a continuous spectrum differing by only the frequency of which the wave occurs. The “types” are arbitrary divisions based on human applications. Visible light for example being what we see. Infrared being what temperatures on earth cause things to glow with. Radio waves being useful for electrical circuits. Xray for seeing through things. Nothing separates these. We don’t see UV, some animals do. Most things omit infrared from being hot, but turn you’ll stove on and you’ll see red come off. Your microwave oven and radio waves off your wifi router are actually the excat same thing, just very different power scales.
We can communicate with any of them, because all we do (and are fundamentally required to) with communication is vary the frequency a little to send a signal. Doesn’t matter if 10 kHz radio waves or 500 THz light, we can change the frequency a little in a pattern and send information with that.
The dumbest way is just pulse on and off. Basically, it’s a telegraph sending Morse code. We did this with radio waves in the past. And this is more or less what we do with fibre optics, we do not use the THz bandwidth efficiently yet.
There are more complicated ways too, that are way more bandwidth efficient. Bandwidth is literally the width of the frequency band you use. Make noise in the 50 to 450 Hz range to send your signal? That’s 400 Hz bandwidth. Make noise on the 10,000 to 10,400 Hz range to send your singal? Also using 400 Hz bandwidth. Switching on and off is very inefficient, as it makes a whole host of noise all over the spectrum.
FM is better. AM is even better, needing only twice the raw single bandwidth. Despite modulating wave height / amplitude, AM does use different frequencies too. E.g, if you send a 20 kHz audio signal (as that’s the range humans can hear), you’ll need 40 kHz of bandwidth with AM. That could be 40 kHz used on 100 kHz carrier (so 80 to 120 kHz needed). Thats why radio stattions carrier frequency (the station number) are spaced the way they are. Or it could be on 10 MHz, so 9.98 MHz to 10.02 MHz. Or it could be on a THz, we’re it’s a rounding error, basically. So, higher frequency do offer a LOT more capacity. There’s better than AM for techniques. For digital signals, we use things like QAM (quadrature amplitude modulation), which can hit 100% bandwidth efficiency.
We’ll probably never go beyond visible, at least not in the air. Why? UV, xray, and gamma rays are dangerous to us. And harder to make, control, and receive.
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