how do radio signals (4G, WiFi etc.) manage to retain their information after passing through trees, buildings and other obstacles? And how are they not mixed up, intertwined?
In: Technology
It depends on the wavelength.
What you have to understand is that the signals you’re talking about are made of electromagnetic waves. Imagine a series of regular waves, with peaks and troughs. These waves have certain properties, including amplitude (the difference in height between a peak and a trough), and wavelength (the distance between two peaks). Waves with a short wavelength carry lots of energy but can’t go very far. Waves with a long wavelength carry less energy but can go much further. And by varying the amplitude of an electromagnetic wave (but keeping the same wavelength), you can transmit information.
Now, when an electromagnetic wave runs into an obstacle, such as a wall, it may or may not be absorbed by the atoms and molecules in that wall. See, atoms and molecules love to get more energy, but they can only take in specific set amounts, like lego bricks. If the incoming wave has just the right amount of energy, just one lego brick, then it will be absorbed by the wall and won’t be able to pass through. But if it carries less energy than what the atoms & molecules need to absorb, like half a lego brick, then it won’t be absorbed by the wall (the atoms and molecules can’t use half a lego brick, so they leave it alone).
Radio signals, like the radio in your car, have quite long wavelengths. This means that they can travel over long distances (easily hundreds of meters) without being much affected by obstacles in the way, like trees, walls and such (not enough energy to absorb). However, because the distance between peaks is larger, they can also convey less information at a time (the amplitude can’t vary very fast). Voices are fine, but forget full hd video.
Signals with shorter wavelengths, such as Wifi (microwave range), can convey much more information, but are more easily stopped by obstacles such as walls, which is why you need a wifi router in your home and not 200m away.
Now, as to why the signals don’t mix.
Between two radio signals: When you set your car radio to a certain station, you’re actually telling it to decode information coming along on one specific wavelength, and ignoring what’s happening on all the other wavelengths. Broadcasters have agreements between them, to say, I’ll broadcast on this wavelength, you can use a slightly shorter one, and a third broadcaster will use a slightly longer wavelength. That way you can listen to one broadcaster on each wavelength. Sometimes, signals will mix, because broadcasters haven’t agreed with each other and are broadcasting on the same wavelength!
Between a radio signal and wifi: these are along completely different wavelengths, so far apart that there is no chance of them mixing.
(For the lurking physicists – I know I’m oversimplifying like hell – sorry – but I really don’t want to go into quantum physics & scattering on ELI5)
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