How does electromagnetic spectrum allows wireless communications?
Let me make 2 suggestions. One is to consider how the propagation of different parts of the spectrum allows different kinds of communications: 1) Very Low Frequencies (VLF) from 50 kHz to a few hundred KHz allow very reliable long-range propagation. This is good for services such as time signals – I have a small clock, not much bigger than a wrist watch – that displays time from an atomic clock about 1500 miles away. It runs at about 60 kHz. (Many styles of such clocks are available.) Medium frequencies (up to tens of mHz) are useful for broadcasting, also for direct point-to- point communication over long distances (although nowadays it’s probably only amateur radio operators who communicate this way). Higher frequencies don’t propagate for long distances, so they are used for short-range broadcasts (such as TV), satellite communications, call phones, etc. Microwaves are useful for beamed signals. Also for very short ranges, such as wireless phones. Second aspect is the very fortunate
