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
> Why is it that we have a dozen or so different electromagnetic wave types
What do you mean? There aren’t really different types of electromagnetic wave,, we just call them different things depending on the frequency. Radio waves are not fundamentally different from light waves, they’re just longer. As long as we have a way to produce electromagnetic waves of a given frequency, and a way to detect them at the other end, then we can use them for communication by modulating a signal onto them. The simplest way to do that is to just turn the signal on and off, like Morse code – but more sophisticated methods are usually used.
But there are some frequencies for which practical technologies don’t really exist. For example, there is also the so called “terahertz gap”, where we don’t really have practical technologies for generating radiation with frequencies of between 0.1-10THz (i.e, higher than microwaves but lower than infra-red light).
Also, at the [very low end of the spectrum](https://en.wikipedia.org/wiki/Extremely_low_frequency), the wavelengths get so long that you would need an enormous antenna to radiate significant power. While some nations have built enormous transmitter stations to communicate with their submarines (these waves are the only ones that can penetrate seawater), it’s not exactly practical. And at the very high end of the spectrum (X rays and gamma rays) the radiation is harmful, so we don’t use it for communication (not that it would be especially practical to do so either).
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