 In this episode we'll talk about spectrum. Hi, I'm Tossus with RF elements. If you enjoy our videos, like, comment, and consider subscribing to our channel. Let's start with an electromagnetic wave. The electric and magnetic intensities of a wave change over time as it propagates through space. This is the representation in the time domain. A wave is characterized by the amplitude and frequency. To get that frequency, we simply count the number of times a wave repeats in one second. This gives us its frequency in hertz. The amplitude can be directly read from a time plot. For an electromagnetic wave at a single frequency, this is simple enough, but if we have multiple signals stacked on top of each other, this quickly becomes impossible to interpret. For this reason, we use the frequency domain. The x-axis of a time plot changes from time in seconds to frequency in hertz, kilohertz, megahertz, or gigahertz, depending on the frequency range of interest. An electromagnetic wave is now visualized as a spike at its frequency, and the height represents its amplitude. If we add frequencies to the signal, it becomes much easier to see what's going on compared to the time domain. This representation of a signal is called its frequency spectrum. From this representation, it's clear that the electromagnetic spectrum is a limited resource, which turns it into a commodity. If anyone else is using part of the spectrum, it cannot be used by anyone else. Signals would mix and interfere with each other. Increasing the number of users in the same spectrum leads to a point where all available frequency slots are occupied and no additional users can be added. In practical life, governments tightly regulate what applications each part of the spectrum can be used for and how much power can be transmitted. Some frequency bands are licensed. Users of this band have to pay for the right to use them. On the other hand, some frequency bands are designated as unlicensed. No licenses are required and everybody can use them. In both cases, authorities put technical requirements in place that users have to comply with, typically handled during a manufacturer's equipment certification process. If you like this video, consider subscribing to our channel for more interesting episodes.