Optical fiber transmits optical signals. Coaxial cable transmits electrical signals. If it is used to transmit video signals, it transmits current signals. When it is used to transmit digital signals, it transmits voltage signals, because the signal at this time is 1 or 0. Current signals cannot distinguish digital signals 1 from 0, but voltage signals can. Coaxial cable can't transmit electromagnetic waves. We know that electromagnetic wave is actually a kind of light wave, and copper wire is used to transmit light ... You know the result, the attenuation must be very strong, and the short distance should be ok, but the long distance is not practical. ?

In the voltage signal, there are low level and high level (as shown in the figure). When it is low level, we can call it "0" and when it is high level, we call it "1". ?

Current signals can represent analog signals, and voltage signals can do this, such as the liquid level of a water tower. If expressed by current, the full liquid level can be expressed as 20ma, the zero liquid level as 4mA, and the intermediate liquid level will change proportionally. Similarly, the voltage signal is expressed by 0~5VDc or-10~+ 10VDc, depending on the sensor model or action mechanism you choose. Generally speaking, these devices have customized signal modes at the factory. ?

10 has been engaged in communication and self-control for many years. If you don't understand anything, just ask me.