Thinking about computers primarily, I'm trying to get my head around how data is transmitted along various transmission media. In particular, I'm getting confused between the use of electromagnetic waves (EM) and voltage (V).

Firstly, am I right in thinking that data can be transmitted using either EM waves or V, the former being analogue and the latter being digital?

Secondly, do guided media such as coaxial cables carry EM waves?

Finally, are buses inside a computer electronic? (is this the right word to use here?). I assume that volts are passed along each wire rather than EM waves.

I hope it is ok to ask three questions in one but they are all related. Detailed explanations (without being too technical) would be much appreciated.


Firstly, data moving in an electrical circuit moves as current (defined here as the motion of electrons through a conducting medium). The force that "pushes" that current is measured in Volts. I know that's a bit technical, but it can be very important to know.

As for one transmission type (be that optical, rf, audio, electrical, etc.) being inherently 'analog' or 'digital,' that simply isn't the case. Any signal can be modulated with analog or digital data. Analog or digital is a property of the data, not the transmission medium.

Coaxial cables, IDE cables, HDMI/USB cables, pcb busses, etc. are all forms of electronic transmission circuits. Waveguides ars a special case of elecronic & EM transmission medium. Fiber optics are a light/EHF EM transmission medium. RF antennae, speakers (including ultrasonic transducers), and the like can use air (or sometimes even vaccuum) as transmission media for their signals.

  • \$\begingroup\$ You may also find this related question interesting: electronics.stackexchange.com/questions/214229/… \$\endgroup\$ Feb 6 '16 at 21:24
  • \$\begingroup\$ So reading in a text book of mine it says that bits can be sent along a wire by varying the voltage on the wire. So does the voltage change create an EM wave of some sort that can be measured and interpreted as a bit? \$\endgroup\$
    – tommyd456
    Feb 6 '16 at 21:38
  • \$\begingroup\$ The textbook should have been written more clearly....but the end result is that varying the voltage potential on a wire will generally cause a measurable flow of current through the wire. That generated current, when opposed by some amount of resistance elsewhere in the circuit, will present a voltage potential to the receiving device. For DC, or near-DC signals, this will seem nearly irrelevant, but in RF & AF circuits inductances & capacitances can make tremendous changes in both current and voltage appear along a signal path, & not knowing to expect them can be disasterous. \$\endgroup\$ Feb 6 '16 at 21:45
  • \$\begingroup\$ Sorry, ran out of room: RF=Radio Frequency; AF=Audio Frequency. Both are electrical signals along wires for the purposs of my laxt comment (the importance of their frequency being in AC frequency vs aire speed calculations). \$\endgroup\$ Feb 6 '16 at 21:48

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