Ethernet transmission is broadband not tuned like a radio but the same equations as presented in the article hold across most of the bandwidth (where the skin effect holds). Actually, I am not sure whether the article is referring to tuned or broadband communication but in a sense it is irrelevant because practically, a large proportion of the energy transmitted in a modern broadband system is in the skin effect domain. If this wasn't the case, the system would be highly inefficient in the use of available bandwidth.
I take back by correction. Thanks, and sorry. Manchester encoding really is a form of phase modulation (BPSK). It makes sense to think of it as a 10MHz baseband signal modulated by a 10MHz carrier, and therefore having a 20Mhz bandwidth.
Because 50 ohms is an universal standard for most radio frequency equipment, not just microwave. It (often) doesn't make sense to invent your own coax, connectors, transformers, and chips. At the end of the day, the selection had its rational back in the days, but it eventually became an agreed convention that everyone just follows.
The convenience of existing cables and connectors seems to be the motivation.
> The first Ethernet used 9.5-mm coaxial cable, also called ThickNet, or as we used to curse it as we tried to lay out the cables, Frozen Yellow Snake.
> To attach a device to this 10Base5 physical media, you had to drill a small hole in the cable itself to place a "vampire tap."
> So-called Thinnet (10Base2) uses cable TV-style cable, RG-58A/U. This made it much easier to lay out network cable.
The neat thing about vampire taps is that you don't need to disconnect the cable so it could be done on a running bus topology network without interruption. If you did it right...
