I have some powerline networking adapters which can transfer at a peak rate of 200 Mbps (I get around 60 Mbps typical, but I am sharing the network with many other devices and many pieces of equipment are running on the line.) How do they do it? I always thought that it was during the zero crossing, but packing so many bits into such a space must be very difficult, nigh impossible. HowStuffWorks has an article on it, but it's only relevant to adapters which go at 14 Mbps.
Answer
If you want a simplistic answer. Here it is
You have the power source. It gives you 220 Volts at rather low frequency (as noted: 50-60 Hz). You connect a capacitor with a low value and an inductance of a low value to this line this way: low inductance doesn't allow 50-60 Hz to pass in - it shorts such currents to the ground (being placed after capacitor! not to short everything at all), on the other hand capacitor in it's place again doesn't allow low frequency in and passes through high frequency, which we send or receive. The other party does the same - we have a working transfer line.
But, ofcourse we connect different devices to our power socket. What happens in such a situation is simple too: mostly they are - ac/dc convertors, which use either transformer, or impulse scheme. This schematic doesn't allow high frequencies, eg they provide huge resistance to it. But we remember the capacitor in both our devices - it provides low resistance, so our-generated high frequency signal takes the easiest way: our receiver. Ofcource there will be noise and leakage, our coding system and filters will deal with it.
That's the picture in it's simplest form.
Hope this is what you were asking ;)
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