3 ms·

There are gigabit PoE injectors, you can find cheap ones on ebay :) IEEE 802.3at uses phantom power, all 4 pairs can transmit data.

• stephengillie 13y ago
  I'm guessing they would take the existing voltages on each line and merely amplify them or similar. So the differential signal would just be using much higher voltage differentials. HVDS[1]? I'd never thought of it this way, but I suppose networking devices could be built to subtract the excess voltages and noise into a power regulation circuit, which would power the device. In effect, a switch or router like this could be called "unpowered" as it's not using the traditional wallplug powerbrick. [1]https://en.wikipedia.org/wiki/HVDS https://en.wikipedia.org/wiki/HVDS
  • kbaker 13y ago
    Close... Ethernet is isolated through magnetic transformers on both sides, so any existing common mode noise or DC voltage is removed leaving only the AC data signal. PoE (the standard, 802.3af/at) works by injecting DC power after the transformer on one side, and removing the DC before the transformer on the other side and using it to power the device. There is also a signaling mechanism to make sure the end device is PoE-compliant. Passive PoE as seen in the article simply takes out the two pairs of Cat 5 that are not used for data transmission, and uses them for power. It works in a pinch, but more caution is required to ensure the voltage injected is compatible with the device, there is not too much voltage drop in the cable, and there is not too much current going into the cable. Also, since these pairs are used for gigabit data, this method cannot be used with 1000baseT.