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Power Over Ethernet Injector


This project came from necessity and was a deep dive into the world of power over ethernet. For those not familiar with the concept, unused leads in the 8-conductor cable are used for powering remote devices. The particular applcation here was for a Ubiquiti radio that is on my roof, but it also has application for any other ethernet device where remote power is required as well. In the 10- and 100-Base T standards (twisted pair), only pins 1,2, 3 and 6 are used for the transmit and receive pairs, pins 4,5, 7 and 8 are unused. The 1000-Base T standard is a little more complex, and is really not required if the system runs at a speeds below 100 Mb/s. There are several versions of the POE standard, both AC and DC, this implementation uses the DC standard, with the voltage being source on pins 4 and 5, and ground on 7 and 8. In the AC standard the same pins are used as well, this board can be used for both.

In the amateur world we most commonly use 12v power supplies, with backup from some type of lead acid battery. The radios that were targeted for this application required 24v, so an off the shelf boost converter was purchased (see DC power project), to supply the requisite voltage, an this injector was used to supply power to the radios. It consists of a PCB with 2 independently powered channels, and a panel for rack mounting it. Individual LED's are provided for each side. It has been tested on the Ubiquiti Air Router and NSM radios.

The front panel was made by Front Panel Express in Seattle, they provide free software to capture the panel design, and the order can be placed online. The panel was designed to hold two converters and two power supplies for 4 radios.