ethernet cable from antenna!

i ve just have my directional wireless antenna installed today for internet; i was expecting them to connect the cable from antenna to my wifi card; but there is an ethernet cable coming down from a box placed on antenna poll; a pigtail is connecting to the box and a cat5 ethernet cable is coming out of it. anyone has an idea what is it? and why is it used ?

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That is normal. What you are seeing is probably power over ethernet. What is likely there is a router built into the antenna enclosure. The antenna is connected directly to the radio card on the router. This is the best setup to keep the antenna cable as short as possible. Power runs up to the router through an unused pair in the cat5 cable.
Brian Rodgers