this is not specific to the 178, but MOST RPods have a small red push button located on the cover plate where the cable/antenna connection is located. This is the antenna booster switch and by pushing the button in, the light should come on and the antenna is now functional. Usually, one must then do a channel search on the tv to find which channels are available in that area.
Note that the booster is powered by the 12volt power system and if left on it can draw down the battery if you are not connected to shore power. Turn it off when not in use if not on shore power.
Use the "search" feature at the top of the page to see lots of discussion about the antenna and booster.
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Vann