Re: What is this Item, See Picture (below) ?
It is a powered TV Antenna. We have the same unit at our masthead that has proven to be very effective despite the switch to digital transmissions (so long as one has a digital TV able to decode the signals). The sliding A/B switch is to choose a feed to the TV, either the antenna or another signal source (on our boat an input from a shore side Cable TV hook-up). If the cable was chopped off, I suspect that was the result of a frustrated prior owner that likely had a problem with the antenna cable rather than the antenna itself. We had a similar problem when we first took over our boat but we were able to lead a new antenna cable through the mast and have been very pleased with the result.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."