In the early 80s where I lived, there was some kind of filler that, once removed, allowed you to watch HBO. It was housed in a green box exterior to each house,

In the early 80s where I lived, there was some kind of filler that, once removed, allowed you to watch HBO. It was housed in a green box exterior to each house, where the cable left the street and entered your house. I don’t know if it was a filter really. It was just an electronic component of some kind that screwed on/off. When you ordered HBO, someone visited your property to remove this thing.