RV Stereo Antenna cable issue

Thank you all for the quick replies. There is a round piece of plastic covering something on the roof right above the stereo area, so I'll check it. The black cable is hooked up into the exterior antenna socket on the stereo. The plate (winegard) on the wall above the stereo has 3 gray cables & other wires hooked up to it but no black one. I don't understand why FM would be blocked. I found the manual of the stereo but it doesn't say anything about the FM problem.