Fm Radio signal?

There was a black wire included (with a metal "cap" to insert in the FM center connector) that served as the FM antenna, but in a pinch any wire can do, preferably about 33" long and with the insulation stripped from the last inch or so (or get creative and sand the last inch of varnish off a properly sized untwisted clothes hanger and gently bend to suit). Bare stranded wire should be twisted or folded until it's thick enough to firmly fit the middle "hole" of the FM antenna connector. Be careful that no strands of wire short to the metal ground "ring" surrounding the hole or the antenna won't work (although it won't burn out your amp like shorting the speaker wires would, it just won't work). Orient the wire horizontally or vertically for best reception. This unit also doesn't pick up FM very well if you're in a steel-framed building or away from windows in the general direction of the local transmitters, so moving the unit closer to a window may help dramatically. In bad reception areas you can get an external FM "rabbit ears" type antenna but you'll need the "European" style of 300 ohm to 75 ohm transformer to plug it into the unit's FM connector (one that has a bigger central connector "plug" than the usual US units). Some cable systems also still support FM, if yours does, a VHF/UHF/FM signal splitter and either the above mentioned transformer attached to flat 300 ohm cable or a plain  "European" style connector attached to the end of the 75 ohm round black cable will do the trick. Some Radio Shacks have them. Good luck!