Make sure the JVC radio menu has got "power antenna" selected to supply 12v via coax to antenna.
DAB/FM splitter also requires 12v (unless feed from radio supplies it)
Try to get the antenna element vertical if using an internal antenna as DAB Signals transmitted with vertical polarisation.
I have a JVC FM/DAB fitted to my 2010 +4 with on screen antenna which works well enough (screen does have heating wires)