The answer on this question is incomplete. It is only correct when the old aerial has no filter. There are aerials with a filter that only works up to 108 MHz. In that case for DAB+ reception (174 – 240 MHz) the aerial has to be replaced. Choose a type with a preamplifier direct under the aerial for best reception. Many types have two signalcables. One for the old radio and another for the DAB+ adapter. A third cable is for 12 V supply to the preamplifier.

This was my experience as a radioamateur when I bought a new car and replaced the old fashion radio that was still built in from the manufacturer.