Radio/cassette player for a transit van?

I have a transit connect van 53 plate but have a sterio in it from a 2006 Transit Van, the radio and cassette work fine aprt from the fact that i cannot get Real Radio that is on fm 105-106 the last station found is one on 103.9fm. All the other stations work fine radio just does not seem to work beyond 103.9fm anyone got any ideas?