A bit of thread resurrection here
I just resolved exactly this issue with my DAB radio. I had a Calearo antenna with poor reception and went through the mill with it trying to sort it out. I even spent 2 hours with my friendly Sextons branch trying to get it to work properly.
I never got to the bottom of it but only last weekend I fitted a Hirschmann antenna and the difference is profound. They're not even close. On a route where I would have 6 or more drop outs I now get none. Totally different beast. I used a one few years ago on a Subaru with a Philips head unit and that worked flawlessly too. Bought mine from Dab on Wheels.
No idea why but these Calearo antennas are no good our cars. Bizarre, but there it is.