I have a "rubber duck" version on the front wing and from time to time all seems well and then I go through a phase of either poor or virtually no reception - recently fitting a new radio (fancy with Bluetooth 'phone connection ability!) I lost all am/lw signals and only after several attempts at reinstallation of the aerial did I get reasonable signals (fm OK throughout.
I get the impression that it is something to do with earthing but would appreciate advice