for the radio, thanks do some bring the signals in better.

The 1/4 wavelength (approximate size) one's seem to work the best. The longer the better and centre or rear of the roof mount is better than boot mount on a saloon for example.

The shark fins and electric window type antenna's are crap even with their signal boosters.

I've used a Sony XDR-F1HD in a car with a mag mount band 2 antenna mounted in the centre of the roof and the results were phenomenal compared to the decent JVC receiver it already had fitted, in comparison.