how do you do it is there a +12v connection to the base?

Which bit of the aerial is actually broken? How did it break? Is your car under warranty?

A bit more description in the post would help people answer your question

Steve

no signal comming through to the head unit just hiss and the odd faint station, no phyical problem with the whip.

car is a W plate so well out of waranty.

Only one coaxial connector ,there is a push together connector about 6 inches down the cable .The aerial/base is held on with one big nut and a metal cage with spikes to earth the aerial.its a dead easy thing to change ,biggest problem is getting headlining down at the back to get at the cable and nut .The volts for the amplifier are fed up the coax

:)The radio has +12v sent down the co-ax to power the aerial rf amp in the base, so you could see if there is +12v coming out of the aerial plug for starters,there could be a short in the cable stopping the voltage or signal getting through. You would have to pull back the roof lining back to the base of the aerial, which I think its held on with a nut to replace the roof mounted mast.Hope this helps - Stuart.