Ive had a look cant find anything to answer my question.

Ive changed my head unit from standard to a jvc kw-av50 every since really poor signal most of the time.

My set p is as follows did both with original aerial and after-market aerial

.

the booster did not help.

How much did this unit cost ?

http://www.caraudiocentre.co.uk/product_m-jvc-kw-av50e_p-27442.htm

£240 atm i pain £280 ish and its well worth the money

How is it well worth the money if it don't work?

Unless some technical guru can come with a solution I would be going back to the supplier as the unit may be faulty.

Well I paid 300 quid for mine fits perfect with the car has sat nav tv DVD player everything and mine works everywhere perfectly

I would send this back too or get your money back

The factory aerial has an amplifier built in to the base, this is powered by the cable on the factory stereo. The new one won't do that. You need to find a way of providing power to the aerial amplifier. You're probably best speaking to the shop that sold you the stereo for advice on this.