TAXI MAG MOUNT AERIAL FREE DELIVERY | eBay
One of those placed on a piece of sheet steel around 44ins dia with the whip cut to approx 23ins...its even got the cable and plug,
The supplied whip is to short at 500mm...I'm sure if you ask them to cut it longer they will do it.
Nick.
This maybe better,
http://www.ebay.co.uk/itm/TAXI-MAG-M...item3f1475d5c8