Which beacon is located 2.5 miles south of Hemel Hempstead, Hertfordshire?
Bovingdon stack:  It extends above the village of Bovingdon and the town of Chesham, and requires the VOR navigational beacon BNN which is situated on the former RAF Bovingdon airfield. RAF Bovingdon: Royal Air Force Bovingdon or more simply RAF Bovingdon is a former Royal Air Force station located near the village of Bovingdon, 2.5 mi south of Hemel Hempstead, Hertfordshire and 2.5 mi southeast of Berkhamsted, Hertfordshire, England.
the VOR navigational beacon BNN