This NDB is at the south-west corner of the airfield. When we passed this spot the first time we only saw something that looked like a cable of an electricity distribution network and we drove on. So we asked at the airfield hotel and they phoned the tower for us. And then we learned that what we had assumed to be power lines actually was the NDB we were looking for.
We came along the south of Wellingborough over the A45 and turned onto the west ring road A509. On the ring road left onto the A4500 towards Wilby and Ecton. Near Earls Barton turn right towards Mears Ashby and Sywell. At Mears Asby left to Sywell. In Sywell the road ends at a T-junction, turn left. The south-west corner of the airfield is behind the bushes along this road. You can take photos by walking into those bushes. But we walked back to the roundabout and climbed the wall around the airfield.