Whenever the control vehicle (which houses the main radio transmitter) parked at the parking area on the right just past the Peat Cott sign, we would have radio communication probs. Also some of us (me included) have noticed compass needles swinging in this area and between Nun's Cross and Fox Tor. This despite being careful about metal objects interfering with the bearing.
Hope this helps,
Share navigation tips, discuss map-reading, compass use etc.