Outdoor enthusiasts are being warned of a series of military jamming exercises that may put their GPS receivers temporarily out of action in the coming months.
The first will take place, as we reported earlier, around the Stanford Training Area, north of Thetford in Norfolk, at the end of this month.
Ofcom said land within 5km (2¾ miles) of the military range could be affected.
The Peddars Way and Norfolk Coast Path both run close to the Stanford base.
The exercises will take place between 8am and 5pm from 26 March to 30 March inclusive.
Walkers, cyclists and other outdoors users of GPS will have to make sure they have conventional means of navigating, using a map and compass.
GPS units will also be affected by two jamming exercises on the Cumbria-Northumberland boundary.
The first will operate around the Spadeadam base on weekdays between 9 and 20 April inclusive, from 7am to 8pm, and a second jamming session will be held at the same site, which is home to the UK’s Electronic Warfare Tactics Range, from 21 May to 1 June inclusive, from 7am until 8pm.
The jamming is likely to affect any GPS units up to 5km from Berry Hill in the Spadeadam Forest.
The Hadrian’s Wall national trail lies 2km further south and there are few public rights of way in the jamming area, though there are tracts of Countryside and Rights of Way Act open access land within the stated radius, including Side Fell to the West and White Side and Deer Hill in the Kielder Forest Park to the East.
RAF Spadeadam covers the biggest area of any of the air force’s bases in the UK. It was also the test and launch site for Britain’s aborted Blue Streak missile project.
A further jamming exercise will take place north of the Brecon Beacons national park around the Sennybridge Training Area in June.
Signals within 5km (2¾ miles) of Dixies Corner may be affected by the military exercise. There are several rights of way on hill and forest tracks in the area, on the Mynydd Bwlch-y-Groes.
The jamming will go ahead between 9am and 6pm on the following dates: 11 to 15 June; 18 to 22 June; 25-29 June.