Walkers and outdoor enthusiasts are being warned of imminent jamming of Global Positioning System signals in the hills of mid-Wales.
Ofcom, the Government’s official radiocommunications body, said GPS jamming will occur for two weeks starting next Monday, around the Sennybridge military ranges in Powys.
The jamming will be suspended at weekends.
During the exercises, civilian GPS units are likely to be affected between 8am and 4pm within 5km (3 miles) of Dixie’s Corner, grid reference SN 873 365, and walkers and other outdoor fans will have to rely on conventional map and compass navigation.
The jamming will take place between 24 and 28 September and 1 and 5 October and will affect both the L1 and L2 navigation bandwidths.
There are several rights of way on hill and forest tracks in the area, on the Mynydd Bwlch-y-Groes.