The radiation from TETRA (otherwise known by its brand name 'Airwave') is, by its very nature, sometimes difficult to identify. It is a system that is used by the military and the emergency services. Coastguard stations also use it. The TETRA network covers approximately 99% of the UK and there are some areas that seem to have more intense signals, such as those located within a few miles of military zones and bases.
TETRA transmitters are often found together with TV transmitters, and sometimes they share the same mast. They are also often located on, or close to fire stations, police stations and hospitals.
There are plans to decommission TETRA and migrate users over to the new Emergency Services Network (ESN), which will operate on the existing 4G mobile network. Work was to begin phasing out TETRA over a three-year period, starting in 2017, but unfortunately this was delayed.
The latest media reports suggests that TETRA may not be decommissioned until well into the early 2020s. Perhaps one of the reasons for the delay may be that the nationwide coverage of 4G is not sufficient to operate the new ESN (coverage of 3G and 4G in the UK is said to be only 97% - less than that of TETRA).