This report by the National Radiological Protection Board (NRPB) Advisory Group on Non-ionising Radiation (AGNIR) gives advice on possible health effects of Terrestrial Trunked Radio (TETRA). It was prepared, at the request of government, after the Independent Expert Group on Mobile Phones (IEGMP) recommended in May 2000 that ‘as a precautionary measure, amplitude modulation around 16 hertz should be avoided, if possible, in future developments in signal coding’.
The TETRA system is used for commercial applications, by emergency services in the UK, and in a number of other countries that use a network of base stations to serve terminals, that are either vehicle mounted or in the form of separate handsets. Its operation results in power modulation of some of the radiofrequency signal at a pulse frequency of 17.6 hertz.
It is recognised that calcium plays an important role in many biological processes, especially in the function of nerve cells. Moreover, as the IEGMP pointed out, there is evidence that radiofrequency fields, amplitude-modulated at about 16 hertz, may influence the leakage of calcium ions from tissues. However, findings have been contradictory: they are more uncertain for living than for non-living tissue, and no associated health risk has been identified.
It is notable that the signals from TETRA base stations are not pulsed, whereas those from mobile terminals and repeaters are. Although areas of uncertainty remain about the biological effects of low level radiofrequency radiation in general, including modulated signals, current evidence suggests that it is unlikely that the special features of the signals from TETRA mobile terminals and repeaters pose a hazard to health.
The Home Office TETRA health and safety studies include a response to this document.