TETRA (Terrestrial Trunked Radio) is the communications system used by many of the emergency systems in the Ireland and the rest of Europe. It has a number of communication advantages which are particularly suited to emergency services, such as,
- The use of lower frequency which provides very high levels of geographic coverage.
- Very fast call set-up. (A one to many group call is generally set-up within a half second compared with the many seconds).
- TETRA is built to connect one-to-one, one-to-many or many-to-many. (Unlike cellular technologies, which only connect one-to-one).
- The system contains several built-in mechanisms and special protocols to ensure communication success even during overload situations.
Both the handsets and base-transmitters are more powerful than normal cellular ones “to give a more secure mode of communications”. The TETRA system emits electromagnetic pulses at 16.7 Hz, a frequency which research has found may affect brain activity. It transmits at around 400 MHz (some services use 900 MHz), which most current shielding materials are not particularly effective at shielding against. Some people find they will react to TETRA equipment but not to other telecommunications systems. In Ireland TETRA technology is used by the Garda Siochana, the Fire Services and the HSE National Ambulance Service.