Tetra and digital radio services
From RF side, tetra-and trunked radio networks operate in the same way as the publically accessible mobile communications networks
Although tetra-and trunked radio systems employ major functional elements, which are also used in public mobile communications applications such as GSM, UMTS or LTE, they also offer additional functionality such as point-to-multipoint connections and additionally work in other frequency ranges. In addition, the numbers of the terminals are several orders of magnitude lower than for public mobile communications, because only relatively small teams of railway-, police-, fire-service- and emergency-service workers, etc., operate in tetra- and trunked-radio systems. On the RF side, tetra-and trunked radio networks operate in the same way as the publically accessible mobile communications networks: after the data processing on the transmitter side of mobile communications base stations for GSM, UMTS, LTE, etc., the digital data stream next reaches a very fast DAC and is then sent as an analog signal by cable to the remote radio head or to tower-mounted amplifiers, where special LDMOS transistors, which are particularly suitable for RF, amplify the signals, in order to forward them to the antenna. On the receiver side of the base stations an LNA initially amplifies the RF signal before it is then transferred via PLLs and particularly fast ADCs from the analog RF domain to the digital domain.
