Digital To TV brings digital television to Prades
The town of Prades (Oriental Pyrenees, France) has a cable television network on which are distributed analogue terrestrial television and other contents. After the analogue television switch-off process the municipality will not have digital coverage due to its geographical location.
In this context, the people in charge at the company NEXTWAY, which has been designated by the consistory, has chosen the Digital To TV (DTTV) headend of PROMAX as the solution, both for the radio link and for the redistribution of DTT channels on the network cable (CATV) at Prades.
The solution proposed by NEXTWAY is to install a station on a nearby hill, from where appropriate antennas can pick up DTT signals from a remote transmitter. Then, the station can re-broadcast the channels received to the CATV headend, which is placed in the centre of the town.
The radio-link station consists of a receiving antenna, a DTTV headend and three transmitting antennas. Five DTT channels are picked up from the transmitter station “Pic Neulós” by means of the high-directivity receiving antenna. Then the DTTV headend extracts from each channel the digital data (transport stream), correcting all the errors generated during the transmission and modulating the restored data again in DTT format. The DTT signals obtained, which are amplified by the same headend, are broadcasted towards the town through the transmitting antennas.
Radio-link station proposed by PROMAX
The DTTV headend installed as a radio-link consists of three DT-212 units and three DT-722 units. The DT-212 module transmodulates from DVB-T to DVB-T, with capacity for two channels. The DT-722 module mixes and amplifies the regenerated signals.
Three DT-212 modules regenerate 5 channels. In order to optimise the radiated power, the channels are amplified in pairs so are used three DT-722 modules. Each module’s output is directly connected to a transmitting antenna. This arrangement does not need antenna multiplexers and thus prevents the loss of power.
For legal constraints reasons an iso-frequency system is used, that means that the DTT signals are broadcast from the radio-link station on the same frequencies that are received. This requirement forces to place the transmitting and the receiving antenna with precision for maximum insulation and for preventing the signals fed themselves. To further reduce coupling, different polarities are used between the reception and the transmission and also high-directivity antennas.
The top left image corresponds to a radio-link station equipped with the DTTV headend. As has been indicated, due to the iso-frequency system is necessary to avoid coupling by spacing the receiving and transmitting antennas. In order to achieve a better insulation, the transmitting antenna broadcasts towards the town using vertical polarity because the transmitting centre of Pic Neulós broadcasts in horizontal polarity. At the bottom right image pictured the technicians of the NEXTWAY company that have implemented the solution for digital television based on DTTV.
At the heart of the town, about 4 km from the radio-link station, there is the cable network headend (CATV), which picks up the signal by using a conventional Vagi antenna. This CATV headend regenerates the DTT signals by using another DTTV system. Then they are injected into the local cable network, ensuring that all users receive DTT signals with the highest quality.
DTTV system allows restoring each stage of the transport stream, achieving the original quality of the transmission because all errors are corrected.
DTTV system, based on a modular architecture, is the most economical solution to broadcast DTT channels in areas where coverage is lacking or deficient. No matter what is the problem, with the DTTV system there is always an appropriate solution to any need.