Transponder table

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A transponder table is a table with transponder data stored in a digital TV receiver , which is required for receiving or decoding digital television signals. In a DVB signal, the transponder data is embedded in the Satellite / Cable / Terrestrial Delivery Descriptor in the Network Information Table (NIT). There are further descriptors in the NIT, e.g. B. the BAT table for sorting the channels. Often, incorrectly, only the NIT is mentioned, but what is meant are the delivery descriptors embedded in this table. When converting a satellite or terrestrial signal into a cable signal, the transponder data should be converted into a cable delivery descriptor, which is not mandatory according to the DVB standards.

In contrast to analogue reception, digital receivers are dependent on specified parameters for decoding digitally transmitted television and value-added services via cable , satellite or terrestrial antenna . Modern receivers are now also capable of a so-called blind scan . If a valid delivery descriptor table is contained in the transmission signal of a reference transponder stored in the receiver, a station search can be carried out much faster by the receiver, as it contains all reception parameters (frequencies, etc.) of an operator (e.g. Astra ).

In new digital receivers, an up-to-date transponder table or a reference transponder with a valid NIT is usually stored at the factory; some manufacturers offer a constant update of the transponder table via a firmware update as a service. Modern digital receivers offer an automatic update of the channel list. For this purpose, either a new station table is carried out via the Internet (if available in the receiver) or via a reference transponder with evaluation of the transponder table and a subsequent search. The program sequence is retained, as each program is clearly referenced using the parameters Original Network Identifier ( ONID ), Transport Stream Identifier ( TSID ) and Service Identifier (SID). This numerical assignment is also called a DVB triplet. (The assignment to channel names takes place in the Service Description Table (SDT)). In the case of older digital receivers without an update option, an update must be carried out manually, as otherwise the programs of a new transponder will not be found by the receiver during a station search.

With digital television (DVB), the transponders broadcast an NIT with suitable delivery descriptors. To use this, some receivers support what is known as a network search, which first searches through all the transponders that have already been programmed and collects the NITs broadcast there (since the broadcast NITs usually only contain part of all transponders). The receiver then searches through all the different transponders that it has extracted from the NIT and was not yet known to it. There are satellite positions where the NIT does not contain any delivery descriptors, for example on Eutelsat 9A . Even with many smaller cable networks, the satellite signal is implemented transparently, i.e. without adapting the delivery tables. The received signal therefore still contains the frequencies of the original satellite transponder and not the respective frequency in the cable signal. They are therefore unusable in the cable and a network search cannot be carried out.

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