From a headend or digital header, the signal is implemented that will allow the transmission of the signal and its value-added services. But what features should a header for digital television have and how is it built?
According to Javier León, Motorola Country Manager, a headend or digital header is the starting point of a cable television system, whose degree of complexity depends on the services provided by the network. That is, a headend allows to pass the analog television information to the digital system and then send it by some means, which can be cable, satellite or air. And to distribute these unidirectional television signals (analog and digital) there is a series of television reception equipment, either terrestrial, satellite and microwave, as well as links with other headers or production studios.
Processing those signals, generated locally (internally) or received by air, satellite or microwave (external), requires specific steps.
If it is done locally or internally, it is based on a video source, that is, a VCR, a video server or a video recorder, and through an encoder the signal is digitized, and passes through a multiplexer that groups several channels into one. This signal is encrypted for network security and then modulated to an IF frequency, transported to a converter and finally to the RF to be placed on the channel that the operator wants.
In case of processing a signal externally, received by air, by a satellite receiver or by microwave, the signal is sent to a channel processor whose main function is to tune, amplify and convert the output, and then send this signal to the network. The satellite signal is received by a satellite dish, amplified and converted by an LNB and tuned by a satellite receiver. A cipher, a modulator and a VP converter are used in this process to finish digitizing and 'multiplexing' the signal. On the other hand, the resulting audio and video will be modulated on the corresponding channel. Each of these channels is combined at the output to be sent by optical fiber through a laser.
It is worth noting that the digital video, audio and data signals that make up digital television channels are encoded according to the MPEG (Motion Picture Expert Group) standard. On the other hand, the analog signals are organized for transmission by means of the cable and are 'multiplexed' in frequency in the band between 55 and 870 MHz or up to the giga.
Achieving a digital signal through a header or headend allows a bandwidth saving of 8 to 1, improves the audio (in the analog signal you have stereo sound while in digital you can work sourround of 5.1). In addition, in the case of video, the digital signal is maintained with the same quality that came out of the header.
Other advantages of a digital header are reflected in the monitoring of the network and the possibility of supervising its operation. This control system is very important, due to the new architectures and the sophistication of the new services that are transported on digital television, since a high reliability network is required. Beyond these technological benefits are the tariffs and control of the services provided to subscribers. With this type of signals, piracy is drastically reduced. This last factor allows us to affirm that the investment in the updating of the network is paid with what is obtained by the reduction of piracy. Something like "save money by investing in digital".
