Radio waves are and will be analog in the form of oscillations.When we talk about digital broadcasts, we are therefore talking about modulating, or shaping, the waves so that they contain digital signals.The dominant way of doing it is through QAM (Quadrature amplitude modulation) or by shaping the wave height (amplitude) of two carrier waves that are sent 90 degrees out of phase with respect to each other (quadrature).One can have few or many possible signal combinations in QAM.Many provide a high bitrate, but also make the signal more sensitive to noise.The highest figures are therefore found in cable TV, where the waves are little affected by noise.The lowest QAM numbers are used in satellite TV, while terrestrial networks use slightly higher values.As the standard evolves with new technology, such as better error correction, higher QAM numbers can be used to get higher capacity in each channel.An important difference, which has nothing to do with the various standards, is that the terrestrial networks, both used for phase and mobile devices, are severely limited in terms of available bandwidth.The same is not the case when the broadcast is via cable (coax or fibre) or via satellite.There are many DVB standards.The most important for TV reception are DVB-T, DVB-S and DVB-C.The letters T, S and C stand for Terrestrial (ground network, received with an ordinary antenna), Satellite and Cable respectively.And as if that's not enough, these standards are constantly evolving.They are also not necessarily backwards compatible, so new hardware is needed to accept them.This means that it is no longer so easy to build a digital receiver into the TV because the TV manufacturer does not know which signal source the users have at home.Is it terrestrial, cable TV or satellite?On top of it all, the vast majority of signals are encrypted and preferably with various encryption technologies.But there is hope!There is no way back to the analogue world, and the added value comes in the form of a much lower price per channel and higher quality of the broadcasts.The most talked about technology at the moment is DVB-T.We have received a new digital terrestrial TV network to replace the old analogue.The first edition of the standard came out eleven years ago and has become the most widespread standard for terrestrial networks in the world.There are now more than 60 million DVB-T terrestrial receivers in over 35 countries.In the old analogue network, a TV channel occupied a bandwidth of 8 MHz.The same bandwidth is used in the digital network, but instead of containing the old PAL TV signals, digital signals are modulated in.The standard allows for several different modulation techniques, ways of correcting bit errors and other parameters, which the various countries can choose from in order to optimize the network for local conditions.In this country, the combination of parameters gives a net capacity for TV channels of just over 20 Mbit/s on each of the five channels.Within this capacity, up to eight digital TV channels are broadcast.They are put together in a so-called multiplexer (MUX), which ensures that the various channels get the capacity they need depending on the content (statistical multiplexing).A talking head needs little capacity compared to a football match.But if all the channels on the same MUX were to broadcast football, the quality would be very poor.The Norwegian digital terrestrial network has three operational MUXes, and there will be two more from 2010. There is room for two more, but it has not been decided that they will go to television.Unlike in most other countries, mpeg4 compression is used for the video signals in the Norwegian terrestrial network.It is more efficient compression than traditional mpeg2 and gives us slightly better space for more TV channels.Technological development does not stand still, and these days the final touches are being put on the new DVB-T2 standard, but it will probably take a year or two before the equipment appears.It opens up new modulation techniques, better error correction and other improvements that together increase capacity by between 40 and 60 percent.It would of course be manna from heaven (almost literally) to have such a large capacity increase in the terrestrial network.Unfortunately, all subscribers will have to change receivers because T2 requires new electronics.DVB-S is the variant that has been with us the longest in this country.The roll-out of digital satellite television to replace the analogue broadcasts started ten years ago, and in 2002 analogue satellite television came to an end.A satellite transponder is at 27 MHz.This gives a frequency range of around 38 Mbit/s.The new DVB-S2 standard has already been adopted for broadcasting HDTV.New coding and modulation techniques as well as better error correction have made it possible for Telenor to increase the bitrate to 55 Mbit/s.The increased bitrate, in addition to the fact that the television signals are encoded in mpeg4, gives much more space to send HDTV where each channel needs up to 20 Mbit/s just for video.Cable TV has also been developing for a long time.The large Norwegian distributors started digitization eight years ago, but because the new networks with modern cable infrastructure have such enormous capacity, they will continue to broadcast analogue for many years to come.It allows subscribers to connect to the old (and new with analogue receivers) TVs without any kind of box, although the quality is much worse.With today's DVB-C standard, it is possible to receive 50 Mbit/s on an 8 MHz channel.Although there is no shortage of space in a modern cable network, the next standard edition will be even more efficient and significantly increase capacity on each channel.DVB-H is the most current standard for sending television to mobile devices such as mobile phones.Several European countries have trial broadcasts with DVB-H.The standard is based on DVB-T, but takes into account that the broadcasts must be received by mobile battery-powered receivers.To reduce power consumption, the content is sent in pulses so that the receiver can switch off between each pulse.Such a receiver is on only about 10 percent of the time.The problem with DVB-H is that a rollout across the country will require a very large number of transmitters and will be very expensive.Especially because many transmitters will be needed to get good coverage indoors and for cars.It can be difficult to get an income that can finance a development in a large and sparsely populated country like ours.Moreover, this will require a lot of valuable capacity in the VHF frequency range.An interesting new variant is DVB-SH which transmits directly from satellite to mobile receivers.This standard can make it much cheaper to build out the network, which then only needs to be reinforced with complementary ground transmitters to get indoor coverage in important areas.Source: Chief Technology Officer at Telenor Satelitte Broadcasting, Torkel Thoresen