This page is unashamedly aimed at people who simply don't have the first inkling of what satellite TV is all about and who view it as one of the Black Arts. There is also a glossary at the end, which is where you'll find the main jargon buster.

Conventional television programmes are sent out in analogue (wave) form via transmitter masts strategically placed around the country to provide as wide a reception area as possible. Aerials on houses (or caravans) pick up that signal and pass it down to the television which amplifies it and converts it into vision and sound. An immediate drawback is that there has to be a direct line-of-sight between the transmitter and the receiving aerial. The signal will make it through buildings and trees to some extent but not through a hillside. Even with relay transmitters, inevitably there are parts of the country where the local terrain prevents a signal reaching people's aerials and the result is poor or even non-existent reception. Another common problem is the non-availability of Five which because of possible interference with adjacent channels in some areas has to transmit only on low power and even, in some areas, not at all.

Digital satellite technology provides a relatively new method of transmitting the programmes. The satellite system sits 22,300 miles above the equator - a height at which its orbital speed precisely matches the rotation of the earth. The result is that the satellites appear to hover over the same point of the earth's surface and therefore an earth-based receiver, once correctly aligned, will always point towards them. This is known as a geostationary orbit. The concept of geostationary orbits was first worked out by the scientist and sci-fi writer, Arthur C. Clarke, and that area of space over the equator is now called the Clarke Belt in recognition of his work.

The satellites we're interested in are the system known as Astra 2. Astra is a trade mark of a Luxembourg-based company, Société Européenne des Satellites, which builds, launches and operates a fleet of satellites, grouped into 3 distinct systems, Astra 1, Astra 2 and Astra 3. The only system relevant to this website is Astra 2 which is the one used by Sky and the terrestrial channel operators like the BBC. Sky doesn't actually own the satellite system any more than the BBC or any other broadcaster does, it merely rents space on it.

There are 4 satellites in the Astra 2 fleet. They are 2A, 2B, 2C and 2D and between them they carry all the channels provided by the Sky service including the UK terrestrial channels. [And before anyone writes to tell me about Eurobird, I do know about it, but it's an unnecessary complication for the sake of this particular discussion.] All the Astra satellites have directional aerials which beam their signals towards Europe and although there is some variation in the amount of spread it does mean that virtually all parts of the UK, and many parts of Europe, can pick up the signals. All the beams cover the British Isles but in other parts of Europe that isn't the case. You'll find therefore that certain channels are no longer available to you as you travel beyond the range of the particular satellite that carries them.

Other satellite systems dotted around the equator beam their signals to other parts of the world, so virtually every country in the world is capable of receiving a satellite service of some sort.

Anyway, back to Astra 2. (Hope you're still paying attention at the back, there'll be a test later!) The satellite signal itself is fundamentally different from that used by terrestrial analogue transmitters in 2 important aspects. First, it is many many times weaker than a terrestrial signal and therefore it needs a parabolic dish to collect it and focus it on to an antenna, a bit like the radio telescopes at Jodrell Bank. Second, even if the signal were strong enough to drive a television, it still wouldn't work because it's in the wrong format. Traditional television signals are transmitted in analogue form (as radio waves) but digital transmissions are sent as a high speed stream of 1s and 0s which most current models of television can't work with.

So in order to receive satellite transmissions, you need some extra kit. The 2 main items are the dish and the digibox. (Strictly speaking 'digibox' is a Sky trademark but it's become a bit generic these days, like hoover or xerox). The dish collects the very faint signal from the satellite and focuses it on to the antenna. The antenna isn't called an antenna though, it's called an LNB ('low noise block down-converter' since you asked!). The LNB then sends the signal down the cable to the digibox, sometimes referred to as a set-top box or STB because they were originally designed to sit on the TV rather than underneath (not that that matters - you can stick it anywhere you like).

The digibox is a receiver/decoder which picks up the signal from the dish, amplifies it and then converts it into analogue format before sending it on to the TV. It also unscrambles any encrypted signals, such as the UK terrestrial channels and the Sky subscription channels, based on information stored on a viewing card. The viewing card is a smart card with an embedded computer chip (like Chip 'n' Pin credit cards). The chip stores all the information relevant to your Sky subscription if you have one, and your postcode for decoding the correct regional BBC1 and ITV1 for example.

A digibox will work without a viewing card but you won't be able to see any of the encrypted signals, only those that transmit in clear such as the BBC, Sky News and various shopping channels. The BBC, ITV and Channel 4 are all free-to-air and can be viewed by any satellite receiver without a viewing card. Five is currently (October 2008) encrypted but that is likely to change before the end of the year.

The television transmission system used in the UK for the terrestrial broadcasting of colour television programmes is called the PAL system. (See the glossary for what these acronyms mean.) PAL is used in many other parts of Europe and across the world, but there are other systems in use. America for example uses the older NTSC system which we Brits reckon stands for 'Never Twice the Same Colour', whilst the French, bless 'em, invented the SECAM system so as to be different from les Rosbifs. All 3 systems are incompatible with each other, so a SECAM television for example won't necessarily work with a PAL digibox or video recorder. Some modern televisions and video recorders are multistandard and will often play NTSC recordings, but not necessarily SECAM recordings.

Digiboxes are designed to sit between the signal collector (aerial or dish) and the television or video recorder. If an aerial cable is present, it plugs into a spare socket on the digibox and the 2 feeds, from the dish and the aerial, are then combined and sent via a single lead to the television or VCR instead of having to keep swapping over whenever you want to watch terrestrial TV. The digibox doesn't modify the aerial signal in any way; it simply sends it straight through to the output cable along with the decoded satellite signal.

Although this website is concerned primarily with satellite broadcasting, I should point out that satellite is not the only source of digital television. Digital television programmes are also available via a cable connection or through your traditional aerial. Like satellite transmissions, both require a digital tuner to decode the signal. The technologies are all incompatible with each other - you can't receive a satellite signal with a cable box for example. Cable TV is carried in this country by Virgin Media and is available to anyone who lives in an area that has already been 'cabled'. It also carries a telephone service which is usually cheaper than BT's and in many areas of the country it will provide a broadband internet service as well. Cable services differ from either of the other two in that there is not a free-to-air option. Even if you only want the basic set of programmes, you still have to pay a monthly rental and the receiver remains the property of the cable company. You cannot purchase it outright nor does it become your property at the end of a contract period.

Digital television through your aerial ('Digital Terrestrial TV' or DTT) operates under the name Freeview (not to be confused with free-to-view which refers to encrypted but non-subscription satellite channels). Decoder boxes for Freeview are now available in the high street at prices as low as £20. In addition most new TVs now have digital tuners for Freeview. Such sets are able to receive Freeview without the need for an additional set-top box. For digital services other than the one the set was designed for, the appropriate set-top box is still needed. Panasonic has a range of TVs designed for Freesat (but not for Sky), but as far as I know, no manufacturer has any plans to build TVs with a built-in cable tuner.

Freeview still cannot provide the same coverage enjoyed by traditional analogue transmissions because until they are finally switched off, Freeview can't be transmitted at full power. It might be necessary therefore to upgrade your existing aerial in order to get an adequate signal and some parts of the country can't get it at all. [As a point of general interest, the analogue signals are due to be progressively switched off between 2008 and 2012. The Government has said that the impact on viewers will be fairly minimal because around 70% of all households can already receive digital TV. That might be true but it's an argument that at best is naive and at worst downright misleading. The majority of those households have a single set-top box serving a single TV, but once the analogue signals are switched off each TV and video will require its own separate set-top box, which in turn will require its own separate power supply and connection to an aerial or dish. Families with TVs in bedrooms and maybe even in separate rooms downstairs will need to think seriously about how they will manage the changeover. Further details are on this separate page.]

Obviously cable TV is irrelevant to caravanners and is included here merely for completeness. Theoretically, Freeview might be of interest though I would have thought your chances of getting a signal with a touring aerial are slim (although I am aware that some people have managed it to some extent with a standard Status aerial). In any case it would be no better than analogue television once you cross the Channel. All 3 digital platforms carry the 5 terrestrial channels, but vary in the choice of other free-to-air and subscription channels they carry. Freeview in particular does not offer a subscription service, although TopupTV runs a pay service alongside the free channels that Freeview provides. Note that many existing Freeview boxes can't receive TopupTV because they don't have a viewing card slot. If you're interested in receiving TopupTV, make sure the receiver you buy has a suitable slot. Details about TopupTV for anyone who's interested are at www.TopupTV.com.

This is a bit tricky to explain because to the vast majority of people in Britain, satellite TV is synonymous with Sky, but here goes.

Sky developed the first successful satellite system in this country and by effectively giving away digiboxes free of charge, they swept aside any chance of a commercial rival getting a toehold. In Europe, that's not the case and people there have access to hundreds of different models of satellite receiver (in much the same way that we here in the UK can buy Freeview boxes from virtually any store and supermarket).

The thing about Sky boxes is that they operate in a very simple way - the installer fits the dish and connects the digibox to the TV, and the householder then selects any channel from a pre-installed and standard Electronic Programme Guide (EPG). The way in which the digibox works is identical regardless of the manufacturer, even down to a single design of remote control. Other makes of receiver don't have access to that EPG and will have one of their own but it might be subtly different from one make to another. The method of tuning the receiver will be different as well, just as you have to read the manual whenever you buy a new TV or video to find out how to tune it in.

Strip away the presentational aspects however, and a Sky digibox works in very much the same way as any other receiver. It picks up a signal from the satellite and converts it into an analogue form suitable for the TV. So if you buy a non-Sky receiver and point your dish at Astra 2, the receiver will pick up the same UK channels as a Sky box. There are then 2 obstacles - first, that it won't be able to unscramble any encrypted signals and therefore is no use for Sky's subscription channels and second, you will have to tell it what frequencies you want to watch. Most non-Sky receivers have some kind of automatic scanning of the frequencies and you'll then be presented with a list of available channels. Obviously that only has to be done once unless other channels come on stream as happened in 2005 with ITV4.

In May 2008, the first attempt to knock Sky off its perch arrived with Freesat from the BBC. The BBC, jointly with ITV, launched its own free satellite service, equivalent to Freeview. It is called Freesat and comprises a series of branded receivers to a defined standard. Initially only 2 manufacturers (Alba and Humax) are making Freesat boxes (with Panasonic building Freesat-integrated TVs) but that will change - any other manufacturers can build their own receivers if they want, provided they conform to the Freesat specification, which should force the price down considerably. Again there's an obvious parallel with Freeview. Indeed in July 2008, there is news that Metronic will be launching its own Freesat receivers. All the UK channels will continue to transmit from the Astra 2 satellite system so it won't matter whether viewers use a Sky or a Freesat box (or any other make of box for that matter), and all dishes will continue to point the same way.

Satellite beams

Every so often I receive an email such as this one where the writer is obviously confused by the concept of multiple satellite beams, so I've included it and my answer here:

Can you help me with some information I can not seem to get my head around. Astra 2d is used to broadcast bbc itv 4 5 etc. Astra north and south does not?? If a sky box is default to the north beam where does it get the bbc's etc from, when in France Spain Germany where does it get the bbc's etc from is it astra 2d or astra north and south. If the British station signal is beamed by astra north and south the reception throughout France and Germany should be readily available with a relatively small dish size, this is where I think I am missing the point and I hope that you will be able to enlighten me.

It's the thing that confuses most people and I still struggle to find a way to explain it adequately.

Basically there are 4 satellites in the Astra 2 system, transmitting several separate beams between them. Each channel is transmitted on one, and only one, of those beams. The beams overlap on the ground to some extent (crucially over the UK of course!) but there are parts of Europe where they don't.

The north beam carries the default transponder (frequency if you prefer) which Sky digiboxes are programmed to look for when they're first switched on. The beam also carries a number of Sky channels.

The south beam carries most of the other Sky channels including Sky News, and also a number of independent channels such as the History Channel, etc.

The 2D beam carries the BBC, ITV and Channel 4 and a few other channels.

So how does a Sky digibox work? Well, when it's first powered up it searches for the default transponder and downloads from it the EPG (electronic programme guide). In normal operation, that's the only purpose the default transponder has. After that, if you choose a particular channel, say BBC1, the digibox knows from its onboard software which frequency to look for from all the frequencies transmitted by Astra 2. It doesn't matter at that stage which beam the channel is on because your dish is picking up signals from all 4. All it has to do is identify the correct one to use, just as a TV or radio will select the right frequency from the various analogue signals coming from your local transmitter.

In the UK, the process is completely transparent because the 4 beams cover the country more or less equally well. However as you travel away from the UK, that's no longer the case so you'll find that some channels are more difficult, and ultimately impossible, to pick up. You can put off the evil moment by using progressively larger dishes but eventually one or more beams will become too weak to pick up and the channels carried by them will disappear.

In southern Europe you can have the situation where the north beam, and therefore the default transponder, can't be received. However there is a limited EPG carried on the south beam so by altering the default to one of the south beam transponders, that one can be downloaded and the digibox will still work. That EPG is limited in carrying only a couple of days of forward planning instead of the normal 7 day schedule.

Here lendeth the lesson!

Glossary of terms