The choice between the three options, a single-satellite, multi-LNB or motorized dish, has some impact on the rest of the equipment. Of course, once you have made the decision that you want 'digital, UK, English', or 'motorized, all channels possible', and the price range, you will normally just go to a local dealer-installer and ask him to put up a complete package that will give you that. The dealer will then make sure all the elements fit together, and will accommodate for local conditions. That is definitely the preferred method for digital installation, as the installers have equipment that will ensure a more precise and better installation than you can easily do yourself. So, you do not need to have any further information about the various parts of your satellite's set-up. However, in case you are interested in what components go into the deal, we will briefly describe the major elements, which are:
Thus, the satellite setup has two parts : one on the wall outside of your house, and one inside your sitting room next to the TV. On the wall outside or on your roof is the circular dish, 50-100 cm wide. All the dish does is to reflect the signals from the sky into the small box that is sitting, poised on an arm above it and pointing to the centre of the dish. This little, box then is called an LNB ['Low Noice Block converter'], or more colloquially, the 'head'. A cable then transmits the signals from the LNB to the receiver inside.
- The dish itself
- Inside the dish: the receptor 'head' or heads (the 'LNB')
- For multi-satellite installations, ways to switch from one satellite to another
- The receiver inside your house
- The size of the dish is of some importance: the larger the dish, the more signals get reflected into the LNB, and the stronger the reception. How large a dish you need depends on where in Europe you live (the further north, the larger dish), and how weak or strong the satellite signal is (how focused on your country). Most normal is 50-60 cm in the south of Europe, 70-90 in the north. Apart from this, you need not worry much about the dish itself.
- The LNB head itself is of greater importance; a better head will give stronger signals (a 'noise figure', over 1.0 is bad, 0.6 fairly good).
- The satellites send out its signals on particular frequencies (like those of the radio, remember?). The LNB receives these signals and transmit them to the receiver. However, satellite signals are very weak, and are sent on extremely high (microwave) frequencies. There is no way they could survive transmission through a cable in their original form. The LNB therefore converts them to a lower frequency that the cable can handle. The receiver must thus match this 'down-shifting' to locate the correct frequency for each channel.
- The actual frequncies used by TV satellites are in a region of c. 10,700-12,700 MHz. The LNB shifts them down by a factor of around 10,000 MHz, so that an original signal at e.g. 11,200 Mhz is sent down the cable at 1,200 MHz. This figure of 10,000 is known as the 'LO' (Local Oscillator) setting; and it is this that the receiver must be aware of to find the channel.
However, there is a further twist: even with the downshift, this creates a range of about 2,000 Mhz from the lowest to the highest frequency. That is also beyond the capacity of TV cables to handle; about 1,000 is the maximum span possible. So, an LNB can have two or more LO settings, which it switches between at the request of the receiver: E.g. a 'low' LO of 10,000, which it uses for channels in the frequency 10,700 - 11,700, and a 'high' LO of 11,000 used for 11,700 - 12,700 MHz, so that it is only a frequency between 700 and 1,700 Mhz that is in either case sent down the cable. Again, the receiver and LNB must communicate these settings between them, so that the receiver finds the channel.
- This was a major issue of concern in older days (five years ago); you had to be careful what LNB you installed and that it matched the receiver. Happily, in recent years, most analogue and all digital receivers have settled on a common standard, known as 'Universal LNBs' (they have two LOs of 9,750 and 10,600 MHz). So, if you have a modern analogue installation and want to upgrade to digital, check that you have a Universal LNB; if so, it will work fine with the new. If you buy a new satellite setup of whatever kind, you need not worry about the LNB.
- Another element that was more cause for concern earlier than now, is 'polarization': some of the satellite's waves are sent 'horizontally', others 'vertically' (to be able to cram more signals without overlapping). The LNB adapts to the polarity of each channel, according to a request from the receiver. Earlier, this was handled in different ways, often with separate cables. Universal LNBs have again standardized this, and handles everything on the same cable: It reacts to a tone (sent on 22 kHz) to switch between low and high LO, and electric voltage (13 or 18V) to switch between horizontal and vertial polarity. Thus, any modern receiver that can work with Universal LNBs handles both these settings without any intervention or care from your side.
- However, unfortunately universal LNBs no longer have the option for fine-tuning the polarity (skew), which older LNBs had. This may however not be much of a problem for digital reception, except sometimes on a motorized dish when you move it too far off too the west or east; the French analogue channels are also notorious for skew.