The elements described above are common to all satellite dishes, whether you go for a single, or a multi-satellite set-up. If you want to watch more than one satellite, you have some extra elements, depending on whether you go for a motorized or a multi-LNB installation.
The choices you have to make, therefore, mostly concern the equipment outdoors: a single or multi-satellite setup? if the latter, fixed-dish with many heads or motorized with one? if the former, DiSEqC and what version? If the latter, what kind of motor?
- If you go for a motorized dish, you only need one LNB head which has the frequency span to cover all used on 'your' satellites. The motor is attached to the dish, and should be goverened by the receiver inside, so that when you choose a channel, the dish will automatically move to the correct position in the sky. Thus, the receiver must be able to talk to the motor. Motors are mostly of two kinds, the older 'actuator' motors, and the newer 'DiSEqC' standard. Make sure that the receiver is able to run the motor you have (otherwise, you may need a separate 'interface' between the motor and the receiver to make the connection). Motorized dishes are more complex to install, so you would certainly want a professional to set it up.
- If you instead go for a fixed-dish multi-head system, you also have to consider the size of the dish. Each of the heads will be pointed at (or, actually, directly away from) its own satellite, thus at a slight angle from each other and not at the centre of the dish. That means it cannot receive signals reflected from the total area of the dish. So you must compensate by installing a slightly larger dish than you would with a single head, to let even the most off-centre head receive enough signals for good reception.
- Each head will be pointed away from each other by as many degrees as the satellites are apart in the sky. The head can use signals reflected from within a circle centred around the focus of the LNB. So if the LNB points to a spot five cm off the centre of an 80 cm dish, then its reception is that of a 70 cm dish (5 cm radius=10 cm diameter). If you need a 70cm dish for good reception from each satellite, you will have to install one of 80cm to cover both. Commonly, multi-satellite dishes have a maximum span of about 20 degrees from the western- to the eastern-most satellite it can catch (the maximum angle of the LNBs to the dish), i.e. from Astra 1 to Thor or from Astra 2 to Hotbird.
- When you have two or more LNBs sitting in the dish, you could of course run one cable from each LNB through your wall in to the receiver. It is rather more practical, however, to merge the signals outside, so that they all run down one cable inside, and the receiver inside then is able to switch to the LNB it wants for each particular channel. The most common way of doing this is with a piece of hardware with the unreadable acronym 'DiSEqC' switch (Digital Satellite Equipment Controller, I think - I tend to pronounce it 'disec'). It is in fact a European standard for how to handle multiple equipment, so what you want is, one, the piece of hardware outside that joins the cables from the LNBs into one (the switch), and two, that your receiver inside has the software to control the switch and pick the right LNB. However, the DiSEqC standard has gone through several generation, and how much the equipment can do, depends on which version of DiSEqC it supports:
- Version 1.0 can handle up to four different LNBs, in some early versions only two.
- 1.1 can handle up to 16 different LNB, more than enough for most of Europe. That is therefore what you should look for.
- 1.2 is different, it is designed for motorized dishes (we mentioned it above), and can control up to 30 predefined positions.
- There is also a version 2.0, this is not much in use yet.