Satellite basics


This is a brief explanation of the difference between satellite and terrestrial reception

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If you have a satellite dish already and want to add a PC card or Freesat receiver, it's not quite as straightforward as splitting a terrestrial TV aerial.

For Freeview, you can simply use a splitter - and many PVRs have one internally; just one cable can feed both the tuners in a PVR, though there may be a small loss of signal. Since the TV aerial is just a lump of metal, it doesn't care what you plug it into, or how many devices there are. But the satellite world is very different.

At the end of your satellite dish arm is the Low Noise Block downconverter, or LNB. This shifts the frequencies of broadcasts and then sends them along the cable to the tuner in the receiver. And unlike a TV aerial, it's not passive; it has to be set to high or low band, and vertical or horizontal polarization, by the receiver. So two tuners on the same LNB would be forced to watch channels in the same band and polarisation.

For each tuner to have complete choice of available channels, it needs its own LNB and connecting cable. You can buy a dual LNB, which is one unit to mount on the satellite arm, containing two independent outputs, and quad or octo ones too, with 4 or eight. A twin tuner PVR will need two connections - so on many installations, a quad LNB is standard now, to allow for additional receivers.

For more options, a Quattro LNB has four fixed outputs - one for each combination of band and polarisation - and is used with a multiswitch. These work a bit like a TV aerial amplifier, allowing many outputs - 12, 16, or more - and look at the signal from the tuner, then connect that tuner to the appropriate signal from the LNB, allowing full channel choice on every connection. A fifth input on most multiswitches allows them to be used to pipe terrestrial TV around the home too.

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