Satellite Dish LNBs
LNBs also known as Low Noise Blocks collect the satellite signal received by your satellite dish and down convert the frequency so it can be transmitted down your coaxial satellite cable. The signal passes down the cable to your receiver where it is decrypted if necessary and converted into the picture and sound that you watch and hear.
On a single LNB only one quarter of the available signals are passed down the cable at any one time to reduce the bandwidth required. Your satellite receiver communicates with the LNB to let it know which quarter your desired channel is on. This is why you cannot split a satellite cable, if you need to have two cables you need to run 2 independent cables from the LNB. This is where twin, quad and octo LNBs come into play. For example an octo LNB acts as 8 different separate LNBs all working independently of each other.
Where you need to have many connections to one dish, as in apartment blocks and flats, the best option is to use a Quattro LNB connected to a satellite multiswitch. The quattro LNB will send each quarter of the signals down a separate cable enabling the satellite multiswitch to act as an independent LNB with up to 32 outputs possible from one multiswitch. Satellite multiswitches can be installed in cascade with amplifiers to allow 100's of connections to just one satellite dish.