LNB (low noise block) (Down converter - it converts a whole band or block of frequencies to a lower band) This is the bit that points at the dish on the end of the arm or arms. It receives the signal and sends it to the receiver.
They come in many different types but the main type is universal. The LNB has a built in switch to receive both Horizontal and Vertical signals from the satellite. They cover a range of frequencies from low to high and may have many outputs.
Ideally the LNBs should match your dish so that the internal antenna of the device has it's exact focal point in the centre of your dish.
If the dish and LNB are not matched you may not be getting the best from your set-up. With satellite using higher output signals (50-60 Watts) with high gain and low noise figures it is not as important as it used to be to match the LNB to the dish.
If the LNB is seeing less of the dish that it could you will not be collecting all the signal from your dish, If it is more it may be collecting unwanted noise from any warm object like the sky or wall behind the dish. Most LNBs are now positioned 'offset' minimising the amount of signal obscured by the older 'prime focus' LNB mounts.
The smaller the dish the more important the match is that is why the Sky mini dish comes complete with a matching LNB.
Early satellite television was broadcast in C-band radio -- radio in the 3.4 GHz (gigahertz) to 7 GHz frequency range. Digital satellite transmits in the Ku frequency range (12 GHz to 14 GHz ).
Universal LNBs can receive signals from 9.75 GHz low band and use a 22 kHz tone at 0.5v p-p to switch to 10.6 GHz high band.
LNBs also have a noise figure associated with them but these figures are subjective and can be misleading. Generally speaking the lower the noise figure the better the LNB.