The LNB is located at the focal point (in the nose cone) of the satellite dish antenna and amplifies the very weak received satellite signal approximately 1000 times, then converts the received microwave satellite signal to a lower frequency so that not as much signal will be lost in the coaxial cable between the dish and the receiver.
There are two main types of LNBs. The most popular type is the LNB that is attached to a feedhorn and uses an external servo motor to turn a probe inside of the feedhorn to select the polarity of the desired channel. The other type of LNB is actually called an LNBF, where the LNB and feedhorn are one unit and the polarity is switched when the receiver changes the voltage (either 13 or 18 volts) going to the LNBF at the dish. Depending on what voltage is sent to the LNBF by the receiver, either the horizontal or vertical antenna probe inside the throat of the LNBF will be selected. LNBFs are also used on the smaller DBS satellite systems.
Within the standard LNBs, there are two types: consumer-grade and commercial-grade. The biggest difference between a consumer-grade and commercial-grade LNB with PLL (phase locked loop) is the amount of frequency drift that the LNB has. Frequency drift occurs when the air temperature changes out at the LNB. All LNBs have a certain amount of "drift" but PLL LNB's have much less drift than consumer-grade LNBs. Digital channels are more sensitive to this frequency drift, and it is highly recommended that a PLL LNB be used on any high quality TVRO satellite system, whether it be a residential or commercial installation. The following illistrations from California Amplifier show the difference in drift between and a consumer-grade and commercial-grade PLL LNB.