The LNB is a combination of Low-noise amplifer, block downconverter and IF amplifier. It takes the received microwave transmission, amplifies it, downconverts the block of frequencies down to a lower block of intermediate frequencies where the signal can be fed to the indoor satellite TV receiver using relatively cheap cable.
The signal from the dish is picked up by a feedhorn and is fed to a section of waveguide. In this waveguide a metal pin, or probe, protrudes into the waveguide at right angles to the axis and this acts as an aerial, and feeds the signal to a printed circuit board in the LNB.
The LNB is usually fixed on the satellite dish framework, at the focus of the reflector, and it derives its power from the connected receiver. This phantom power is sent “up” the same cable that carries the received signals “down” to the receiver. The corresponding component in the transmit link uplink to a satellite is called a Block upconverter (BUC).