A Low Noise Block converter (LNB) is an active device (amplifier) mounted at the focal point of a satellite antenna. The LNB is normally mounted on a Feed horn that gathers the signal reflected off the dish.
The Low Noise Amplifier receives and amplifies the very weak signals from the satellite, 22,300 miles in space. They are called low noise because they introduce very little unwanted noise into the signal (all amplifiers introduce noise). The block down converter converts the high frequency signals (4 GHz to 12 GHz) down to 950 – 2150 MHz so it can easily be transported on coax cable to the satellite receivers.