The low noise block (LNB) converter on a satellite dish receives and amplifies the television, radio or data signal before sending it down the output cable to your satellite receiver.
The satellite dish collects the original signal and focuses it at the LNB, which is fixed to the dish with a protruding arm. The LNB converts and boosts the high-frequency satellite signal to a much lower frequency, suitable for the output cable and satellite receiver. Without an LNB, signal loss would be so great that it would be virtually non-existent by the time it reached your satellite receiver.
"Multi-satellite" systems may include a dish with more than one LNB to receive radio and television channels from multiple satellites. You can add extra LNBs to many single-system satellite dishes to receive programs from additional satellites.
An LNB may also be called an LNC (low noise converter) and, less commonly, an LND (low noise down converter), but "LNB" is the most widely used term.