A BUC (Block Up converter) is used in the satellite communications uplink，
A LNB (Low Noise Block Converter) is used in the satellite communications downlink.
BUC (Block Up converter) It converts the radio signals from a lower frequency to higher to transmit to the satellite. BUC used in remote locations are often 2W or 4W in the Ku band and Ka band, 5W in the C band.
LNB (Low Noise Block Converter) It receives the radio signals from the satellite and converts them to a lower level (IF band or L band) sent to the cable modem.
An example of a system utilizing both a BUC and a LNB is a VSAT system, used for bidirectional Internet access via satellite.
