BUC - block up converter is a device used in bidirectional satellite transmissions. It is used to transmit the signal from the dish to the satellite. It converts the signal to the transmit frequency and amplifies it before transmission. Modern BUCs convert from the to , and . Older BUCs convert from the 70 MHz band to
Most BUCs use Phase-Locked Local Oscillators and require an external 10MHz reference frequency to maintain the correct transmit frequency. The 10 MHz reference frequency is usually sent on the same feedline as the main carrier. Many smaller BUCs also get their DC current over the feedline, using an internal DC-block.
Lower or higher powers are associated with less or greater bit rates. At different bands different powers are needed. For example Ku band BUCs are available with 0.5,1,2 or 4 watts. C bands BUCs are available with powers of 2 or 5 watts.
BUCs are generally used in conjunction with . The BUC, being an up-converting device makes up the transmit side of the system the LNB makes up the receive side. An example of a system utilising both a BUC and an LNB is a VSAT system used for Internet access via satellite. | 
