The BUC (Block Up-Converter) is part of the transmit chain of the VSAT. It is often located on the feed horn, but if it is a large BUC, it may be located at the base of the VSAT antenna and connected with RF conduits (waveguides). The BUC converts the modem's L-Band transmit signal into higher frequency C-Band signals, then amplifies it before it is reflected off the satellite antenna towards the satellite. In order to perform both of its functions, the BUC is composed of two individual components: the Local Oscillator and the Power Amplifier. The Local Oscillator performs the frequency conversion between the L-Band and the satellite frequency, such as C-Band. The resulting satellite frequency is calculated by adding the L-Band frequency to a number known as the Local Oscillator Frequency that will be stamped onto the BUC. A Local Oscillator Frequency of 4900 MHz is used for a non inverted spectrum, and a Local Oscillator Frequency of 7375 MHz is used for an inverted spectrum. A typical system will require a 2-watt BUC or higher, depending on the application. Although BUCs are available with very powerful amplifiers, it is unlikely that a VSAT installation will require more than 10W, even in less than ideal circumstances. SkyVision will provide you with the specific power requirements for your service.
You can also view the placement of the BUC (Block Up-Converter) below in the VSAT Installation Manual Components Chapter: