TABLE OF CONTENTS A simplified block diagram of the typical RF portion of the Earth station is shown in Figure 9.8. In it, we see many of the components of the standard bent-pipe type of repeater: a receive chain consisting of the antenna, LNB, and downconverter, and a transmit chain consisting of an upconverter, an HPA, and, again, the antenna. It is almost always the case that a transmit Earth station uses the same antenna to receive, since we are establishing communication with a common satellite. The LNB and HPA are connected to the same feed horn using a piece of waveguide plumbing called an ortho-mode transducer (OMT). The OMT then derives linear horizontal and vertical polarization for the antenna. The upconverters and downconverters interface with the rest of the station equipment at the IF, which typically is 70 MHz. An alternative is to package a block upconverter (70 MHz to L-band) with the HPA to allow the use of low cost coaxial transmission line for uplink as well as downlink. The upconverters and downconverters provide the translation from IF (typically 70 MHz) to the necessary RF frequencies assigned for the uplink and the downlink, respectively. An exception to using the standard IF is likely for compact UTs such as applied in MSS because of the potential for economies in the details of the internal design. For example, it might be possible for the modem to transmit directly on the uplink L-band frequency. The RF terminal often is contained...
