| 摘要 |
A reliable earth terminal for satellite communications systems capable of unattended operation for extended periods of time is disclosed. The terminal includes an antenna with a single fixed reflector which can provide multiple beams, each of which can be positioned by small feed motion. The transmitter is of a modular construction, using a relatively low power traveling wave tube power amplifier for each increment in the operating band. The transmitting chains are designed to carry voice, data, or television signals to a satellite and include a modulator, IF amplifier, band-limiting filter, frequency converter, and power amplifier. Each amplifier is capable of operating over the full operating band; however, operation of each amplifier is limited to an assigned increment through the use of band-limiting filters. A single, redundant high power amplifier is provided and may be remotely switched into any one of the transmitting chains in the event of a failure. Amplifier outputs are connected to the antenna through a directional filter multiplexer. The receiver includes a low noise preamplifier featuring modular, "fail-soft" design. The receiving chains following the low noise preamplifier are channelized into band increments corresponding to those of the transmitting chains with separate converter and demodulator modules for each carrier. All subsystems are broadband, and channel bandwidth is determined only by intermediate frequency band pass filters. Prime power is low voltage battery banks constantly recharged by a commercial power source. The terminal can be operated for a limited period of time solely on the battery bands during commercial outages. A back-up motor generator provides recharging power during extended periods of commercial outages. The terminal is monitored and controlled from a central control point. Since the terminal is both automatic and self-protecting, remote control is limited to parameter adjustments required for normal operation, such as antenna feed positioning, changes in transmitter power, and switching to the spare power amplifier or turning off any carrier. |
