Abstract: A mobile satellite communication terminal capable of performing satellite communication both indoors and outdoors. In an indoor mode, the mobile satellite communication terminal includes an indoor terminal for carrying out transmission or reception of a signal through a ground radio link and a repeater terminal installed in such a location that the repeater terminal can get an unobstructed view of a satellite for carrying out transmission or reception of a signal through a satellite communication link. In an outdoor mode, an antenna of the indoor unit is replaced by an antenna for the satellite communication link, whereby the indoor terminal can be used as an outdoor terminal.

Abstract: In order that communication may be performed independently of indoors or outdoors, in this mobile satellite communication terminal, when it is used indoors, the indoor terminal transmitting and receiving a signal in the ground radio channel is connected to the repeater terminal installed at a position from which the satellite can be seen by the ground radio channel, further, the repeater terminal communicates with the satellite by using the satellite channel. On the other hand, when it is used outdoors, the outdoor terminal is constituted by mounting the outdoor unit for the satellite channel consisting of the antenna for the satellite channel and the radio frequency section instead of the indoor unit consisting of the antenna for the ground radio channel and the radio frequency section of the indoor terminal.

Abstract: A power supply protection circuit is provided for use in a mobile satellite communication apparatus which is connected to an external power supply for driving a load circuit therein. The power supply protection circuit includes first and second relay switches which electrically connect a power supply line and common ground line, respectively, to the load circuit when the power supply is normally connected in polarity and which interrupt the power supply and common ground lines leading to the load circuit when the power supply is erroneously connected in polarity. The first and the second relay switches are controlled by a diode to be closed when the power supply is normally connected to the load circuit and to be opened when the power supply is erroneously connected to the load circuit. A resistor supplies a current level adapted to operate the first and the second relay switches and the diode.

Abstract: An intermittently transmitted burst modulation signal is demodulated to a baseband signal and multiplied with a variable gain coefficient. A range where a difference signal of a power signal of the multiplied signal from a reference power level is included, in a plurality of level ranges, is decided. A loop constant is determined in accordance with the decided range and is multiplied with the difference signal. An integrated multiplied difference signal with the loop constant is used for changing the variable gain constant.