Abstract: A satellite broadcast communications system, in which a host station sends packet-multiplexed signals to a plurality of terminal stations via a communications satellite, specifically improving efficiency in data retransmission operations without sacrificing the channel capacity of the satellite communications link. Broadcast schedule transmission means transmits the broadcast schedule, which contains the title and transmission time of each transmission data, to every terminal station via the communications satellite. Based on the broadcast schedule, composite information transmission means broadcasts various data to the terminal stations. Broadcast schedule reception means receives the broadcast schedule, and based on the received broadcast schedule, desired information reception means selectively receives desired information at the scheduled transmission time.

Abstract: A multi-carrier radio transmission apparatus provided with an idling detection means for detecting when all of a plurality of modulators are idling and a selective automatic level control means for selectively driving only specific modulators among a plurality of modulators so as to cause them send out their modulated outputs when receiving an idling detection signal from the idling detection means and for enabling an automatic level control unit to perform an automatic level control operation only when receiving an idling detection signal, whereby it is possible to realize a power detector which can exhibit an effect equivalent to that of a diode with a wide dynamic range even when use is made of a diode with a narrow dynamic range.

Abstract: The present invention discloses a phase lock loop circuit which recovers a carrier for demodulating a PSK signal wherein a sweep signal is suspended when a decision signal indicates the phase-locked state. The level of the sweep signal is held and applied to the phase lock loop at the time the circuit becomes phase-locked, thereby an unwanted sweep signal component is no longer generated when the sweep stops. Thus stable phase-locked operation can be realized.

Abstract: In the base-band carrier-recovery circuit used in the demodulator of radio equipment using a PSK modulated signal, a first doubled signal (sin 2.theta.) is obtained by using first and second outputs (sin .theta., cos .theta.) in-phase quadrature with each other from an in-phase quadrature detecting means. A second doubled signal (cos 2.theta.) having a phase difference of 90 degrees from the first doubled signal (sin 2.theta.) is obtained by fullwave rectifying the second output (cos .theta.) and transforming the output waveform. Thereafter a quadrupled signal (sin 4.theta.) is generated from the first and second doubled signals. The quadrupled signal is then fed back to a VCO via a loop filter, thereby recovering the reference carrier signal which is in phase with the received PSK modulated signal.