| 摘要 |
PURPOSE:To reduce requirements of a modulator demodulator greatly by using a single high-stability original oscillator which is synchronized with a high-stability external clock frequency as a common original oscillator for an earth station and a satellite, and generating plural desired radio frequency signals, an intermediate frequency signal, and a clock signal. CONSTITUTION:The earth station 26 is provided with the original oscillator 27 which is synchronized with the external clock frequency. For example, a high- stability digital clock supply device 20 provided in a ground network 28 supplies the clock signal to the original oscillator 27, which is then synchronized with the clock signal. The original oscillator 27 is a phase locked loop and a phase comparator 32 makes a phase comparison between the output of a VCO31 and the clock signal of the clock supply device 29 and supplies its comparison output to the VCO31 as a control signal. This highly stabilized clock 33 is branched into many signals and one of them is converter into a high-stability frequency signal close to a radio frequency by the phase-locked loop 38 which consists of a phase comparator 34, low-pass filter 35, voltage-controlled oscillator 36, and frequency divider 37.
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