| 摘要 |
PURPOSE:To always secure an establishment of the synchronism to the reference frequency of a satellite and thus increase the efficiency of transmission, by controlling the phase difference between the reference frequency from the satellite and the returned frequency from the self-station by the use of plural PLLs in the TDMA system. CONSTITUTION:At the ground station, the reference frequency fDR sent from a satellite and the signal fDi produced from the signal transmitted from the self- station and returned by the satellite are extracted by the receiver 2 plus the demodulators 3 and 3a. And the phase difference between the both signals is detected by the wave detector 8, and then the output fUi of the VCO 10 is controlled via the loop filter 9 so that the phase difference mentioned above may become zero. At the same time, the frequency conversion 7 is given to the signal fDR through the PLL consisting of the phase detector 8a. the loop filter 9a and the VCO 10a each. Then the phase difference is obtained between the output of conversion and the output fUi of the VCO 10 to control the output of the VCO 10a. As a result, the phenomenon in which the reference frequency of the satellite has a fluctuation at the ground station according to the Doppler effect can be absorbed perfectly at the ground station. Thus the synchronism can always be obtained with the reference frequency of the satellite at the ground station. |
