| 摘要 |
PURPOSE:To make a demodulation characteristic stable without being affected with the C/N and the temperature characteristic of a digital modulation signal by applying direct frequency division to a recovered carrier, counting the frequency and adjusting minutely a voltage controlled oscillator at synchronization. CONSTITUTION:When a synchronizing detection signal 5 from a carrier recovery circuit 4 is at a level of asynchronization state, a comparison control means 2 sends a control signal to a frequency control means 111 to implement frequency sweep of a VCO 112. When the synchronizing detection signal 5 reaches a level of the synchronization state, the frequency sweep is stopped and the frequency of the recovered carrier frequency-divided by a frequency divider means 108 is counted by a frequency count means 109. Then the obtained count is compared with a relevant reference value at a comparison control means 2 via a data line 114 and the oscillating frequency of the VCO112 is fine-adjusted so that an error is set within an allowable range. Thus, the effect of the C/N of the signal inputted to a demodulation means is not caused and the frequency of the digital modulation signal is made stable without being affected by a temperature characteristic of the circuit constitution. |
