| 摘要 |
PROBLEM TO BE SOLVED: To avoid momentary interruption at changeover of an active oscillator into a standby oscillator for a radio transmitter. SOLUTION: Output signals from two active/standby oscillators 11, 12 are synthesized by a 2-synthesizer 17 via a changeover switch and the synthesizer 17 provides an output. In the case of changeover of the active oscillator 11 into the standby oscillator 12, a phase detector 13 compares phases of output signals of the two oscillators 11, 12 to provide the detection result to a control circuit 14. The control circuit 14 closes a changeover switch of the standby oscillator when the phase difference is zero and opens the changeover switch of the active oscillator 11 just after. Furthermore, a phase adjustment device provided to an output of the standby oscillator 12 is controlled to match an input phase of the 2-synthesizer 17 with the phase of the active oscillator 11 and activates the changeover switch. Furthermore, a variable attenuator provided to the output of the active oscillator 11 is controlled up to a level till the effect of a beat frequency of the oscillators 11, 12 is avoided so as to conduct uninterruptible changeover. |
