| 摘要 |
PURPOSE:To obtain a stable characteristic by modulating so as to stabilize a sound sub carrier wave and varying a loop gain to a different modulation system from each other. CONSTITUTION:The movable terminal of a switch 11 is changed over to fixed terminals 11c, 11d side, and the movable terminal of the switch 24 is changed over to the fixed terminal 24a side respectively by a switching signal supplied to a control terminal 28 at the time of FM modulation. An FM-modulated audio signal is outputted from an output terminal 27, and at this time, the loop gain of a PLL circuit 26 is set by a phase comparator 18 with a low value of e.g. about several Hz. On the other hand, the movable terminal of the switch 11 is changed over to the fixed terminal 24b side respectively by the switching signal supplied to the control terminal 28 at the time of AM modulation. Then, an AM-modulated audio signal is outputted from the output terminal 27. At this time, the loop gain of the circuit 26 becomes the high value of several tens to several hundreds of kHz. Thus, the modulation stabilizing the sound sub carrier wave is performed. |
