| 摘要 |
PURPOSE:To keep a frequency shift of an output signal to a constant value by feeding back an output level of an FM modulation means using a part of an output of a VCO to a voltage control ATT controlling a data signal level. CONSTITUTION:A part of an output of the VCO 23 is extracted by branching devices 24, 28 and inputted to a mixer 36. The mixer 36 mixes an output of a frequency synthesizer comprising a VCO 40 of PLL constitution and an output of the VCO 23, and the output is detected by an FM detector 38 through a BPF 37, the detected output is rectified by a rectifier 48 and the result is input ted to the voltage control ATT 21 as a control voltage signal 39. The oscillating frequency of a VCO 40 is set by using a frequency dividing ratio data 47 offset ting a frequench division ratio data 31 deciding the oscillating frequency of the VCO 23 by a certain value. Since a signal branched from the VCO 23 is subjected to FSK modulation by using an input signal 18, the output of the detector 38 is a detected output in response to the frequency shift of an FSK, the attenuation of the ATT 21 is controlled depending on the output of the signal 39 to make the frequency shift of the output signal 27 constant. |
