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一般的调频接收机中,其鉴频器的输出有这样一个特点,就是当天线输入端没有接收到讯号时,鉴频器输出噪声电平较大,且噪声频谱较宽(○——几十千赫)。当天线输入端存在有用讯号时,则鉴频器输出噪声被讯号抑制,仅存在语言讯号。利用这一特点,将鉴频器输出分成二路,一路是语言讯号,经去加重电路加至第一级低放管;另一路是30千赫左右的噪声,经噪声选频放大电路,经检波后的直流去控制第一级低放管的偏置,使得接收到信号时,第一级低放管的偏
In the general FM receiver, the output of the frequency discriminator has such a feature that when the antenna input does not receive the signal, the output noise level of the frequency discriminator is large and the noise spectrum is wide (○ - tens kilohertz). When there is a useful signal at the antenna input, the discriminator output noise is suppressed by the signal and only the speech signal is present. The use of this feature, the discriminator output is divided into two, all the way to the language signal, the deepening of the circuit added to the first level of low-drop tube; the other is about 30 kHz noise, amplified by the noise frequency selection circuit, the After the detection of DC to control the first level of low-tube bias, making the signal received, the first level of low-tube bias