三、中频放大电路变频后得到的中频信号是很微弱的,为了获得足够的增益,一般超外差收音机设置了两级中频放大电路,并在第一级中放输入端加有自动增益控制(AGC)。图3为典型的中放实用电路,Q_2和Q_3为中放管,B_4和B_5既是中频选频回路,又是级间偶合器件。 Third, the intermediate frequency amplifier circuit After the IF signal is very weak, in order to obtain sufficient gain, the general superheterodyne radio set up two intermediate frequency amplifier circuit, and placed in the first stage input plus automatic gain control AGC). Figure 3 shows a typical mid-amplifier practical circuit, Q_2 and Q_3 for the release tube, B_4 and B_5 both IF frequency selection loop, but also interstage coupling device.