Debug-free FM antenna amplifier

The amplifier principle is as follows:

The input end is connected to the antenna with a 75-ohm high-frequency coaxial cable. The signal is first filtered by an FM bandpass filter to remove other stray signals other than FM to improve the signal-to-noise ratio and reduce intermodulation interference. This filter must not be omitted when making it yourself. Then the signal is input into the amplifier circuit composed of BG1 and BG2. This design only uses one stage of amplification to prevent the gain signal from being too high, which will make the intermodulation more severe, the strong station will affect the weak station, and the selectivity will deteriorate. Another problem is that it is easy to self-excite, which increases the difficulty of debugging. At the same time, this stage of amplification uses a common emitter and common base circuit, so the gain is high, the frequency band is wide, the operation is stable, and it is easy to make under amateur conditions. In addition, the author has carefully designed this amplifier circuit into a debugging-free mode, which greatly improves the success rate of production. Finally, the signal is output to the room by a coaxial cable. Since the amplifier circuit is installed on the outdoor antenna and the power supply is placed indoors, a frequency isolation circuit composed of L1, L2, C3, and C4 is set in the circuit design to enable the high-frequency cable to send the DC power supply to the amplifier while transmitting the signal, and the gain of the amplifier can be changed by adjusting the value of the potentiometer R (L). The author uses the shell of the splitter as a shield, and the effect is quite good. The specific circuit diagram is as follows: