The simplest FM receiver

The simplest FM receiver

This is likely one of the simplest and smallest FM receivers for receiving local FM radio stations. Its simple design makes it ideal as a pocket-sized FM receiver. The receiver's audio output is amplified by an LM386 amplifier chip, which can drive a small speaker or headphones. The circuit is powered by three AAA or AA batteries. The FM receiver section uses two RF transistors to convert the frequency-modulated signal into audio. An L1 coil and a 22pF variable capacitor form a tuning resonant circuit for tuning to any available FM radio station.

The L1 coil is a crucial component of the receiver. It is made of 18 SWG enameled copper wire. It is wound four times around a ballpoint pen to achieve an inner diameter of 0.5 cm. The inductance, measured with an LC meter, is 0.54 µH. Before soldering to the PCB, ensure the enamel coating is removed from the wire ends. You may need to adjust the coil winding spacing for clear audio reception.

The receiver performs well using BF494 or BF199 NPN RF transistors, which have a gain bandwidth exceeding 1100 MHz. Good alternatives include the 2N5109 with a gain bandwidth of 1200 MHz; the 2SS9014 with a gain bandwidth of 270 MHz; and the 2SS9018 with a gain bandwidth of 800 MHz.

For the antenna, use a short piece of wire (60 cm / 2 ft) to couple it to a 10 pF capacitor. R2 10K potentiometer controls the receiver's volume.