VHF radio receiver

Radio 1975, 1

The figure below shows a schematic diagram of a simple FM receiver. This receiver made with four transistors. The signal from the antenna through the trimmer capacitor C1 goes to the input of the first stage. This stage is a super-regenerative detector based on the transistor T1 circuit. The potentiometer R1 is used to adjust the regeneration. The trimmer C1 is used to adjust the coupling of the antenna to the resonant tank L1C2.

VHF radio receiver circuit diagram

T1 - BF310, T2..T4 - BC109;
C1, C2 - 15 pF, C3, C4, C4, C6, C7, C9, C11 - 10 nF, C5 - 0.5 uF, C8, C10, C12 - 180 pF

An audio signal from the output of the super-regenerative detector through a low-pass filter is fed to an audio amplifier. The filter reduces the noise level at the input of the audio amplifier.

The audio amplifier is based on transistors T2-T4. Each stage of the amplifier has a negative AC feedback loop (capacitors C8, C10 and C12). A load of the amplifier is the high-impedance headphones.

The power supply voltage is 1.5V. The consumption current is about 1.5 mA.

The coil L1 is wound on a mandrel of diameter 12 mm and length of 10 mm. It contains 3 turns of silver-plated wire with a diameter of 1.5 mm (AWG 15). The coil L1 is tapped in the middle. With this coil the frequency range is 100...170 MHz.

"Radio, televiziya, elektronika" 1974, N5.