VHF radio receiver


Posted on Feb 5, 2014

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


VHF radio receiver
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trimmer C1 is used to adjust the coupling of the antenna to the resonant tank L1C2. 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 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. 170MHz.




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