The involved coils or the inductors are very simply to wind. The circuit is self explanatory, just the inclusion of a general purpose BC559 transistor along with a few inexpensive passive components can be witnessed in the design. To make the above circuit self-contained, an additional transistor stage may be introduced for enabling the radio to play the music loudly over a small loudspeaker. Single Transistor Radio with Audio Amplifier This enforcement results in making the sawtooth effect on the received signal practically to zero, thus presenting an FM audio with much reduced background noise. This results in a fall in the collector voltage as the collector current rises, which in turn forces the emitter voltage to rise, prompting the emitter capacitor to negate the situation at the output. Here we pull out the emitter capacitor C5 ground link and connect it with the output. The output received from the above circuit would have greater content of sawtooth noise compared to the actual FM reception.Ī smart technique can be seen employed in the following single transistor FM radio circuit to attribute better efficiency to this simple design. ![]() The above design has one drawback, though. The procedure also gives rise to noise but only as long as a station is not being detected. The above happening forces the circuit to flip flop between two situations, oscillator OFF and oscillator ON, resulting a sawtooth frequency of about 50kHz at the output.Įach time the circuit flips across the above ON/OFF states, results in a significant stepping up of the amplitude which in turn constitutes greater amplification of the received signals. ![]() However this prompts the emitter capacitor to discharge, allowing the collector current to yet again resume its flow, initiating a fresh cycle of oscillation. ![]() This called for an increase in the feedback capacitor and also to use a transistor specifically designed for handling extreme high frequency ranges such as a BF494.įurther modifications include an inductor with the emitter of the transistor, and a capacitor across the emitter resistor of the transistor.ĭue to this the transistor is switched ON as soon as the base emitter voltage of the transistor falls significantly, resulting in an abrupt cut off in the oscillations. Here we have tried to enhance the design such that the amplitude becomes considerably magnified in order to turn OFF the transistor completely during the oscillations. How the One Transistor FM Radio Receiver WorksĪs mentioned above, the circuit is basically a single transistor superregenerative RF oscillator with a constant amplitude. However fewer components also means a few compromises involved, here the receiver requires a large metal base for grounding the unwanted signals, and for keeping the noise factor to the lowest, and also this system would work only in places where the reception is rather strong and thus may not be suitable in areas where the signal strength is thinner. It's basically based on a superregenerative audion receiver circuit where the use of minimal components becomes the main feature of the unit.
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